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Diagnosis, Treatment, and Prevention of Malaria in the US : A Review

• 1 Department of Medicine (Infectious Diseases), Albert Einstein College of Medicine, Bronx, New York
• 2 D. Samuel Gottesman Library, Albert Einstein College of Medicine, Bronx, New York
• Medical News & Perspectives Vaccine Development Is Charting a New Path in Malaria Control Bridget M. Kuehn, MSJ JAMA
• JAMA Patient Page Patient Information: Malaria Kristin Walter, MD, MS; Chandy C. John, MD, MS JAMA
• Global Health Updated Malaria Recommendations for Children and Pregnant People Howard D. Larkin JAMA
• Medical News in Brief First Ever Malaria Vaccine to Be Distributed in Africa Emily Harris JAMA

Importance   Malaria is caused by protozoa parasites of the genus Plasmodium and is diagnosed in approximately 2000 people in the US each year who have returned from visiting regions with endemic malaria. The mortality rate from malaria is approximately 0.3% in the US and 0.26% worldwide.

Observations   In the US, most malaria is diagnosed in people who traveled to an endemic region. More than 80% of people diagnosed with malaria in the US acquired the infection in Africa. Of the approximately 2000 people diagnosed with malaria in the US in 2017, an estimated 82.4% were adults and about 78.6% were Black or African American. Among US residents diagnosed with malaria, 71.7% had not taken malaria chemoprophylaxis during travel. In 2017 in the US, P falciparum was the species diagnosed in approximately 79% of patients, whereas P vivax was diagnosed in an estimated 11.2% of patients. In 2017 in the US, severe malaria, defined as vital organ involvement including shock, pulmonary edema, significant bleeding, seizures, impaired consciousness, and laboratory abnormalities such as kidney impairment, acidosis, anemia, or high parasitemia, occurred in approximately 14% of patients, and an estimated 0.3% of those receiving a diagnosis of malaria in the US died. P falciparum has developed resistance to chloroquine in most regions of the world, including Africa. First-line therapy for P falciparum malaria in the US is combination therapy that includes artemisinin. If P falciparum was acquired in a known chloroquine-sensitive region such as Haiti, chloroquine remains an alternative option. When artemisinin-based combination therapies are not available, atovaquone-proguanil or quinine plus clindamycin is used for chloroquine-resistant malaria. P vivax, P ovale, P malariae, and P knowlesi are typically chloroquine sensitive, and treatment with either artemisinin-based combination therapy or chloroquine for regions with chloroquine-susceptible infections for uncomplicated malaria is recommended. For severe malaria, intravenous artesunate is first-line therapy. Treatment of mild malaria due to a chloroquine-resistant parasite consists of a combination therapy that includes artemisinin or chloroquine for chloroquine-sensitive malaria. P vivax and P ovale require additional therapy with an 8-aminoquinoline to eradicate the liver stage. Several options exist for chemoprophylaxis and selection should be based on patient characteristics and preferences.

Conclusions and Relevance   Approximately 2000 cases of malaria are diagnosed each year in the US, most commonly in travelers returning from visiting endemic areas. Prevention and treatment of malaria depend on the species and the drug sensitivity of parasites from the region of acquisition. Intravenous artesunate is first-line therapy for severe malaria.

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Daily JP , Minuti A , Khan N. Diagnosis, Treatment, and Prevention of Malaria in the US : A Review . JAMA. 2022;328(5):460–471. doi:10.1001/jama.2022.12366

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• Published: 03 August 2017
• Margaret A. Phillips 1 ,
• Jeremy N. Burrows 2 ,
• Christine Manyando 3 ,
• Rob Hooft van Huijsduijnen 2 ,
• Wesley C. Van Voorhis 4 &
• Timothy N. C. Wells 2  

Nature Reviews Disease Primers volume  3 , Article number:  17050 ( 2017 ) Cite this article

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Malaria is caused in humans by five species of single-celled eukaryotic Plasmodium parasites (mainly Plasmodium falciparum and Plasmodium vivax ) that are transmitted by the bite of Anopheles spp. mosquitoes. Malaria remains one of the most serious infectious diseases; it threatens nearly half of the world's population and led to hundreds of thousands of deaths in 2015, predominantly among children in Africa. Malaria is managed through a combination of vector control approaches (such as insecticide spraying and the use of insecticide-treated bed nets) and drugs for both treatment and prevention. The widespread use of artemisinin-based combination therapies has contributed to substantial declines in the number of malaria-related deaths; however, the emergence of drug resistance threatens to reverse this progress. Advances in our understanding of the underlying molecular basis of pathogenesis have fuelled the development of new diagnostics, drugs and insecticides. Several new combination therapies are in clinical development that have efficacy against drug-resistant parasites and the potential to be used in single-dose regimens to improve compliance. This ambitious programme to eliminate malaria also includes new approaches that could yield malaria vaccines or novel vector control strategies. However, despite these achievements, a well-coordinated global effort on multiple fronts is needed if malaria elimination is to be achieved.

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Introduction.

Malaria has had a profound effect on human lives for thousands of years and remains one of the most serious, life-threatening infectious diseases 1 – 3 . The disease is caused by protozoan pathogens of the Plasmodium spp.; Plasmodium falciparum and Plasmodium vivax , for which humans are the exclusive mammalian hosts, are the most common species and are responsible for the largest public health burden. Malaria is transmitted by the bite of Plasmodium spp.-infected female mosquitoes of the Anopheles genus 1 – 3 . During a blood meal, infected mosquitoes inject — along with their anticoagulating saliva — sporozoites, which are the infective, motile stage of Plasmodium spp. Sporozoites journey through the skin to the lymphatics and into hepatocytes in the liver ( Fig. 1 ). Inside the hepatocyte, a single sporozoite can generate tens of thousands of merozoites (the stage that results from multiple asexual fissions (schizogony) of a sporozoite within the body of the host), which are released into the bloodstream where they enter red blood cells to replicate (erythrocytic schizogony). A fraction of merozoites (those that are sexually committed) also differentiate and mature into male and female gametocytes, which is the stage that infects the mosquito host when it takes a blood meal 4 , 5 . The onset of clinical symptoms generally occurs 7–10 days after the initial mosquito bite. P. vivax and Plasmodium ovale also have dormant forms, called hypnozoites, which can emerge from the liver years after the initial infection 6 , leading to relapse if not treated properly.

The mosquito vector transmits the Plasmodium spp. parasite in the sporozoite stage to the host during a blood meal. Within 30–60 minutes, sporozoites invade liver cells, where they replicate and divide as merozoites. The infected liver cell ruptures, releasing the merozoites into the bloodstream, where they invade red blood cells and begin the asexual reproductive stage, which is the symptomatic stage of the disease. Symptoms develop 4–8 days after the initial red blood cell invasion. The replication cycle of the merozoites within the red blood cells lasts 36–72 hours (from red blood cell invasion to haemolysis). Thus, in synchronous infections (infections that originate from a single infectious bite), fever occurs every 36–72 hours, when the infected red blood cells lyse and release endotoxins en masse 70 – 72 . Plasmodium vivax and Plasmodium ovale can also enter a dormant state in the liver, the hypnozoite. Merozoites released from red blood cells can invade other red blood cells and continue to replicate, or in some cases, they differentiate into male or female gametocytes 4 , 5 . The transcription factor AP2-G (not shown) has been shown to regulate the commitment to gametocytogenesis. Gametocytes concentrate in skin capillaries and are then taken up by the mosquito vector in another blood meal. In the gut of the mosquito, each male gametocyte produces eight microgametes after three rounds of mitosis; the female gametocyte matures into a macrogamete. Male microgametes are motile forms with flagellae and seek the female macrogamete. The male and female gametocytes fuse, forming a diploid zygote, which elongates into an ookinete; this motile form exits from the lumen of the gut across the epithelium 254 as an oocyst. Oocysts undergo cycles of replication and form sporozoites, which move from the abdomen of the mosquito to the salivary glands. Thus, 7–10 days after the mosquito feeds on blood containing gametocytes, it may be ‘armed’ and able to infect another human with Plasmodium spp. with her bite. Drugs that prevent Plasmodium spp. invasion or proliferation in the liver have prophylactic activity, drugs that block the red blood cell stage are required for the treatment of the symptomatic phase of the disease, and compounds that inhibit the formation of gametocytes or their development in the mosquito (including drugs that kill mosquitoes feeding on blood) are transmission-blocking agents. *Merozoite invasion of red blood cells can be delayed by months or years in case of hypnozoites. ‡ The number of days until symptoms are evident. § The duration of gametogenesis differs by species. || The maturation of sporozoites in the gut of the mosquito is highly temperature-dependent. Adapted with permission from Ref. 255 , Macmillan Publishers Ltd.

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The consequences of Plasmodium spp. infection vary in severity depending on the species and on host factors, including the level of host immunity, which is linked to the past extent of parasite exposure 7 , 8 . Malaria is usually classified as asymptomatic, uncomplicated or severe (complicated) 9 ( Box 1 ). Typical initial symptoms are low-grade fever, shaking chills, muscle aches and, in children, digestive symptoms. These symptoms can present suddenly (paroxysms), and then progress to drenching sweats, high fever and exhaustion. Malaria paroxysmal symptoms manifest after the haemolysis of Plasmodium spp.-invaded red blood cells. Severe malaria is often fatal, and presents with severe anaemia and various manifestations of multi-organ damage, which can include cerebral malaria 8 ( Box 1 ). Severe malaria complications are due to microvascular obstruction caused by the presence of red blood cell-stage parasites in capillaries 8 , 10 , 11 . This Primer focuses on our understanding of malaria pathology in the context of parasite and vector biology, progress in diagnostics and new treatments (drugs and vaccines), chemoprotection and chemoprevention.

Box 1: Malaria key terms

Asymptomatic malaria: can be caused by all Plasmodium spp.; the patient has circulating parasites but no symptoms.

Uncomplicated malaria: can be caused by all Plasmodium spp. Symptoms are nonspecific and can include fever, moderate-to-severe shaking chills, profuse sweating, headache, nausea, vomiting, diarrhoea and anaemia, with no clinical or laboratory findings of severe organ dysfunction.

Severe (complicated) malaria: usually caused by infection with Plasmodium falciparum , although less frequently it can also be caused by Plasmodium vivax or Plasmodium knowlesi . Complications include severe anaemia and end-organ damage, including coma (cerebral malaria), pulmonary complications (for example, oedema and hyperpnoeic syndrome 228 ), and hypoglycaemia or acute kidney injury. Severe malaria is often associated with hyperparasitaemia and is associated with increased mortality.

Placental malaria: parasites are present in the placenta, leading to poor outcomes for the fetus and possibly for the mother.

Epidemiology

Human malaria parasites are transmitted exclusively by ∼ 40 species of the mosquito genus Anopheles 12 . During Anopheles spp. mating, males transfer high levels of the steroid hormone 20-hydroxyecdysone to the females, and the presence of this hormone has been associated with favourable conditions for Plasmodium spp. development 13 . Malaria-competent Anopheles spp. are abundant and distributed all over the globe, including the Arctic. However, the efficacy of malaria transmission depends on the vector species and, therefore, varies considerably worldwide; for example, in tropical Africa, Anopheles gambiae is a major and highly efficient vector 14 . The first WHO Global Malaria Eradication Programme (1955–1972) involved, in addition to chloroquine-based treatments, large-scale insecticide campaigns using dichlorodiphenyltrichloroethane (DDT) 15 . This strategy was quite effective against P. falciparum ; although the mosquitoes gradually repopulated DDT-treated areas (because they developed resistance to the insecticide, and the use of DDT itself waned owing to its costs and increasing environmental concerns), these areas have often remained malaria-free and in some cases still are. More-selective vector control approaches, such as the use of insecticide-treated bed nets and indoor residual spraying, have eliminated malaria from several areas (see Diagnosis, screening and prevention, below). However, mosquito resistance to insecticides is a growing concern. Of the 78 countries that monitor mosquito resistance to insecticides, 60 have reported resistance to one or more insecticides since 2010 (Ref. 16 ).

The parasite

Plasmodium spp. are single-celled eukaryotic organisms 17 – 19 that belong to the phylum Apicomplexa, which is named for the apical complex that is involved in host cell invasion. A discussion of the parasite genome and the genetic approaches used to study parasite biology is provided in Box 2 . Of the five human-infective Plasmodium spp., P. falciparum causes the bulk of malaria-associated morbidity and mortality in sub-Saharan Africa, with mortality peaking in the late 1990s at over 1 million deaths annually in the continent 20 ( Fig. 2 ). P. falciparum is associated with severe malaria and complications in pregnancy ( Box 3 ); most malaria-related deaths are associated with this species, which kills ∼ 1,200 African children <5 years of age each day 21 . However, P. falciparum is also found in malarious tropical areas around the world. P. vivax is found in malarious tropical and temperate areas, primarily Southeast Asia, Ethopia and South America, and generally accounts for the majority of malaria cases in Central and South America and in temperate climates. This distribution can be explained by the fact that P. vivax can survive in climatically unfavourable regions and can stay dormant in a hypnozoite form in its human host's liver for many years. Furthermore, many Africans are negative for the Duffy antigen (also known as atypical chemokine receptor 1) on the surface of red blood cells, and this genotype provides protection from P. vivax malaria, as it makes it more difficult for P. vivax to bind to and penetrate red blood cells 22 . However, some cases of P. vivax transmission to Duffy antigen-negative individuals have been reported, which suggests that alternative mechanisms of invasion might be present in some strains, and this might portend the escalation of P. vivax malaria to Africa 23 , 24 . P. ovale is also found in Africa and Asia, but is especially prevalent in West Africa. Two sympatric species exist: P.o. curtisi and P.o. wallikeri 25 . Plasmodium malariae — which can be found worldwide but is especially prevalent in West Africa — causes the mildest infections, although it has been associated with splenomegaly or renal damage upon chronic infection. Plasmodium knowlesi — which was initially considered as a parasite of non-human primates — can not only cause malaria in humans but can also lead to severe and even fatal malaria complications 26 , 27 . The reasons for the emergence of P. knowlesi in humans are not yet fully understood but are possibly linked to land-use changes that have brought humans into close contact with P. knowlesi -infected mosquitoes 28 . Regardless, the possible recent emergence of a form of malaria as a zoonosis poses obvious complications for elimination. In addition, co-infections between P. falciparum and P. vivax have been well-documented and have been reported to occur in up to 10–30% of patients living in areas where both parasites are prevalent 29 , 30 . Mixed infections can also include other species such as P. ovale and P. malariae , and newer diagnostic methods are being developed that will enable better assessment of the frequency and distribution of these types of co-infection (for example, Ref. 31 ).

The most-deadly malaria parasite, Plasmodium falciparum , is only found in tropical areas because its gametocytes require 10–18 days at a temperature of >21°C to mate and mature into infectious sporozoites inside the vector 256 . This development timeline is only possible in hot, tropical conditions; where the ambient temperature is lower, mosquitoes can still propagate, but sporozoite maturation is slowed down and, therefore, incomplete, and parasites perish without progeny when the mosquitoes die. Thus, P. falciparum is quite temperature-sensitive; a global temperature rise of 2–3 °C might result in an additional 5% of the world population (that is, several hundred million people) being exposed to malaria 257 . Of note, Plasmodium vivax and Plasmodium ovale can develop in mosquitoes at ambient temperatures as low as 16 °C. The abilities of these parasites to propagate at subtropical temperatures and to remain in the hypnozoite state in the liver are likely to explain their ability to survive dry or cold seasons, and the broader global distribution of these parasites 258 . Countries coded ‘not applicable’ in the Figure were not separately surveyed. Figure based on data from Ref. 16 , WHO.

Box 2: The Plasmodium spp. genome and genomic tools for understanding gene function

Characteristics of the Plasmodium spp. genome

Each haploid genome comprises 23 Mb, which encode the programme for the complex life cycle of the parasite within ∼ 5,500 genes 17 – 19 .

Many genes encode proteins that have similarities to host proteins, many are novel, and many (approximately half) remain annotated as genes with hypothetical or of unknown function.

The Plasmodium spp. genome includes an essential plastid, the apicoplast, which is derived from two sequential endosymbiotic events, and encodes genes from both plant (red algal) and bacterial (cyanobacterium) origin 229 . The bacterial origin of some enzymes encoded by the plastid makes Plasmodium spp. sensitive to some antibacterial agents, whereas the plant-like pathways can be targeted by some herbicides. This plastid is one source of genes that differ from the host and that have been considered as potential drug targets.

Gene transcription across the Plasmodium spp. intra-red blood cell life cycle follows a preprogrammed cyclic cascade during which most genes are expressed at peak levels only once per life cycle 230 – 232 . Genes that encode cell surface proteins involved in host–parasite interactions are the exception.

Gene expression patterns have been reported to lack responses to perturbations. Minimal changes were observed after treatment with antifolates and chloroquine; however, larger changes have been observed for other drug classes 233 , 234 . Species-specific differences in transcription have been observed that seem to be linked to the mammalian host 235 .

Ribosome profiling has demonstrated that transcription and translation are tightly coupled for 90% of genes 236 . Exceptions of translationally upregulated genes are typically found for proteins involved in merozoite egress and invasion.

Epigenetic mechanisms to control gene expression include post-translational histone modifications (methylation and acetylation of the amino terminus are the best-characterized). Many of these modifications have been linked to parasite development 63 , 237 .

Genomic tools

Gene knockouts are possible, but RNA interference-mediated knockdown mechanisms do not function in Plasmodium spp. 238 , 239 .

Regulated RNA aptamer-based approaches have led to methods that enable gene knockouts to be functionally rescued; these methods are key for studying essential genes 238 , 239 .

CRISPR–Cas9-directed genome editing has greatly facilitated the genetic manipulation of Plasmodium falciparum 238 , 239 .

Barcoded mutant Plasmodium berghei libraries have been developed to screen for competitive fitness across tens of mutants in a single mouse 240 .

The in vitro selection of drug-resistant mutant parasites followed by whole-genome sequencing has also become a well-established method for revealing candidate drug targets 241 .

Metabolomics approaches facilitate the understanding of Plasmodium spp. biology, and have been used to profile several antimalarial compounds that have both known and unknown mechanisms of action 242 .

Box 3: Malaria and pregnancy

Pregnant women are more susceptible to Plasmodium spp. infection, particularly in their first pregnancy, as the mother-to-be has not yet acquired immunity to parasites that express the protein variant surface antigen 2-CSA (VAR2CSA) 35 . VAR2CSA on the surface of infected red blood cells facilitates adhesion to chondroitin sulfate A (which is part of placental proteoglycans), leading to red blood cell sequestration in the placenta 7 , 64 . The risk of placental malaria is reduced in multigravid women from endemic areas, who generally have antibodies against VAR2CSA 65 – 67 .

Malaria during pregnancy leads to increased risks to the mother and fetus 36 , 243 . Most studies have focused on sub-Saharan Africa; however, pregnancy-related risks are a problem throughout the world, including in Latin America, where Plasmodium vivax is the dominant causative agent 244 .

Placental malaria might be asymptomatic or clinically mild, but it also leads to an increased risk of death for both the fetus and the mother. It predisposes to miscarriage, stillbirth, preterm delivery and babies with low birth weight whose quality of life will probably be poor because of cognitive, mobility, self-care and sensation limitations; such babies also have a high mortality rate 36 , 243 .

Intermittent preventive treatment with sulfadoxine–pyrimethamine in endemic regions is recommended and is generally administered at each antenatal visit following quickening 108 , although the emergence of resistance is threatening its efficacy 245 .

Treatments for pregnant women must take into account the availability of safety data for the fetus. As a consequence, newer treatments require time to obtain sufficient confirmation of their tolerability in the different trimesters. The WHO recommends quinine sulfate and clindamycin in the first trimester. One study has shown that artemisinin derivatives provide comparable safety to quinine 246 , but, at the time of publication, the results of this study have not yet been incorporated into the WHO guidelines. In the second or third trimester, the WHO recommends artemisinin-based combination therapies 108 .

The treatment of pregnant women with P. vivax , Plasmodium ovale or Plasmodium malariae infection can also include chloroquine, unless resistance is suspected 108 . Women who are at a high risk of relapse can be given weekly chloroquine chemoprophylaxis until after delivery. Follow-up therapy with primaquine against P. vivax and P. ovale hypnozoites is not thought to be safe during pregnancy.

The disease

Malaria remains a major burden to people residing in resource-limited areas in Africa, Asia and Central and South America ( Fig. 2 ). An estimated 214 million cases of malaria occurred in 2015 (Ref. 16 ). Africa bears the brunt of the burden, with 88% of the cases, followed by Southeast Asia (10%), the eastern Mediterranean region (2%) and Central and South America (<1%). Malaria continues to kill over three-times as many people as all armed conflicts; in 2015, there were an estimated 438,000 (Ref. 16 ) — 631,000 (Ref. 20 ) deaths resulting from malaria, compared with an estimated 167,000 deaths due to armed conflicts 32 , 33 . In areas of continuous transmission of malaria, children <5 years of age and the fetuses of infected pregnant women experience the most morbidity and mortality from the disease. Children >6 months of age are particularly susceptible because they have lost their maternal antibodies but have not yet developed protective immunity. In fact, adults and children >5 years of age who live in regions of year-round P. falciparum transmission develop a partial protective immunity owing to repeated exposure to the parasite. There is evidence that immunity against P. vivax is acquired more quickly 34 . Individuals with low protective immunity against P. falciparum are particularly vulnerable to severe malaria. Severe malaria occurs in only 1% of infections in African children and is more common in patients who lack strong immune protection (for example, individuals who live in low-transmission settings, children <5 years of age and naive hosts). Severe malaria is deadly in 10% of children and 20% of adults 7 . Pregnant women are more susceptible to Plasmodium spp. infection because the placenta itself selects for the emergence of parasites that express receptors that recognize the placental vasculature; these receptors are antigens to which pregnant women have not yet become partially immune 7 ( Box 3 ). This vulnerability increases the risk of miscarriage; parasitaemia in the placenta can have adverse effects on the fetus 35 – 37 ( Box 3 ).

Co-infection of Plasmodium spp. with other pathogens — including HIV, Mycobacterium tuberculosis and helminths — is common. HIV-infected adults are at an increased risk of severe malaria and death 38 . The overall prevalence of helminth infection is very high (>50% of the population) in malaria-endemic regions and is associated with increased malaria parasitaemia 39 . Surprisingly, naturally occurring iron deficiency and anaemia protect against severe malaria, which was an unexpected finding 40 , as numerous clinical studies have aimed to fortify children and prevent anaemia by distributing iron supplements 41 .

From 2000 to 2015, the incidence of malaria fell by 37% and the malaria mortality rate fell by 60% globally 16 . The WHO attributes much of this reduction of malaria-associated morbidity and mortality to the scale-up of three interventions: insecticide-treated bed nets (69% of the reduction), artemisinin-based combination therapies (ACTs; 21%) and indoor residual insecticide spraying (10%) 16 (see Diagnosis, screening and prevention, below). Until ACT was introduced, progress in malaria control in most malarious countries was threatened or reversed by the nearly worldwide emergence of chloroquine-resistant and sulfadoxine–pyrimethamine-resistant P. falciparum strains and, more recently, of other resistant Plasmodium spp. ACT has become the antimalarial medicine of choice in most malarious areas, and demonstrates rapid parasite clearance, superior efficacy (compared with other clinically approved drugs) and >98% cure rates (typically defined as the percentage of patients who remain malaria-free for 28 days; re-infection events do not count as a recurrence). ACTs achieve these results even in strains that are resistant to older antimalarials, effectively turning the tide against antimalarial drug resistance. However, the emergence of artemisinin-resistant strains in Southeast Asia threatens the usefulness of ACTs 42 – 45 (see Drug resistance, below).

Mechanisms/pathophysiology

The red blood cell stage.

As previously mentioned, the red blood cell stage of Plasmodium spp. infection is the cause of symptomatic malaria, as red blood cells are the site of abundant parasite replication.

Invasion . Plasmodium spp. parasites gain entry into the red blood cell through specific ligand–receptor interactions mediated by proteins on the surface of the parasite that interact with receptors on the host erythrocyte (mature red blood cell) or reticulocyte (immature red blood cell) 46 ( Fig. 3 ). Whereas P. falciparum can invade and replicate in erythrocytes and reticulocytes, P. vivax and other species predominantly invade reticulocytes, which are less abundant than erythrocytes 47 . Most of the parasite erythrocyte-binding proteins or reticulocyte-binding proteins that have been associated with invasion are redundant or are expressed as a family of variant forms; however, for P. falciparum , two essential red blood cell receptors (basigin and complement decay-accelerating factor (also known as CD55)) have been identified ( Fig. 3 ).

Invasion occurs through a multistep process 259 . During pre-invasion, low-affinity contacts are formed with the red blood cell membrane. Reorientation of the merozoite is necessary to enable close contact between parasite ligands and host cell receptors, and this is then followed by tight junction formation. In Plasmodium falciparum , a forward genetic screen has shown that complement decay-accelerating factor (not shown) on the host red blood cell is essential for the invasion of all P. falciparum strains 260 . The interaction of a complex of P. falciparum proteins (reticulocyte-binding protein homologue 5 (PfRH5), PfRH5-interacting protein (PfRipr) and cysteine-rich protective antigen (PfCyRPA)) with basigin on the red blood cell surface is also essential for the invasion in all strains 261 , 262 . PfRH5 has been studied as a potential vaccine candidate 46 , and antibodies against basigin have been considered as a potential therapeutic strategy 263 . During the PfRH5–PfRipr–PfCyRPA–basigin binding step, an opening forms between the parasite and the red blood cell, and this triggers Ca 2+ release and enables parasite-released proteins to be inserted into the red blood cell membrane. These proteins are secreted from the micronemes (the small secretory organelles that cluster at the apical end of the merozoite) and from the neck of the rhoptries, and include rhoptry neck protein 2 (PfRON2). Binding between PfRON2 and apical membrane antigen 1 (PfAMA1) on the merozoite surface is required to mediate tight junction formation before the internalization process 264 , and PfAMA1 is also being evaluated as a vaccine candidate 265 . Parasite replication within the red blood cell requires the synthesis of DNA, which can be blocked by several antimalarials: pyrimethamine (PYR), P218 and cycloguanil target P. falciparum dihydrofolate reductase (PfDHFR) 266 , and atovaquone (ATO) blocks pyrimidine biosynthesis by inhibiting the expression of the mitochondrial gene pfcytb (which encodes P. falciparum cytochrome b ) and by preventing the formation of oxidized coenzyme Q, which is needed to enable the pyrimidine biosynthetic enzyme dihydroorotate dehydrogenase (PfDHODH) to perform its reaction within the mitochondria 50 . The phase II clinical candidate DSM265 also blocks pyrimidine biosynthesis by directly inhibiting PfDHODH 186 . In addition to DNA synthesis, other processes can be targeted by antimalarial drugs. Chloroquine (CHQ) inhibits haem polymerization in the food vacuole 52 but can be expelled from this compartment by the P. falciparum chloroquine-resistance transporter (PfCRT) 267 . The phase II clinical candidate KAE609 and the preclinical candidate SJ(557)733 both inhibit P. falciparum p-type ATPase 4 (PfATP4), which is required for Na + homeostasis during nutrient acquisition 57 , 183 , 184 . The phase I clinical candidate MMV(390)048 (Ref. 191 ) inhibits P. falciparum phosphatidylinositol 4-kinase (PfPI(4)K), which is required for the generation of transport vesicles that are needed to promote membrane alterations during ingression 58 . Hb, haemoglobin.

Replication . Once Plasmodium spp. gain entry into the red blood cell, they export hundreds of proteins into the host cell cytoplasm and cell surface that modulate the acquisition of nutrients, cell adhesion and sequestration in tissues, and pathogenesis 3 , 48 , 49 . Molecular and cell biology approaches are expanding our understanding of the molecular machinery that is required for the export, as well as the identification and function of the exported proteins.

In the red blood cell, Plasmodium spp. replicate rapidly, and during symptomatic disease the parasites may replicate exponentially to >10 12 parasites per patient. This rapid growth requires sustained pools of nucleotides for the synthesis of DNA and RNA, and as a consequence, many antimalarials target pyrimidine biosynthesis 50 ( Fig. 3 ). Plasmodium spp. are auxotrophic for all of the amino acids they need (that is, they must acquire all of these from food because they cannot synthesize them from precursors). Haemoglobin digestion (in a specialized food vacuole) supplies all amino acids except isoleucine, which must be obtained from other host cell components 51 . Haemoglobin digestion also releases haem, which is toxic to the parasite and, therefore, is polymerized into haemozoin (often called malaria pigment, which is visible as a blue pigment under light microscopy), which is an insoluble crystal that sequesters the toxic metabolite 52 . How haem polymerization is facilitated by the parasite remains unclear. A complex of several proteases and haem detoxification protein (HDP) have been identified in the food vacuole; follow-up in vitro studies have shown that components of this complex (for example, falcipain 2, HDP and lipids) were able to catalyse the conversion of haem into haemozoin 53 . The importance of understanding this mechanism is highlighted by the finding that chloroquine and other antimalarials act by inhibiting haem polymerization 54 ( Fig. 3 ). There is also evidence that the iron (haem-bound or free) liberated in the food vacuole during haemoglobin digestion plays a part in activating the toxicity to the parasite of artemisinin derivatives 42 .

Nutrient uptake by the parasite is coupled to the detrimental accumulation of Na + ; however, the parasite expresses an essential plasma membrane Na + export pump (the cation ATPase P. falciparum p-type ATPase 4 (PfATP4)) that can maintain Na + homeostasis 55 – 57 ( Fig. 3 ). The remodelling of the plasma membrane (membrane ingression) to generate daughter merozoites in the late schizont stage requires P. falciparum phosphatidylinositol 4-kinase (PfPI(4)K) 58 . Both PfPI(4)K and PfATP4 are targets of new drugs that are under development ( Fig. 3 ).

Immune evasion and host immunity

Malaria parasites first encounter the host immune system when sporozoites are injected in the skin (measured to be ∼ 15 per mosquito bite in one study 59 ), where they may be phagocytosed by dendritic cells for antigen presentation in the lymph node draining the skin inoculation site 60 . The chances of transmission are increased when the host is bitten by mosquitoes that carry a larger number of sporozoites, despite the fact that the number of sporozoites that can simultaneously pass through the mosquito's proximal duct is limited by the duct diameter 61 . Sporozoites encounter several other effectors of the immune system, and how a minority of them can reach the liver and infect the hepatocytes is not well understood. Immune evasion in the liver could be in part explained by the ability of sporozoites to suppress the function of Kupffer cells (also known as stellate macrophages, which are the resident macrophages of the liver) and repress the expression of genes that encode MHC class I molecules 62 . Our understanding of the host immunity associated with the red blood cell stage is more complete. Virulence genes in Plasmodium spp. are part of large expanded multigene families that are found in specialized (for example, subtelomeric) regions of the chromosomes 7 , 63 , 64 . These gene families (for example, var genes in P. falciparum ) encode variants of cell surface proteins that function in immune evasion through antigenic variation and also are involved in mediating cytoadherence of infected red blood cells to endothelial cells, which leads to red blood cell sequestration in tissues.

Malaria disease severity — in terms of both parasite burden and the risk of complicated malaria — is dependent on the levels of protective immunity acquired by the human host 65 – 67 , which can help to decrease the severity of symptoms and reduce the risk of severe malaria. Immunity is thought to result from circulating IgG antibodies against surface proteins on sporozoites (thereby blocking hepatocyte invasion) and merozoites (thereby blocking red blood cell invasion). In high-transmission areas where malaria is prevalent year-round, adults develop partially protective immunity. Young infants (<6 months of age) are also afforded some protection, probably from the antibodies acquired from their mother, whereas children from 6 months to 5 years of age have the lowest levels of protective immunity and are the most susceptible to developing high parasitaemia with risks for complications and death (for example, see the study conducted in Kilifi, Kenya 68 ). In low-transmission areas or areas that have seasonal malaria, individuals develop lower levels of protective immunity and typically have worse symptomatic malaria upon infection. This correlation between protective immunity and malaria severity poses a challenge for successful malaria treatment programmes; as the number of infections and the transmission rates decrease, increasing numbers of patients will lose protective immunity and become susceptible to severe disease. The re-introduction of malaria in areas that had been malaria-free for many years could be devastating in the short term and, therefore, well-organized surveillance is required.

Pathogenesis

The predominant pathogenic mechanism is the haemolysis of Plasmodium spp.-infected red blood cells, which release parasites and malaria endotoxin — understood to be a complex of haemozoin and parasite DNA, which trigger Toll-like receptor 9 (TLR9), a nucleotide-sensing receptor involved in the host immune response against pathogens 69 — that leads to high levels of tumour necrosis factor (TNF) production and to clinical symptoms such as fever 70 – 72 . In addition, the membrane of infected red blood cells stiffens, and this loss of deformability contributes to the obstruction of capillaries, which has life-threatening consequences in severe malaria when vital organs are affected 73 .

Parasite factors that influence disease severity . Disease severity and pathogenesis are linked to surface proteins that are expressed by the parasite. In P. falciparum , a major surface antigen is encoded by the var gene family, which contains ∼ 60 members 7 , 11 , 63 , 64 . The majority of the var genes are classified into three subfamilies — A, B and C — on the basis of their genomic location and sequence: the B and C groups mediate binding to host cells via CD36 (also known as platelet glycoprotein 4), whereas the A group genes mediate non-CD36 binding interactions that have been linked to severe malaria, including cerebral malaria 7 , 64 . The var genes encode P. falciparum erythrocyte membrane protein 1 (PfEMP1), with the B and C groups accounting for >80% of PfEMP1 variants. PfEMP1 is the major protein involved in cytoadherence and mediates the binding of infected erythrocytes to the endothelial vasculature. In cerebral malaria, A group PfEMP1 variants mediate the binding of infected erythrocytes to endothelial protein C receptor (EPCR) and intercellular adhesion molecule 1 (ICAM1) in the brain, causing pathology 8 , 11 , 74 , 75 . However, our knowledge of the host cell receptors that are involved in interactions with the infected erythrocytes is probably incomplete. For example, thrombin — which regulates blood coagulation via vitamin K-dependent protein C — can cleave PfEMP1, thereby reversing and preventing the endothelial binding of infected erythrocytes 74 . In pregnancy, the expression of a specific PfEMP1 variant, variant surface antigen 2-CSA (VAR2CSA) — which is not encoded by one of the three main subfamilies — leads to an increased risk of placental malaria 7 , 64 ( Box 3 ).

High parasitaemia levels also seem to correlate with poor outcomes 7 , 75 , and the circulating levels of P. falciparum histidine-rich protein 2 (which is encoded by pfhrp2 ) have been used as a biomarker of parasitaemia that predicts the risks for microvascular obstruction and severe disease 76 . The brain pathology in children with severe malaria has recently been described in detail 77 .

Additionally, P. vivax does not express the same family of var genes that have been found to be strongly associated with endothelium binding and tissue sequestration, which drives severe disease in P. falciparum , and the ability of P. vivax to only invade reticulocytes leads to lower parasite levels 7 .

Host traits that influence disease severity . Malaria has exerted a strong selection pressure on the evolution of the human genome 78 , 79 . Some haemoglobin-encoding alleles that in homozygous genotypes cause severe blood disorders (such as thalassaemia, the earliest described example, and sickle cell disease) have been positively selected in populations living in malaria-endemic areas because heterozygous genotypes protect against malaria 80 . Other inherited haemoglobin abnormalities (for example, mutations affecting haemoglobin C and haemoglobin E) can also provide protection against malaria 81 .

In addition, genetic polymorphisms that affect proteins expressed by red blood cells or that lead to enzyme deficiencies can also be protective against severe disease. The red blood cell Duffy antigen is a key receptor that mediates the invasion of P. vivax through interaction with the Duffy antigen-binding protein on the parasite surface 46 . The genetic inheritance of mutations in ACKR1 (which encodes the Duffy antigen) in Africa is credited with reducing the spread of P. vivax in this continent, although the finding of Duffy antigen-negative individuals who can be infected with P. vivax suggests that we still have an incomplete understanding of the factors involved in P. vivax invasion 82 , 83 . Glucose-6-phosphate dehydrogenase (G6PD) deficiency 78 , 79 provides protection against severe malaria through an unknown mechanism, at least in hemizygous males 84 , but unfortunately also leads to haemolytic anaemia in patients treated with primaquine, which is an 8-aminoquinoline antimalarial and the only agent currently approved for the treatment of latent (liver-stage) P. vivax malaria. The mode of action of primaquine, which is a prodrug, remains unknown.

The mechanisms of malaria protection in these varied genetic disorders have been widely studied 81 . Common findings include increased phagocytosis and elimination by the spleen of infected mutant erythrocytes, which reduces parasitaemia; reduced parasite invasion of mutant red blood cells; reduced intracellular growth rates; and reduced cytoadherence of infected mutant red blood cells. All of these effects increase protection against severe malaria, which is the main driver of human evolution in this case. Some point mutations in the gene that encodes haemoglobin alter the display of PfEMP1 on the surface of infected red blood cells, thereby diminishing cytoadherence to endothelial cells 85 , 86 . This finding highlights the crucial role of cytoadherence in promoting severe disease.

Finally, variability in the response to TNF, which is secreted from almost all tissues in response to malaria endotoxins, has also been proposed as a factor that mediates differential host responses and contributes to severe malaria when levels are high 7 .

Diagnosis, screening and prevention

The WHO criteria for the diagnosis of malaria consider two key aspects of the disease pathology: fever and the presence of parasites 87 . Parasites can be detected upon light microscopic examination of a blood smear ( Fig. 4 ) or by a rapid diagnostic test (RDT) 87 . The patient's risk of exposure (for example, whether the patient lives in an endemic region or their travel history) can assist in making the diagnosis. Furthermore, the clinical expression of Plasmodium spp. infection correlates with the species’ level of transmission in the area. The symptoms of uncomplicated malaria include sustained episodes of high fever ( Box 1 ); when high levels of parasitaemia are reached, several life-threatening complications might occur (severe malaria) ( Box 1 ).

Thin blood films showing Plasmodium falciparum (upper panel) and Plasmodium vivax (lower panel) at different stages of blood-stage development. The images are from methanol-fixed thin films that were stained for 30 minutes in 5% Giemsa. The samples were taken from Thai and Korean patients with malaria: Ethical Review Committee for Research in Human Subjects, Ministry of Public Health, Thailand (reference no. 4/2549, 6 February 2006). The sex symbols represent microgametes (male symbol) and macrogametes (female symbol). ER, early ring stage; ES, early schizont stage; ET, early trophozoite stage; FM, free merozoites; LR, late ring stage; LS, late schizont stage; LT, late trophozoite stage; U, uninfected red blood cell. The slides used were from a previously published study 268 but the images shown have not been previously published. Images courtesy of A.-R. Eruera and B. Russell, University of Otago, New Zealand.

The complications of severe malaria mostly relate to the blocking of blood vessels by infected red blood cells, with the severity and symptoms depending on what organ is affected ( Box 1 ) and to what extent, and differ by age; lung and kidney disease are unusual in children in Africa but are common in non-immune adults.

Parasitaemia . Patients with uncomplicated malaria typically have parasitaemia in the range of 1,000–50,000 parasites per microlitre of blood (however, non-immune travellers and young children who have parasite numbers <1,000 can also present with symptoms). The higher numbers tend to be associated with severe malaria, but the correlation is imprecise and there is no cut-off density. In a pooled analysis of patient data from 61 studies that were designed to measure the efficacy of ACTs (throughout 1998–2012), parasitaemia averaged ∼ 4,000 parasites per microlitre in South America, ∼ 10,000 parasites per microlitre in Asia and ∼ 20,000 parasites per microlitre in Africa 88 . The limit of detection by thick-smear microscopy is ∼ 50 parasites per microlitre 89 . WHO-validated RDTs can detect 50–1,000 parasites per microlitre with high specificity, but many lack sensitivity, especially when compared with PCR-based methods 90 . The ability to detect low levels of parasitaemia is important for predicting clinical relapses, as parasitaemia can increase 20-fold over a 48-hour cycle period. These data are based on measurements in healthy volunteers (controlled human infection models) who were infected at a defined time point with a known number or parasites, and in whom the asymptomatic parasite reproduction was monitored by quantitative PCR up to the point at which the individual received rescue treatment 91 .

In hyperendemic areas (with year-round disease transmission), often many children and adults are asymptomatic carriers of the parasite. In these individuals, the immune system maintains parasites at equilibrium levels in a ‘tug-of-war’. However, parasitaemia in asymptomatic carriers can be extremely high, with reports of levels as high as 50,000 parasites per microlitre in a study of asymptomatic pregnant women (range: 80–55,400 parasites per microlitre) 92 . In addition to the obvious risks for such people, they represent a reservoir for infecting mosquitoes, leading to continued transmission. In clinical studies, the parasitaemia of asymptomatic carriers can be monitored using PCR-based methods, which can detect as few as 22 parasites per millilitre 93 . However, the detection of low-level parasitaemia in low-resource settings requires advanced technology. Loop-mediated isothermal amplification (LAMP) 94 is one promising approach. This type of PCR is fast (10 9 -fold amplification in 1 hour) and does not require thermal cycling, which reduces the requirement for expensive hardware. Versions of this method that do not require electricity are being developed 95 . Nucleic acid-based techniques such as LAMP and PCR-based methods also have the advantage that they can be used to detect multiple pathogens simultaneously and, in theory, identify drug-resistant strains 96 . This approach enables the accurate diagnosis of which Plasmodium spp. is involved, and in the future could lead to the development of multiplexed diagnostics that enable differential diagnosis of the causative pathogens (including bacteria and viruses) in patients who present with fever 97 .

RDTs . RDTs are based on the immunological detection of parasite antigens (such as lactate dehydrogenase (LDH) or histidine-rich protein 2) in the blood, have sensitivities comparable to that of light microscopy examination and have the advantage that they do not require extensive training of the user. These tests provide rapid diagnosis at a point-of-care level in resource-limited settings and can, therefore, substantially improve malaria control. However, occasionally, false-positive results from RDTs can be problematic because they could lead to the wrong perception that antimalarial medicines are ineffective. False-negative test results have been reportedly caused by pfhrp2 gene deletions in P. falciparum strains in South America 98 – 103 . Current data indicate that LDH-targeting RDTs are less sensitive for P. vivax than for P. falciparum 104 , and limited information on the sensitivity of these tests for the rarer species, such as P. ovale or P. malariae , is available. RDTs also offer a great opportunity to track malaria epidemiology; photos taken with mobile phones of the results of the tests can be uploaded to databases (even using cloud-based data architecture 105 ) and provide an automated collection of surveillance data 106 .

Prevention in vulnerable populations

The prevention of Plasmodium spp. infection can be accomplished by different means: vector control, chemoprevention and vaccines. Mosquito (vector) control methods include the following (from the broadest to the most targeted): the widespread use of insecticides, such as DDT campaigns; the use of larvicides; the destruction of breeding grounds (that is, draining marshes and other breeding reservoirs); indoor residual spraying with insecticides (that is, the application of residual insecticide inside dwellings, on walls, curtains or other surfaces); and the use of insecticide-treated bed nets. The use of endectocides has also been proposed; these drugs, such as ivermectin, kill or reduce the lifespan of mosquitoes that feed on individuals who have taken them 107 . However, this approach is still experimental; individuals would be taking drugs that have no direct benefit to themselves (as they do not directly prevent human illness), and so the level of safety data required for the registration of endectocides for this purpose will need to be substantial. Vector control approaches differ in terms of their efficacy, costs and the extent of their effect on the environment. Targeted approaches such as insecticide-treated bed nets have had a strong effect. Chemoprevention is an effective strategy that has been used to reduce malaria incidence in campaigns of seasonal malaria chemoprevention, in intermittent preventive treatment for children and pregnant women, and for mass drug administration 108 . Such antimalarials need to have an excellent safety profile as they are given to large numbers of healthy people. Vaccines excel in eradicating disease, but effective malaria vaccines are challenging because — unlike viruses and bacteria, against which effective vaccines have been developed — protist pathogens (such as Plasmodium spp.) are large-genome microorganisms that have evolved highly effective immune evasion strategies (such as encoding dozens or hundreds of cell surface protein variants). Nevertheless, the improved biotechnological arsenal to generate antigens and improved adjuvants could help to overcome these issues.

Vector control measures . The eradication of mosquitoes is no longer considered an option to eliminate malaria; however, changing the capacity of the vector reservoir has substantial effects on malaria incidence. Long-lasting insecticide-treated bed nets and indoor residual spraying have been calculated to be responsible for two-thirds of the malaria cases averted in Africa between 2000 and 2015 (Ref. 12 ). Today's favoured and more-focused vector control approach involves the use of fine-mazed, sturdy, long-lasting and wash-proof insecticide-treated bed nets 109 . The fabric of these nets is impregnated with an insecticide that maintains its efficacy after ≥20 standardized laboratory washes, and these nets have a 3-year recommended use. Insects are attracted by the person below the net but are killed as they touch the net. However, the efficacy of bed nets is threatened by several factors, including their inappropriate use (for example, for fishing purposes) and behavioural changes in the mosquitoes, which have also begun to bite during the day 110 . The main problem, however, is the increasing emergence of vector resistance to insecticides, especially pyrethroids 110 and, therefore, new insecticides with different modes of action are urgently needed. New insecticides have been identified by screening millions of compounds from the libraries of agrochemical companies, but even those at the most advanced stages of development are still 5–7 years from deployment (see the International Vector Control Consortium website ( http://www.ivcc.com ) and Ref. 111 ) ( Fig. 5 ). Few of these new insecticides are suitable for application in bed nets (because of high costs or unfavourable chemical properties), but some can be used for indoor residual spraying. New ways of deploying these molecules are also being developed, such as improved spraying technologies 112 , timed release to coincide with seasonal transmission and slow-release polymer-based wall linings 113 , 114 .

The categories of compounds that are currently under study are defined in the first column on the left; compounds belonging to these categories have advanced to phase I trials or later stages. New screening hits (developed by Syngenta, Bayer, Sumitomo and the Innovative Vector Control Consortium (IVCC)) are at early research stages and are not expected to be deployed until 2020–2022. Similarly, species-specific approaches to the biological control of mosquitoes are not expected to move forward before 2025. The main data source for this Figure was the IVCC; for the latest updates visit the IVCC website ( www.ivcc.com ). Note that not all compounds listed on the IVCC website are shown in this Figure. The dates reflect the expected deployment dates. AI, active ingredient; CS, capsule suspension; IRS, indoor residual spray; LLIN, long-lasting insecticidal mosquito net; LLIRS, long-lasting indoor residual spray; LSHTM, London School of Hygiene and Tropical Medicine (UK); PAMVERC, Pan-African Malaria Vector Research Consortium. *Clothianidin and chlorfenapyr.

Genetic approaches, fuelled by advances in the CRISPR–Cas9 gene editing technology, represent an exciting area of development for novel insect control strategies. There are currently two main approaches: population suppression, whereby mosquitoes are modified so that any progeny are sterile; and population alteration, whereby mosquitoes are modified so that the progeny are refractory to Plasmodium spp. infection 115 , 116 . Initial approaches to population suppression involved releasing sterile male insects 117 . These strategies have now been developed further, with the release of male insects carrying a dominant lethal gene that kills their progeny 118 , 119 . Gene drive systems can be used for both population suppression and population alteration. These systems use homing endonucleases, which are microbial enzymes that induce the lateral transfer of an intervening DNA sequence and can, therefore, convert a heterozygote individual into a homozygote. Homing endonucleases have been re-engineered to recognize mosquito genes 120 and can rapidly increase the frequency of desirable traits in a mosquito population 121 . Gene drive systems have now been used in feasibility studies to reduce the size of mosquito populations 122 or to make mosquitoes less able to transmit malaria-causing parasites 123 . Another approach is inspired by the finding that Aedes aegypti mosquitoes (the vector for Dengue, yellow fever and Zika viruses) infected with bacteria of the Wolbachia spp. (a parasite that naturally colonizes numerous species of insects) cannot transmit the Dengue virus to human hosts 124 . Symbiont Wolbachia spp. can be modified to make them deleterious to other parasites in the same host, and progress has been made in finding symbionts that can colonize Anopheles spp. mosquitoes 125 , 126 . Although all of the above approaches are very promising, they are still at a very early stage, and the environmental uncertainties associated with the widespread distribution of such technologies, as well as the complex regulatory requirements, provide additional hurdles that will need to be overcome.

Chemoprotection and chemoprevention . Chemoprotection describes the use of medicines (given at prophylactic doses) to temporarily protect subjects entering an area of high endemicity — historically, tourists and military personnel — and populations at risk from emergent epidemics, but is also being increasingly considered for individuals visiting areas that have recently become malaria-free. Chemoprevention, which is often used in the context of seasonal malaria, describes the use of medicines with demonstrated efficacy that are given regularly to large populations at full treatment doses (as some of the individuals treated will be asymptomatic carriers).

Currently, there are three ‘gold-standard’ alternatives for chemoprotection: daily atovaquone–proguanil, daily doxycycline and weekly mefloquine. Mefloquine is the current mainstay drug used to prevent the spread of multidrug-resistant Plasmodium spp. in the Greater Mekong subregion of Southeast Asia, despite having a ‘black box warning’ for psychiatric adverse events; however, an analysis of pooled data from 20,000 well-studied patients found that this risk was small (<12 cases per 10,000 treatments) 127 . An active search to find new medicines that could be useful in chemoprotection, in particular medicines that can be given weekly or even less frequently, is underway. One interesting possibility is the use of long-acting injectable intramuscular combination chemoprotectants, which, if effective, could easily compete with vaccination, if they provided protection with 3–4 injections per year. Such an approach (called pre-exposure prophylaxis) is being studied for HIV infection (which also poses major challenges to the development of an effective vaccine) 128 and may lead to the development of long-acting injectable drug formulations 129 produced as crystalline nanoparticles (to enhance water solubility) using the milling technique.

Chemoprevention generally refers to seasonal malaria chemoprevention campaigns, which target children <5 years of age 130 . In the Sahel region (the area just south of the Sahara Desert, where there are seasonal rains and a recurrent threat of malaria), seasonal malaria chemoprevention with a combination of sulfadoxine–pyrimethamine plus amodiaquine had a strong effect 131 – 135 , with a >80% reduction in the number of malaria cases among children and a >50% reduction in mortality 136 . Although these campaigns are operationally complex — as the treatment has to be given monthly — >20 million children have been protected between 2015 and 2016, at a cost of ∼ US$1 per treatment. A concern about seasonal malaria chemoprevention is the potential for a rebound effect of the disease. Rebound could occur if children lose immunity to malaria while receiving treatment that is later stopped because they reached the age limit, if campaigns are interrupted because of economic difficulties or social unrest (war), or if drug resistance develops. Owing to the presence of resistant strains, a different approach is needed in African areas south of the Equator 137 , and this led to trials of monthly 3-day courses of ACTs in seasonal chemoprevention 135 ; there is an increasing amount of literature on the impressive efficacy of dihydroartemisinin (DHA)–piperaquine to prevent malaria in high-risk groups 138 . To reduce the potential for the emergence of drug resistance, the WHO good practice standards state that, when possible, drugs used for chemoprevention should differ from the front-line treatment that is used in the same country or region 108 , which emphasizes the need for the development of multiple, new and diverse treatments to provide a wider range of options.

Finally, intermittent preventive treatment is also recommended to protect pregnant women in all malaria-endemic areas 108 ( Box 3 ).

Vaccines . Malaria, along with tuberculosis and HIV infection, is a disease in which all components of the immune response (both cellular, in particular, during the liver stage, and humoral, during the blood stage) are involved yet provide only partial protection, which means that developing an effective vaccine will be a challenge. The fact that adults living in high-transmission malarious areas acquire partial protective immunity indicates that vaccination is a possibility. As a consequence, parasite proteins targeted by natural immunity, such as the circumsporozoite protein (the most prominent surface antigen expressed by sporozoites), proteins expressed by merozoites and parasite antigens exposed on the surface of infected red blood cells 139 have been studied for their potential to be used in vaccine programmes 140 . However, experimental malaria vaccines tend to target specific parasite species and surface proteins, an approach that both restricts their use and provides scope for the emergence of resistance. Sustained exposure to malaria is needed to maintain natural protective immunity, which is otherwise lost within 3–5 years 141 , perhaps as a result of the clearance of circulating antibodies and the failure of memory B cells to develop into long-lived plasma B cells. Controlled human infection models 142 – 144 have started to provide a more precise understanding of the early cytokine and T cell responses in naive subjects, emphasizing the role of regulatory T cells in dampening the response against the parasite, which results in the exhaustion of T cells 145 . Vaccine development is currently focusing on using multiple antigens from different stages of the parasite life cycle. Future work will also need to focus on the nature of the immune response in humans and specifically the factors that lead to diminished T cell responses. New generations of adjuvants are needed, possibly compounds that produce the desired specific response rather than inducing general immune stimulation. This is a challenging area of research, as adjuvants often have a completely different efficacy in humans compared with in preclinical animal models.

Currently, there is no vaccine deployed against malaria. The ideal vaccine should protect against both P. falciparum and P. vivax , with a protective, lasting efficacy of at least 75%. The most advanced candidate is RTS,S (trade name: Mosquirix; developed by GlaxoSmithKline and the Program for Appropriate Technology in Health Malaria Vaccine Initiative), which contains a recombinant protein with parts of the P. falciparum circumsporozoite protein combined with the hepatitis B virus surface antigen and a proprietary adjuvant. RTS,S reduced the number of malaria cases by half in 4,358 children 5–17 months of age during the first year following vaccination 146 , preventing 1,774 cases for every 1,000 children also owing to herd immunity, and had an efficacy of 40% over the entire 48 months of follow-up in children who received four vaccine doses over a 4-year period 147 . The efficacy of RTS,S during the entire follow-up period dropped to 26% when children only received three vaccine doses. The efficacy during the first year in 6–12-week-old children was limited to 33%. Thus, the RTS,S vaccine failed to provide long-term protection. Further studies, as requested by the WHO, will be done in pilot implementations of 720,000 children in Ghana, Kenya and Malawi (240,000 in each country, half of whom will receive the vaccine) before a final policy recommendation is made. However, a vaccine with only partial and short-term efficacy could still be used in the fight against malaria. RTS,S could be combined with chemoprevention to interrupt malaria transmission in low-endemic areas 148 . Thus, vaccines that are unable to prevent Plasmodium spp. infection could be used to prevent transmission (for example, by targeting gametocytes) or used as an additional protective measure in pregnant women.

A large pipeline of vaccine candidates is under evaluation ( Fig. 6 ). These include irradiated sporozoites — an approach that maximizes the variety of antigens exposed 149 — and subunit vaccines, which could be developed into multicomponent, multistage and multi-antigen formulations 150 . Although vaccines are typically designed for children, as the malaria map shrinks, both paediatric and adult populations living in newly malaria-free zones will need protection because they would probably lose any naturally acquired immunity and would, therefore, be more susceptible. Indeed, in recent years, there has been a focus on developing transmission-blocking vaccines to drive malaria elimination. This approach has been labelled altruistic, as vaccination would have no direct benefit for the person receiving it, but it would benefit the community; a regulatory pathway for such a novel approach has been proposed 151 , 152 . The most clinically advanced vaccine candidate that is based on this approach is a conjugate vaccine that targets the female gametocyte marker Pfs25 (Ref. 153 ), and other antigens are being tested preclinically. Monoclonal antibodies are another potential tool to provide protection. Improvements in manufacturing and high-expressing cell lines are helping to overcome the major barrier to the use of monoclonal antibodies (high costs) 154 , and improvements in potency and pharmacokinetics are reducing the volume and frequency of administration 155 . Monoclonal antibodies could be particularly useful to safely provide the relatively short-term protection needed in pregnancy. The molecular basis of the interaction between parasites and the placenta is quite well understood; two phase I trials of vaccines that are based on the VAR2CSA antigen are under way 156 , 157 .

The main data source for this Figure was Ref. 269 . Not all vaccines under development are shown in the Figure. AIMV VLP, Alfalfa mosaic virus virus-like particle; AMA1, apical membrane antigen 1; AMANET, African Malaria Network Trust; ASH, Albert Schweitzer Hospital (Gabon); ChAd63, chimpanzee adenovirus 63; CHUV, Centre Hospitalier Universitaire Vaudois (Switzerland); CNRFP, Centre National de Recherche et de Formation sur le Paludisme (Burkina Faso); CS, circumsporozoite protein; CSP, circumsporozoite protein; EBA, erythrocyte-binding antigen; ee, elimination eradication; EP, electroporation; EPA, Pseudomonas aeruginosa exoprotein A; EVI, European Vaccine Initiative; CVac, chemoprophylaxis vaccine; FhCMB, Fraunhofer Center for Molecular Biotechnology (USA); GSK, GlaxoSmithKline; IP, Institut Pasteur (France); INSERM, Institut National de la Santé et de la Recherche Médicale (France); JHU, Johns Hopkins University (USA); KCMC, Kilimanjaro Christian Medical College (Tanzania); KMRI, Kenyan Medical Research Institute; LSHTM, London School of Hygiene and Tropical Medicine (UK); M3V.Ad.PfCA, multi-antigen, multistage, adenovirus-vectored vaccine expressing Plasmodium falciparum CSP and AMA1 antigens; mAb, monoclonal antibody; ME-TRAP multiple epitope thrombospondin-related adhesion protein; MRCG, Medical Research Council (The Gambia); MSP, merozoite surface protein; MVA, modified vaccinia virus Ankara; MUK, Makerere University Kampala (Uganda); NHRC, Navrongo Health Research Centre (Ghana); NIAID, National Institute of Allergy and Infectious Diseases (USA); NIMR, National Institute for Medical Research (UK); NMRC, Naval Medical Research Center (USA); PAMCPH, pregnancy-associated malaria Copenhagen; PATH, Program for Appropriate Technology in Health; PfAMA1-DiCo, diversity-covering Plasmodium falciparum AMA1; PfCelTOS, Plasmodium falciparum cell-traversal protein for ookinetes and sporozoites; PfPEBS, Plasmodium falciparum pre-erythrocytic and blood stage; PfSPZ, Plasmodium falciparum sporozoite; PfSPZ-GA1, genetically attenuated PfSPZ; pp, paediatric prevention; PRIMALVAC, PRIMVAC project (INSERM); PRIMVAC, recombinant var2CSA protein as vaccine candidate for placental malaria; Pfs25, Plasmodium falciparum 25 kDa ookinete surface antigen; PvCSP, Plasmodium vivax circumsporozoite protein; PvDBP, Plasmodium vivax Duffy-binding protein; Rh or RH, reticulocyte-binding protein homologue; SAPN, self-assembling protein nanoparticle; SSI, Statens Serum Institut (Denmark); U., University; UCAP, Université Cheikh Anta Diop (Senegal); UKT, Institute of Tropical Medicine, University of Tübingen (Germany); USAMMRC, US Army Medical Research and Materiel Command; WEHI, Walter and Eliza Hall Institute of Medical Research (Australia); WRAIR, Walter Reed Army Institute of Research (USA). *Sponsors of late-stage clinical trials. ‡ Pending review or approval by WHO prequalification, or by regulatory bodies who are members or observers of the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH).

No single drug is ideal against all Plasmodium spp. or all of the manifestations of the disease that occur in different patient populations. Thus, treatment must be tailored to each situation appropriately 108 , 158 . First, the treatment of uncomplicated malaria and that of severe malaria are distinct. In uncomplicated malaria, the treatment of choice is an oral medicine with high efficacy and a low adverse-effect profile. However, the preferred initial therapy in severe malaria requires rapid onset and includes the parenteral administration of an artemisinin derivative, which can rapidly clear the parasites from the blood, and it is also suitable for those patients who have changes in mental status (such as coma) that make swallowing oral medications impossible. For the treatment of malaria during pregnancy, the options are limited to the drugs that are known to be safe for both the expectant mother and the fetus, and different regimens are needed ( Box 2 ). Different drugs are used for different Plasmodium spp., and the choice is usually driven more by drug resistance frequencies (which are lower in P. vivax , P. ovale , P. malariae and P. knowlesi than in P. falciparum ) than by species differences as such. Thus, chloroquine, with its low cost and excellent safety, is used in most cases of non- P. falciparum malaria, where it remains effective, whereas P. falciparum malaria requires newer medicines that overcome resistance issues. The persistence of P. vivax and P. ovale hypnozoites, even after clearance of the stages that cause symptoms, necessitates additional treatments. Only primaquine targets hypnozoites.

P. falciparum malaria

The mainstay treatments for uncomplicated P. falciparum malaria are ACTs: fixed-dose combinations of two drugs, an artemisinin derivative and a quinine derivative 108 ( Box 4 ; Table 1 ).

Owing to its high lipophilicity, artemisinin itself is not the molecule of choice in any stringent regulatory authority-approved combination. Instead, semisynthetic derivatives are used: namely, DHA (the reduced hemiacetal of the major active metabolite of many artemisinin derivatives), artesunate (a succinate prodrug of DHA that is highly water-soluble) or artemether (a methylether prodrug of DHA).

Quinine has been used in medicine for centuries 159 , but it was only in the mid-20th century that a synthetic form was made and the emerging pharmaceutical and government research sectors delivered the next-generation medicines that built on it. The combination partners of choice are 4-aminoquinolines (for example, amodiaquine, piperaquine and pyronaridine) and amino-alcohols (such as mefloquine or lumefantrine); these molecules are believed to interfere with haemozoin formation. There are now five ACTs that have been approved or are close to approval by the FDA, the European Medicines Agency (EMA) or WHO prequalification ( Figs 7 , 8 ; Table 1 ). In pivotal clinical studies, these combinations have proven extremely effective (achieving an adequate clinical and parasitological response (that is, the absence of parasitaemia at day 28 in >94% of patients; for example, see Ref. 160 ), are well-tolerated (as they have been given to >300 million paediatric patients), are affordable (typically under US$1 per dose) and, thanks to ingenious formulations and packaging, are stable in tropical climate conditions.

a | Preclinical candidates. b | Compounds or compound combinations that are in clinical development. The multitude of molecules that target only the asexual blood stages reflects the fact that many of these compounds are at an early stage of development, and further assessment of their Target Candidate Profile is still ongoing. KAF156 and KAE609 were discovered in a multiparty collaboration between the Novartis Institute for Tropical Disease (Singapore), the Genomics Institute of the Novartis Research Foundation (GNF; USA), the Swiss Tropical and Public Health Institute, the Biomedical Primate Research Centre (The Netherlands), the Wellcome Trust (UK) and Medicines for Malaria Venture (MMV). DSM265 was discovered through a collaboration involving the University of Texas Southwestern (UTSW; USA), the University of Washington (UW; USA), Monash University (Australia), GlaxoSmithKline (GSK) and MMV. MMV(390)048 was discovered through a collaboration involving the University of Cape Town (UCT; South Africa), the Swiss Tropical and Public Health Institute, Monash University, Syngene and MMV. SJ(557)733 was discovered in a collaboration involving St Jude Children's Research Hospital (USA), Rutgers University (USA), Monash University and MMV. Note that not all compounds are shown in this Figure, and updates can be found on the MMV website ( www.mmv.org) . CDRI, Central Drug Research Institute (India); ITM, Institute of Tropical Medicine; MRC, Medical Research Council; HKUST, Hong Kong University of Science and Technology; U., University. *Part of a combination that aims to be a new single-exposure radical cure (Target Product Profile 1). ‡ Product that targets the prevention of relapse in Plasmodium vivax malaria. § 3-day cure, artemisinin-based combination therapy. || Severe malaria and pre-referral treatment.

See the Medicines for Malaria Venture (MMV) website ( www.mmv.org ) for updates. CDRI, Central Drug Research Institute (India); GSK, GlaxoSmithKline; ITM, Institute of Tropical Medicine; U., University; UCT, University of Cape Town (South Africa); UTSW, University of Texas Southwestern (USA); UW, University of Washington (USA). *Part of a combination that aims to be a new single-exposure radical cure (Target Product Profile 1). ‡ Product that targets the prevention of relapse in Plasmodium vivax malaria. § 3-day cure, artemisinin-based combination therapy.

Following the results of comprehensive studies in Africa and Asia, the injectable treatment of choice for severe P. falciparum malaria is artesunate 161 – 163 . In the United States, artesunate for intravenous use is available as an Investigational New Drug (IND) through the Centers for Disease Control and Prevention (CDC) malaria hotline and shows efficacies of >90% even in patients who are already unconscious 161 . Sometimes, however, in low-income countries, it is necessary to administer intravenous quinine or quinine while awaiting an artesunate supply. Suppositories of artesunate are in late-stage product development 164 and are already available in Africa as a pre-referral treatment to keep patients alive while they reach a health clinic.

Box 4: Artemisinin

Artemisinin (also known as qinghaosu in China; see the structure) is extracted from the leaves of the Artemisia annua plant.

Youyou Tu was recognized by the 2015 Nobel Prize committee for her contribution to medicine for the discovery of artemisinin, which she achieved by retrieving and following instructions from ancient Chinese texts 247 . Owing to the ability of artemisinin to rapidly reduce parasitaemia and fever, the effect that artemisinin and its derivatives has had on the management of malaria cannot be overstated; since their introduction in the 1970s and their subsequent wider implementation — which was possible particularly owing to the work of Nicholas White and colleagues 248 – 251 — millions of lives have been saved. These drugs seem to be activated by haem-derived iron, and their toxicity is probably mediated through the formation of reactive oxidative radicals 42 . Data indicate that they interfere with phosphatidylinositol-3-phosphate metabolism (which is thought to be involved in the trafficking of haemoglobin to the digestive vacuole 252 ) and provide possible mechanistic insights into the nature of clinically observed artemisinin resistance 253 .

P. vivax malaria

Chloroquine or ACTs are WHO-recommended for uncomplicated P. vivax malaria 108 (although chloroquine is no longer used in several countries, such as Indonesia). As chloroquine-resistant P. vivax is becoming increasingly widespread, particularly in Asia, the use of ACTs is increasing; although only artesunate–pyronaridine is approved for the treatment of blood-stage P. vivax malaria, the other ACTs are also effective and are used off-label. Relapses of P. vivax malaria present a problem in malaria control. Relapse frequencies differ among P. vivax strains; they are high (typically within 3 weeks) in all-year transmission areas, such as Papua New Guinea, but relapse occurs on average after 7 months in areas with a dry or winter season. Some P. vivax strains, such as the Moscow and North Korea strains, are not, in most cases, symptomatic at the time of first infection but become symptomatic only following reactivation of the hypnozoites 165 . Primaquine needs to be administered in addition to the primary treatment to prevent relapse and transmission, which can occur even years after the primary infection. Primaquine treatment, however, requires 14 days of treatment, has gastrointestinal adverse effects in some patients, and is contraindicated in pregnant women and in patients who are deficient in or express low levels of G6PD (as it can cause haemolysis). Tafenoquine 166 , a next-generation 8-aminoquinoline, is currently completing phase III clinical studies. As with patients receiving primaquine, patients receiving tafenoquine will still require an assessment of their G6PD enzyme activity to ensure safe use of the drug and to determine the optimal dose. In phase II studies, tafenoquine was shown to have an efficacy similar to that of primaquine but with a single dose only compared with the 7–14-day treatment with primaquine; higher patient compliance is expected to be a major benefit of a single-dose regimen. The ultimate elimination of P. vivax malaria will be dependent on the availability of safe and effective anti-relapse agents, and is, therefore, a major focus of the drug discovery community.

Drug resistance

The two drugs in ACTs have very different pharmacokinetic profiles in patients. The artemisinin components have a plasma half-life of only a few hours yet can reduce parasitaemia by three-to-four orders of magnitude. By contrast, the 4-aminoquinolines and amino-alcohols have long terminal half-lives (>4 days), providing cure (defined as an adequate clinical and parasitological response) and varying levels of post-treatment prophylaxis. The prolonged half-life of the non-artemisinin component of ACTs has raised concerns in the research community owing to the risk of drug resistance development. However, the effectiveness of the ACTs in rapidly reducing parasitaemia suggests that any emerging resistance has arisen largely as a result of poor clinical practice, including the use of artemisinin derivatives as monotherapy, a lack of patient compliance and substandard medicine quality (including counterfeits); these are all situations in which large numbers of parasites are exposed to a single active molecule 167 . However, resistance to piperaquine 168 and partial resistance to artemisinin 169 (which manifests as a reduced rate of parasite clearance rate rather than a shift in the half-maximal inhibitory concentration (IC 50 )) has been confirmed in the Greater Mekong subregion, as well as resistance to mefloquine and amodiaquine in various parts of the world 170 . Africa has so far been spared, but reports of treatment failure for either artemisinin 171 or ACT 172 in African isolates of P. falciparum have raised concerns. Thus, artemisinin-resistant Plasmodium spp. and insecticide-resistant mosquitoes are major threats to the progress that has been made in reducing the number of malaria-related deaths through current control programmes. It is important to emphasize that progress against malaria has historically been volatile; in many areas, the disease has re-emerged as the efficacy of old drugs has been lost in strains that developed resistance.

Many advances have been made in identifying genetic markers in Plasmodium spp. that correlate with resistance to clinically used drugs ( Table 2 ). These markers enable the research and medical communities to proactively survey parasite populations to make informed treatment choices. Cross-resistance profiles reveal reciprocity between 4-aminoquinolines and amino-alcohols (that is, parasites resistant to one class are also less sensitive to the other). In addition, a drug can exert two opposite selective pressures: one towards the selection of resistant mutants and the other towards the selection of strains that have increased sensitivity to a different drug, a phenomenon known as ‘inverse selective pressure’ (Refs 173 , 174 ). These findings support the introduction of treatment rotation or triple combination therapies as potential future options. Finally, the drug discovery and development pipeline is delivering not only new compounds that have novel modes of action and overcome known resistant strains but also chemicals that have the potential to be effective in a single dose, which could overcome compliance issues. Nevertheless, policymakers need to be on high alert to prevent or rapidly eliminate outbreaks of resistant strains, and to prioritize the development of new treatments.

The drug discovery and development pipeline

The most comprehensive antimalarial discovery portfolio has been developed by the not-for-profit product development partnership Medicines for Malaria Venture (MMV) in collaboration with its partners in both academia and the pharmaceutical industry, with support from donors (mainly government agencies and philanthropic foundations) ( Fig. 7 ). Promising compound series have been identified from three approaches: hypothesis-driven design to develop alternatives to marketed compounds (for example, synthetic peroxides such as ozonides); target-based screening and rational design (for example, screening of inhibitors of P. falciparum dihydroorotate dehydrogenase (PfDHODH)); and phenotypic screening 175 . Phenotypic screening has been the most successful approach to date, in terms of delivering preclinical candidates and identifying — through the sequencing of resistant mutants — novel molecular targets. However, with advances in the understanding of parasite biology and in molecular biology technology, target-based approaches will probably have a substantial role in coming years.

Two combinations — OZ439 (also known as artefenomel) with ferroquine (Sanofi and MMV) and KAF156 with lumefantrine (Novartis and MMV) — are about to begin phase IIb development to test the efficacy of single-dose cure and, in the case of KAF156–lumefantrine, also 2-day or 3-day cures. OZ439 is a fully synthetic peroxide for which sustained plasma exposure is achieved by a single oral dose in humans 176 , 177 ; the hope is that it could replace the three independent doses required for artemisinin derivatives. Ferroquine is a next-generation 4-aminoquinoline without cross-resistance to chloroquine, amodiaquine or piperaquine 178 , 179 . KAF156 is a novel imidazolopiperazine that has an unknown mechanism of action 180 – 182 , but its resistance marker — P. falciparum cyclic amine resistance locus ( pfcarl ) — seems to encode a transporter on the endoplasmic reticulum membrane of the parasite. Interestingly, whereas OZ439 and ferroquine principally affect the asexual blood stages, KAF156 also targets both the asexual liver stage and the sexual gametocyte stage and, therefore, could have an effect on transmission.

Two other compounds, KAE609 (also known as cipargamin 183 , 184 ) and DSM265 (Refs 185 – 188 ), are poised to begin phase IIb and are awaiting decisions on combination partners. KAE609 is a highly potent spiroindolone that provides parasite clearance in patients even more rapidly than peroxides; its assumed mode of action is the inhibition of PfATP4 ( Fig. 3 ), which is encoded by its resistance marker and is a transporter on the parasite plasma membrane that regulates Na + and H + homeostasis. Inhibition of this channel, which was identified through the sequencing of resistant mutants, increases Na + concentrations and pH, resulting in parasite swelling, rigidity and fragility, thereby contributing to host parasite clearance in the spleen in addition to intrinsic parasite killing. In addition, effects on cholesterol levels in the parasite plasma membrane have been noted that are also likely to contribute to parasite killing by leading to an increased rigidity that results in more rapid clearance in vivo 189 . DSM265 is a novel triazolopyrimidine that has both blood-stage and liver-stage activity, and that selectively inhibits PfDHODH ( Fig. 3 ). It was optimized for drug-like qualities from a compound that was identified from a high-throughput screen of a small-molecule library 186 , 190 . DSM265 maintains a serum concentration that is above its minimum parasiticidal concentration in humans for 8 days, and has shown efficacy in both treatment and chemoprotection models in human volunteers in phase Ib trials 185 , 188 .

Within phase I, new compounds are first assessed for safety and pharmacokinetics, and then for efficacy against the asexual blood or liver stages of Plasmodium spp. using a controlled human malaria infection model in healthy volunteers 144 . This model provides a rapid and cost-effective early proof of principle and, by modelling the concentration–response correlation, increases the accuracy of dose predictions for further clinical studies. The 2-aminopyridine MMV(390)048 (also known as MMV048 (Refs 191 , 192 )), SJ(557)733 (also known as (+)-SJ733 (Refs 57 , 193 )) and P218 (Ref. 194 ) are currently progressing through phase I. MMV(390)048 inhibits PfPI(4)K ( Fig. 3 ), and this inhibition affects the asexual liver and blood stages, as well as the sexual gametocyte stage. MMV(390)048 has good exposure in animal models 192 , suggesting that it could potentially be used in a single dose in combination with another drug. SJ(557)733, which is a dihydroisoquinoline, inhibits PfATP4 and is an alternative partner that has a completely different structure from that of KAE609, and it has excellent preclinical safety and development potential. P218 is currently being evaluated for testing in controlled human malaria infection cohorts.

A further eight compounds are undergoing active preclinical development 195 . Of these compounds, four are alternatives to the leading compounds that target established mechanisms: the aminopyrazole PA92 (also known as PA-21A092 (Ref. 196 )) and the thiotriazole GSK030 (also known as GSK3212030A) both target PfATP4; DSM421 (Ref. 197 ) is a triazolopyrimidine alternative to DSM265; and UCT943 (also known as MMV642943) 198 is an alternative to MMV(390)048. Three compounds show novel mechanisms of action or resistance markers: M5717 (also known as DDD498 or DDD107498 (Ref. 199 )) inhibits P. falciparum elongation factor 2 (and, therefore, protein synthesis) and has outstanding efficacy against all parasite life-cycle stages; MMV253 (also known as AZ13721412) 200 is a fast-acting triaminopyrimidine with a V-type ATPase as resistance marker; and AN13762 (also known as AN762) is a novel oxaborole 201 with a novel resistance marker. All of these compounds have been developed through collaborations with MMV.

The eighth compound in active preclinical development, led by Jacobus Pharmaceuticals, is JPC3210 (Ref. 202 ), which is a novel aminocresol that improves upon the historical candidate (WR194965) that was developed by the Walter Reed Army Institute of Research and tested in patients at the time of the development of mefloquine in the 1970s. JPC3210 has an unknown mechanism of action and has potent, long-lasting efficacy in preclinical models, suggesting its potential to be used in a single dose for both treatment and prophylaxis 202 .

Quality of life

Malaria is one among the diseases of poverty. The WHO website states the following: “There is general agreement that poverty not only increases the risk of ill health and vulnerability of people, it also has serious implications for the delivery of effective health-care such as reduced demand for services, lack of continuity or compliance in medical treatment, and increased transmission of infectious diseases” (Ref. 203 ). The socioeconomic burden of malaria is enormous, and although the disease predominantly affects children, it is a serious obstacle to a country's development and economy 204 . Malaria is responsible for annual expenses of billions of euros in some African countries 205 . In many endemic areas, each individual suffers multiple episodes of malaria per year, with each episode causing a loss of school time for children and work time for their parents and guardians. Despite the declining trends in malaria morbidity and mortality, the figures are still disconcertingly high for a disease that is entirely preventable and treatable 16 .

Malaria also has long-term detrimental effects on the non-health-related quality of life of the affected population; it intensifies poverty by limiting education opportunities, as it leads to absenteeism in schools and reduced productivity at work 16 . The effects of acute illness normally drive families to seek urgent attention, which may consist of self-medication, if the disease is familiar to the household. Yet, even an episode of uncomplicated malaria can be potentially fatal, owing to a delay in promptly accessing efficacious antimalarial drugs. As malaria is so familiar to many households, patients — especially children — may be presented late for early diagnosis and treatment in health facilities. Late presentation prolongs morbidity, increases the risk of severe malaria, and deprives the families of income through direct expenses and reduced productivity. Frequent disease episodes experienced in the endemic areas as well as their possible complications can negatively affect child growth and nutrition, shortening the lives of children and family members. The neurological consequences can affect a child's ability to learn and become a self-reliant adult 206 – 208 , as they often occur during an important brain growth phase, when brain areas involved in higher learning (such as planning, decision-making, self-awareness and social sensitivity) mature. Cognitive deficits occurring during the early education years affect the entire family, as they impair the ability of the child to contribute to the well-being of the family as they grow and put additional strain on the parents, who may sometimes have to care for a substantially disabled child and, later, a disabled adult 209 .

The agenda set by the WHO aims for malaria incidence and mortality to decrease by 90% over the next 15 years, with increasing numbers of countries that eliminate the disease 210 . Even if we achieve the ambitious goals set by the WHO, there will still be a child dying of malaria every 10 minutes in 2030. The ACTs are extraordinarily effective, and much of the disease burden could be reduced by the complete deployment and availability of these medicines. There are now two approved ACTs that are specifically designed (taste-masked and sweetened) for paediatric use.

However, the emergence of drug-resistant Plasmodium spp. and insecticide-resistant mosquitoes is a major concern. The first clinical reports of artemisinin resistance came from the Thai–Cambodian border region in the mid-2000s 211 . So far, resistant strains have not spread to Africa, and the severity of the malaria caused by artemisinin-resistant parasites is not different from that of disease caused by wild-type strains. However, if artemisinin derivatives became ineffective, no alternative first-line treatments would be available, as new therapies are still only in phase II clinical trials, and their safety and efficacy will need to be effectively assessed in the field before they can be deployed for widespread clinical use.

Diagnostics

Future diagnostics should address two main issues. First, new diagnostic tests would ideally be non-invasive and not require a blood sample. Many approaches have been piloted, including parasite antigen detection in saliva 212 or urine 213 , the detection of specific volatile chemicals in breath 214 , and direct non-invasive measurements of iron-rich haemozoin in skin blood vessels 215 . Second, diagnostic tests should be able to detect drug-resistant strains directly in the point-of-care setting, rather than in sentinel sites, to provide better treatment and generate more-detailed epidemiological maps 216 . A next-generation amplicon-sequencing method suitable for use in endemic countries would enable the high-throughput detection of genetic mutations in six P. falciparum genes that are associated with resistance to antimalarial drugs, including ACTs, chloroquine and sulfadoxine–pyrimethamine 217 .

Malaria challenges

In addition to the length of the process of discovering and developing new drugs, insecticides and vaccines, in malaria there is the hurdle of the delivery of these new compounds, which first need to obtain approval from all local regulatory authorities. There is a trend for harmonization of the approval requirements among different authorities, with an initiative involving several regional African organizations, for example, to review data on behalf of many countries, similarly to the EMA reviewing files on behalf of all of the European Union countries. These events are paving the way to shorten the time from the end of clinical studies to the day of large-scale deployment, when affected populations will start to reap the benefits.

The move towards elimination and eradication

High-content cellular assays have become available to test inhibitors of transmission and compounds that target hypnozoites 218 , 219 . Discovery efforts for treatment and chemoprotection combinations conform to the malaria Target Product Profiles — a planning tool for therapeutic candidates that is based on FDA guidelines — to ensure that what is delivered has clinical relevance. The MMV has defined 220 and updated 221 Target Candidate Profiles (TCPs), which define the attributes that are required for the ideal medicines and have proven invaluable in guiding single-molecule optimization and decision-making.

The current focus is moving beyond TCP1 (which includes molecules that clear asexual blood-stage parasitaemia); the goal is to deliver compounds that do not simply treat patients and control symptoms but that also have biological activity that disrupts the life cycle of the parasite and hence break the transmission cycle, a step that is necessary in the move towards elimination. Particular areas of interest are anti-relapse agents for P. vivax malaria (TCP3; compounds that target hypnozoites), compounds that kill hepatic schizonts (TCP4) and protect against the onset of symptoms, and gametocytocidal compounds to block transmission (TCP5). Future projects include work on long-lasting endectocides (TCP6), such as ivermectin 107 . The MMV Discovery Portfolio also includes alternative compounds to the clinical frontrunners, molecules with new mechanisms of action (which target, for example, N -myristoyltransferase 222 , coenzyme A biosynthesis 223 , phenylalanyl tRNA synthetase 224 , prolyl 225 tRNA synthetase, plasmepsin V 226 and the Q i site of cytochrome bc 1 (Ref. 227 )) and compounds that seem to be resistance-proof (at least in vitro ).

In conclusion, while much progress has been made towards reducing the burden of malaria, much work remains to be done if these gains are to bring lasting relief to those living under the threat of infection. Without a continued focus on developing new antimalarials and new approaches for diagnosis and vector control, malaria will continue to exert an unacceptable toll on people living in disease endemic areas.

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Acknowledgements

The authors thank R. Bryant, A. Hill, S. Rees and S. L. Hoffman for their help with the content of Figure 4 and Figure 6 , and S. Duparc for critical reading of the clinical sections of the manuscript.

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Introduction (M.A.P., J.N.B. and W.C.V.V.); Epidemiology (M.A.P. and W.C.V.V.); Mechanisms/pathophysiology (M.A.P.); Diagnosis, screening and prevention (M.A.P., J.N.B., R.H.v.H. and T.N.C.W.); Management (J.N.B., R.H.v.H. and T.N.C.W.); Quality of life (C.M.); Outlook (R.H.v.H. and T.N.C.W.); Overview of Primer (M.A.P.).

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T.N.C.W. is a non-executive director of Kymab in the United Kingdom. Kymab has programmes in malaria that are funded by the Bill & Melinda Gates Foundation. All other authors declare no competing interests.

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Leveraging innovation technologies to respond to malaria: a systematized literature review of emerging technologies

• Moredreck Chibi 1 ,
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Malaria Journal volume  22 , Article number:  40 ( 2023 ) Cite this article

In 2019, an estimated 409,000 people died of malaria and most of them were young children in sub-Saharan Africa. In a bid to combat malaria epidemics, several technological innovations that have contributed significantly to malaria response have been developed across the world. This paper presents a systematized review and identifies key technological innovations that have been developed worldwide targeting different areas of the malaria response, which include surveillance, microplanning, prevention, diagnosis and management.

A systematized literature review which involved a structured search of the malaria technological innovations followed by a quantitative and narrative description and synthesis of the innovations was carried out. The malaria technological innovations were electronically retrieved from scientific databases that include PubMed, Google Scholar, Scopus, IEEE and Science Direct. Additional innovations were found across grey sources such as the Google Play Store, Apple App Store and cooperate websites. This was done using keywords pertaining to different malaria response areas combined with the words “innovation or technology” in a search query. The search was conducted between July 2021 and December 2021. Drugs, vaccines, social programmes, and apps in non-English were excluded. The quality of technological innovations included was based on reported impact and an exclusion criterion set by the authors.

Out of over 1000 malaria innovations and programmes, only 650 key malaria technological innovations were considered for further review. There were web-based innovations (34%), mobile-based applications (28%), diagnostic tools and devices (25%), and drone-based technologies (13%.

Discussion and conclusion

This study was undertaken to unveil impactful and contextually relevant malaria innovations that can be adapted in Africa. This was in response to the existing knowledge gap about the comprehensive technological landscape for malaria response. The paper provides information that countries and key malaria control stakeholders can leverage with regards to adopting some of these technologies as part of the malaria response in their respective countries.

The paper has also highlighted key drivers including infrastructural requirements to foster development and scaling up of innovations. In order to stimulate development of innovations in Africa, countries should prioritize investment in infrastructure for information and communication technologies and also drone technologies. These should be accompanied by the right policies and incentive frameworks.

In sub-Saharan Africa, malaria is the leading cause of death for children under 5. It has been reported that malaria infection during pregnancy increases the risk of maternal mortality and neonatal mortality [ 1 ]. According to the World Health Organization (WHO), there were 229 million cases of malaria in 2019 compared to 228 million cases in 2018. The estimated number of malaria deaths stood at 409,000 in 2019, compared with 411,000 deaths in 2018. Children under 5 years of age are the most vulnerable group affected by malaria and in 2019 they accounted for 67% (274,000) of all malaria deaths worldwide. The WHO African Region continues to carry a disproportionately high share of the global malaria burden. In 2019, the region was home to 94% of all malaria cases and deaths with six countries accounting for approximately half of all malaria deaths worldwide: Nigeria (23%), the Democratic Republic of the Congo (11%), United Republic of Tanzania (5%), Burkina Faso (4%), Mozambique (4%) and Niger (4%) [ 2 ].

Knowledge, learning and innovation are key to addressing, minimizing and tackling these disparities. One example of this is the knowledge hub developed by WHO called MAGICapp which aims to give living evidence and resources for tackling malaria interventions. It contains all official WHO recommendations for malaria prevention (vector control and preventive chemotherapies) and case management (diagnosis and treatment). The resources serve as a guide on the strategic use of information to drive impact, surveillance, monitoring and evaluation; operational manuals, handbooks, and frameworks; and a glossary of key terms and definitions. So, this paper aligns with identifying and adding discourse into the importance of reviews especially from a technological perspective.

To understand the advances in malaria services, various scholars have undertaken reviews across vast thematic areas of malaria interventions. In a quest to inform policy, Garner et al. [ 3 ] conducted an analysis of why Cochrane Reviews are important in malaria interventions. They noted that it is important for researchers to collaborate across regions and in understanding new preventive interventions. Their aim was to inform policymakers to understand the importance of reviews in identification of trends that are occurring in malaria interventions. Other aspects that have been looked at through reviews are the costs and cost-effectiveness aligned with malaria control interventions. White et al. [ 4 ] looked at interventions from studies published between 2000 and 2010 looking at the role of infection detection technologies for malaria elimination and eradication and the costs related to them in order to assess how accessible interventions are across regions. More recently, Conteh et al. [ 5 ] also carried on with assessing the unit cost and cost-effectiveness of malaria control during the period of January 1, 2005, and August 31, 2018. The aim was to see how resource allocation can be planned proactively according to costs, though they did highlight that care in methodological and reporting standards is required to enhance data transferability.

In a bid to combat malaria epidemic, several technological innovations have been developed all over the world that have contributed significantly to malaria response. Adeola et al. [ 6 ] reviewed the use of spatial technology for malaria epidemiology in South Africa between 1930 and 2013. The focus was on the use of statistical and mathematical models as well as geographic information science (GIS) and remote sensing (RS) technology for malaria research to create a robust malaria warning system. The mathematical modelling is also aligned with agent-based modelling which Smith et al. [ 7 ] highlighted through their analysis of 90 articles published between 1998 and May 2018 characterizing agent-based models (ABMs) relevant to malaria transmission. The aim was to provide an overview of key approaches utilized in malaria prevention. Such technologies feed into modelling sites and interventions to project various outcomes. From a platform centric perspective, Vasiman et al. [ 8 ] analysed how different mobile phone devices and handheld microscopes work as diagnostic platforms for malaria in low-resource settings. Malaria diagnostics tests and methods have also been reviewed as being key in the successful control and elimination programmes [ 9 ]. Mobile health has been found to play a key role in supporting health workers in the diagnosis and treatment of malaria in sub-Saharan Africa [ 10 ].

To add to this discourse, this paper presents a holistic systematized review of key technological innovations that have been developed worldwide targeting different areas of the malaria response, which include surveillance, microplanning, prevention, diagnosis, and management. A systematized review was utilized in this study as data sources that included unconventional grey sources was utilized and the review gravitated more towards being narrative with tabular accompaniments as compared to the systematic literature reviews that are less narrative [ 11 ]. The study was undertaken with the view to provide African countries and key stakeholders with information relating to technologies that can be adapted in their different contexts as they strengthen malaria response strategies.

Scientific databases literature search

This study adopted a systematic search strategy to identify the publications with innovations related to malaria surveillance, microplanning, prevention, diagnosis, and management from 5 scientific databases (PubMed, Google Scholar, Scopus, IEEE and Science Direct). The keywords used were malaria surveillance, microplanning, prevention, diagnosis and management combined with the words “innovations” or “technologies” in a search query. Innovations deemed not relevant to the scope of this research by the authors include drugs, vaccines, social programmes. Only papers reporting design, implementation or evaluation of malaria technological innovations were considered in this paper. The process was shown in Fig.  1 . The quality of technological innovations included was based on reported impact and judgement by the authors.

PRISMA flow chart for the malaria innovations literature search

Search through technology platforms e.g., google play store and apple app store

This study also adopted a systematic search strategy to identify the mobile apps related to malaria surveillance, microplanning, prevention, diagnosis and management available in the Google Play and Apple App stores. Keywords such as malaria surveillance, microplanning, prevention, diagnosis, and management were used in the search. The search was conducted between July 2021 and December 2021. The applications had to have a description, be in English, have 1000 + installs and reviews to be included in the analysis. The applications that did not meet these criteria were excluded. The core research question was: What mobile-based innovations are available for malaria interventions that can be adopted by the countries in the WHO Africa region for use across the continuum of the malaria response ? The resultant apps considered for this study were 260 as shown in Fig.  2 .

PRISMA flow chart for the mobile apps

Web search using a custom web-content mining algorithm

A custom web-content mining algorithm was also developed to search for malaria innovations and technologies published on different cooperate organizational websites, social media channels like twitter, and media channels like legit news websites like CNN. These technological innovations were collated between July 2021 and December 2021. The innovation name, description, Intellectual Property owner, web link to the innovation and geographical location were collated. Innovations that did not have functional and tested prototypes and were not related to addressing malaria interventions were excluded. The number of innovations surpassed 1000 however after screening, only 240 key technological innovations were selected that best fit the selection criteria.

A total of 650 malaria innovations (260 from Google play and Apple App store, 150 from scientific databases and 240 from web content mining) were considered for detailed review.

The review has identified innovations for malaria in the following technological thematic areas; web-based innovations (34%), mobile-based applications (28%), diagnostic tools and other devices (25%), and drone-based technologies (13%).

Web-based innovations

The web-based technologies include GIS systems [ 12 ]. An example is the Malaria Atlas Project (MAP), developed at the Telethon Kids Institute, Perth, Western Australia. MAP is a web platform that displays time aware raster and survey point data for malaria incidence, endemicity, and mosquito distribution. MAP has been designated as a WHO Collaborating Centre in Geospatial Disease Modelling. The impact of the Atlas Project has been validated in Sokoto Nigeria by Nakakana et al. [ 13 ]. The study concluded that the prevalence of malaria and its transmission intensity in Sokoto are similar to the Malaria Atlas Project predictions for the area and that is essential in modellings various aspects of malaria control planning purposes.

Other innovations like malariaAtlas which is an open-access R-interface on the Malaria Atlas Project, collates malariometric data, providing reproducible means of accessing such data within a freely available and commonly used statistical software environment [ 14 ]. A team from the University of Queensland developed a GIS-based spatial decision support system (SDSS) used to automatically locate and map the distribution of confirmed malaria cases, rapidly classify active transmission foci, and guide targeted responses in elimination zones. This has been implemented and evaluated in the Solomon Islands and Vanuatu in a study by Kelly et al. [ 15 ] and 82.5% of confirmed malaria cases were automatically geo-referenced and mapped at the household level, with 100% of remaining cases geo-referenced at a village level using the system. The GIS-based spatial decision support system has also been implemented in other countries like Vietnam. In Korea, the Malaria Vulnerability Map Mobile System which consists of a system database construction, malaria risk calculation function, visual expression function, and website and mobile application has been developed for use in Incheon [ 16 ]. The Malaria Decision Analysis Support Tool (MDAST) project promotes evidence-based, multi-sectoral malaria control policy-making in Kenya, Tanzania, and Uganda, serving as a pilot for such a programme in other malaria-prone countries [ 17 ].

In Zanzibar, the Malaria Case Notification (MCN) System was developed and the performance evaluation of the tool by Khandekar [ 18 ] showed that while a surveillance system can automate data collection and reporting, its performance will still rely heavily on health worker performance, community acceptance, and infrastructure within a country. A study by Mody et al. [ 19 ] showed that the use of telemedicine and e-health technologies shows promise for the remote diagnosis of malaria and hence several systems been developed. ProMED Mail (PMM) is an open and free to use, global, e-health based surveillance system from the International Society for Infectious Diseases with several use cases for malaria [ 20 , 21 ]. The Epidemic Prognosis Incorporating Disease and Environmental Monitoring for Integrated Assessment (EPIDEMIA) computer system was designed and implemented to integrate disease surveillance with environmental monitoring in support of operational malaria forecasting in the Amhara region of Ethiopia [ 22 ]. Table 1 summarizes some of the technologies.

Mobile applications-based technologies

This study has also revealed that several mobile-based malaria innovations have been developed which include smart mobile apps, Short Message Service (SMS) based apps and Unstructured Supplementary Service Data (USSD) based applications for use across the continuum of the malaria response. In India the Mobile-based Surveillance Quest using IT (MoSQuIT) is being used to automate and streamline malaria surveillance for all stakeholders involved, from health workers in rural India to medical officers and public health decision-makers. Malaria Epidemic Early Detection System (MEEDS) is a groundbreaking mHealth system used in Zanzibar by health facilities to report new malaria cases through mobile phones. Coconut Surveillance is an open-source mobile software application designed by malaria experts specifically for malaria control and elimination and it has become an essential tool for the Zanzibar Malaria Elimination Programme [ 23 ]. The SMS for Life initiative is a ‘public-private’ project that harnesses everyday technology to eliminate stock-outs and improve access to essential medicines in sub-Saharan Africa with a health focus on malaria and other vector borne diseases. This has been implemented and evaluated in Tanzania [ 24 ]. In Mozambique Community Health Workers (CHWs) use inSCALE CommCare tool for decision support, immediate feedback and multimedia audio and images to improve adherence to protocols.

Additional surveillance apps include the likes of the DHS mobile app for Malaria Indicator Surveys and Solution for Community Health-workers (SOCH) mobile app is a comprehensive mobile application tool for disease surveillance, workforce management and supply chain management for malaria elimination [ 25 ]. The National Malaria Case-Based Reporting App (MCBR) is a mobile phone application for malaria case-based reporting to advance malaria surveillance in Myanmar [ 26 ]. Mobile apps have also been used to support distribution of medicines like the Net4Schs App, an android application that is used for data capturing, processing and reporting on School Long-lasting insecticidal nets (LLINs) distribution activities. Apps have also been developed to support malaria screening and diagnosis for example the NLM Malaria Screener is a diagnostic app that assists users in the diagnosis of malaria and in the monitoring of malaria patients. This has been validated in several studies and it is reported that it makes the screening process faster, more consistent, and less dependent on human expertise [ 27 ]. Additional diagnostic apps include the Malaria System MicroApp which is a mobile device-based tool for malaria diagnosis [ 28 ], the Malaria Hero app is a web based mobile app for diagnosis of malaria, and LifeLens is a smartphone app that can detect malaria. Some key technologies are summarized in Table 2 .

Other notable mobile apps that have also been used in malaria management include CommCare’s usage in in Mozambique for integrated community case management in the remote communities. This has been reported to strengthen Community-Based Health [ 29 ]. Another app, FeverTracker, has been used for malaria surveillance and patient information management in India. There has also been a number of educational and knowledge base apps. These are the likes of Malaria Consultant, a mobile application designed to educate individuals on malaria and its prevention; the WHO Malaria toolkit App that brings together the content of the latest world malaria report and of the consolidated WHO Guidelines for malaria. This includes operational manuals for carrying out malaria interventions and other technical documents in one easy to navigate resource. Another interesting area where mobile apps have been used is in malaria prevention and such apps include those that scare away mosquitoes using high frequency sounds, and these include Anti Mosquito Repellent Sound App.

Drone-based technologies

This review has revealed that drone technologies can greatly help in malaria control programmes. The drones can be used in developing genetically-based vector control tools [ 30 ], delivering massive aerial spraying to kill mosquito larvae [ 31 ], identifying mosquito larvae sites using aerial imaging [ 32 ] and in delivering drugs and vaccines [ 33 ]. Anti-malaria drones have been widely used to spray biological insecticides in rice fields and swamps to reduce the emerging mosquito populations. This has been successful in Kenya, Tanzania, India, Rwanda and Zanzibar. In Zanzibar, the Agras MG-1S drones were used to spray 10 L of a biodegradable agent called Aquatain; a chemical that has been used to cover drinking water basins. Drones have also been used to collect data to identify mosquito breeding sites so that the larvae can be controlled, reducing the number of adult mosquitoes able to spread malaria. For example in Malawi and near Lake Victoria the DJI Phantom low-cost drones are being used to survey and find mosquito breeding grounds. A new trial using ‘gene drive’ technology is currently taking place in Burkina Faso where the trial will see the release of genetically modified mosquitoes in an attempt to wipe out the female carriers of the disease [ 34 ].

Diagnostic tools including other devices developed for malaria interventions

Devices that have been developed to respond to malaria include the SolarMal device, a solar-powered mosquito trapper being piloted in Kenya [ 35 ]. The Solar Powered Mosquito Trap (SMOT) is baited with a synthetic odor blend that mimics human odor to lure host-seeking malaria mosquitoes. Other devices such as the ThermaCell Patio Shield Mosquito Repellants developed by ThermaCell are shield lanterns that repel mosquitoes by creating a 15-foot zone of protection. Several devices have also been developed to improve malaria diagnosis and these include the Nanomal DNA analyzer a simple, rapid and affordable point-of-care (POC) handheld diagnostic nanotechnology device to confirm malaria diagnosis and detect drug resistance in malaria parasites in minutes and at the patient’s side, by analysis of mutations in malaria DNA using a range of proven nanotechnologies. Medication Events Monitoring Device (MEMS) have also been greatly used to monitor medication adherence to malaria drugs [ 36 ]. Malaria Rapid Diagnostic Tests (RDTs), sometimes called dipsticks or Malaria Rapid Diagnostic Devices (MRDDS), are simple immunochromatographic tests that identify specific antigens of malaria parasites in whole or peripheral blood. They are categorized into dipstick, cassette or hybrids. Dipstick RDTs are cheap and readily available on market [ 37 ]. An example is the OptiMAL dipstick [ 38 ]. Cassette RDTS are complex and require much time for results to be read but are much safer to use.

This research has culminated into insightful conclusions from the systematized review of the malaria technological Innovations and has been the foundation of the collated database that can be accessed via the WHO AFRO marketplace platform. This is a platform that has been developed to showcase various technologies and innovations that can be applied for different disease areas. This focused on technologies relevant for malaria response. The identified intervention technologies and focus areas provide ways of identifying key leverage points in strengthening the health systems and making tangible impact towards various mandates to fight the scourge of malaria. More importantly highlighting these trends empowers innovators and policy makers on the continent to make informed decisions on applying frugal design to develop affordable, locally manufactured, functional and sustainable innovations fit for the African continent. Furthermore, the marketplace platform provides implementation insights to African nations on the adoption of some of the technological innovations from this study.

The review has highlighted that mobile applications are a vital component of malaria response programmes and are increasingly being used along the different response areas, such as surveillance (malaria data capturing apps like Coconut Surveillance and DHS mobile app), microplanning (drug delivery and distribution management apps like Net4Schs App), prevention (mosquito repelling like Anti Mosquito Repellent Sound App), diagnosis (AI driven slide analysis apps like LifeLens and Malaria Screener), management (telehealth like the Malaria Consultant) and the provision of support for health services [decision support like the solution for Community Health-workers (SOCH) app] as outlined in Fig.  3 . Their impact has been validated in several studies [ 27 , 39 ].

Analysis of the innovations by category, application and target outcome

In 2019, 93% of the global population was covered by a mobile broadband signal. In Sub-Saharan Africa, 3G coverage expanded to 75% compared to 63% in 2017, while 4G doubled to nearly 50% compared to 2017 [ 40 ]. This implies that mobile solutions can substantially mitigate many of the health system limitations prevalent mostly in African countries where malaria is endemic. A substantial number of mobile applications have been developed for surveillance of malaria control programs in Africa such as inSCALE (Mozambique), Coconut Surveillance (Zanzibar), CommCare (Senegal) and DHIS2 (Zimbabwe, and South Africa). This shows that mobile-based apps give a larger footprint and a high level of agility to malaria response. Nevertheless, limited connectivity and erratic energy supplies have been key factors affecting the levels of adoption and some apps have been reported to have a high level of complexity. This has also been reported in other studies [ 41 , 42 ].

Moreover, it has been noted that most of these apps are independent with limited capability for interoperability. Hence there is a need to develop open standards for mobile technologies for malaria control. For example, surveillance applications should be able to have geolocation capabilities and use exiting open-source platforms like OpenStreetMap, OpenDataKit & OpenMapKit; work online and offline mode to enable usage in resource constraints areas, ease of use to enable usage with little or no training and should support different languages including local languages. This calls for more research and implementation of natural language processing frameworks for use in mobile apps in Africa, which can assist with data analytics as well. Furthermore, aligning app development with standards such as the Fast Healthcare Interoperability Resources (FHIR) which facilitate interoperability between legacy health care systems and technology is important.

Superseding technological interoperability, there needs to be platform integration and overall visibility particularly on innovations that target malaria diagnosis, surveillance and management. However, it should be noted that systemically there has been launching of different applications for different malaria interventions which may confuse the public in terms of usage. Therefore, a single application or platform integrating several services such as Coconut Surveillance and owned and managed by a reputable malaria organization or the ministries of health may benefit citizens by allowing them to access services from a single and trusted application. Misinformation and misdiagnosis from publicly available medical apps is a health threat to the public as reported by [ 43 ].

Most of the reviewed web systems depend on data or are used to collect large amounts of malaria data to support decision-making. Hence a need for national malaria control and elimination information systems that can utilize regional and global structures, prioritizing cross-border intelligence sharing information regarding disease transmission hotspots, outbreaks, and human movement. Such systems can also be very useful in responding to pandemics like COVID-19 and other infectious outbreaks. There is also a need to have malaria related data centrally stored and managed by the Ministry of Health or malaria control programmes to guide decision-making at all levels of malaria response among the different stakeholders. Hospitals and clinics have also developed standalone patient information management systems in addition to the national health information management systems like OpenMRS and DHIS2. However, there is no communication between the different patient’s information management systems hence a need for development of open data standard driven systems and APIs to enforce interoperability among health systems in Africa. An effective information system must receive data from other sources, process it and send it back to other systems being used in malaria programme, particularly at the community level.

In malaria control, larval source management is very difficult to archive in rural areas due to perceived difficulties in identifying target areas [ 44 ]. Drones can capture extremely detailed images of the landscape, opening the possibility of replacing the time-consuming hunt for mosquito larvae on the ground with identifying habitat through aerial imagery. The review has shown that this has been used in several countries for example in Malawi and near Lake Victoria using DJI Phantom; low-cost drones that survey wilderness to find mosquito breeding grounds using Geospatial technology. Geospatial technology is rapidly evolving and now can be archived using remotely sensed data [ 45 ]. In Zanzibar, drones have been used to spray rice fields with a thin, non-toxic film as a strategy to eliminate mosquitoes. The review has shown that drones are a possible solution in malaria control programmes as also indicated in other studies [ 45 ,  46 ]. The review also showed that rapid diagnostics tools offer fast turnaround services while circumventing obstacles faced when using microscopy in peripheral health care settings, including cost of equipment, reagents, and the need for electricity and skilled personnel [ 47 ].

This study has reviewed key emerging technologies used in malaria control programmes. The review revealed various technological applications that have been developed in response to malaria including surveillance, microplanning, prevention, diagnosis and management. Although breakthrough innovative platforms have been made available, one key challenge remained, which is lack of integration of key end-to-end components and functionalities to facilitate effective and efficient malaria response and to reduce fragmentation.

The review has also revealed several stakeholders in malaria control hence a need for mechanisms that promote the exchange of evidence between scientific, policy, and programme management communities for analysing the potential outcomes of the different malaria control strategies and interventions. In many malaria-endemic areas in Africa, the communication gap between policy makers, health workers, and patients is a significant barrier to efficient malaria control.

Furthermore, artificial intelligence (AI) has been widely used in the reviewed technological innovations, however there is an urgent need to provide reliable datasets, develop local AI expertise among WHO African member states, implement data protection and privacy acts; and put in place health innovation clusters to bring the different stakeholders together to develop and adopt appropriate technologies to solve the intended challenges.

Limitations of this work and future prospects

The main limitation of this work was that some applications were overlapping among the response areas and hence the decision to place an innovation under a given category was based on the judgement of the authors. Another limitation is the fact that this work is not aimed at analysing the total landscape of all malaria innovations. Only those that met the inclusion criteria and deemed relevant by the authors were included hence some innovations might not have been captured but we will be subjected to continuous update on the global database for malaria innovations at https://innov.afro.who.int/emerging-technological-innovations/7-malaria-innovations . Future research can focus on reviewing the technologies that are open source dedicated to malaria, and publishing findings that can be used by medical practitioners, application developers, and governments to collaborate in the process of containing the spread of malaria.

Availability of data and materials

The data used in this report is available to readers.

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Chibi, M., Wasswa, W., Ngongoni, C. et al. Leveraging innovation technologies to respond to malaria: a systematized literature review of emerging technologies. Malar J 22 , 40 (2023). https://doi.org/10.1186/s12936-023-04454-0

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• Volume 14, Issue 8
• Comprehensive evaluation of malaria reactive surveillance and response strategies in Lao People’s Democratic Republic: a mixed-methods study
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• http://orcid.org/0000-0003-2820-477X Win Htike 1 , 2 ,
• Win Han Oo 3 , 4 ,
• http://orcid.org/0000-0001-6821-859X Nilar Aye Tun 4 ,
• Boualam Khamlome 5 ,
• Phoutnalong Vilay 5 ,
• Virasack Banouvong 5 ,
• Keobouphaphone Chindavongsa 5 ,
• Thet Lynn 6 ,
• Sanya Vathanakoune 6 ,
• May Chan Oo 1 ,
• Ei Phyu Htwe 1 ,
• Aung Khine Zaw 1 ,
• http://orcid.org/0000-0003-1746-8083 Kaung Myat Thu 1 ,
• Naw Hkawng Galau 1 ,
• Kaung Myat Khant 3 ,
• Julia C Cutts 3 ,
• Paul A Agius 3 , 7 ,
• Ellen Kearney 3 , 4 ,
• Katherine O’Flaherty 3 , 4 ,
• http://orcid.org/0000-0001-5832-9464 Freya J I Fowkes 3 , 4
• 1 Health Security Program , Burnet Institute Myanmar , Yangon , Myanmar
• 2 School of Medicine, Faculty of Health , Deakin University , Burwood , Victoria , Australia
• 3 Disease Elimination Program , Burnet Institute , Melbourne , Victoria , Australia
• 4 The University of Melbourne School of Population and Global Health , Melbourne , Victoria , Australia
• 5 Centre of Malariology, Parasitology and Entomology , Vientiane , Lao People's Democratic Republic
• 6 Health Poverty Action , London , UK
• 7 Faculty of Health , Deakin University , Burwood , Victoria , Australia
• Correspondence to Dr Win Htike; win.htike{at}burnet.edu.au

Objectives To achieve malaria elimination by 2030, the Lao People’s Democratic Republic (PDR) adopted a reactive surveillance and response (RASR) strategy of malaria case notification within 1 day, case investigation and classification within 3 days and foci investigation and response within 7 days. It is important to evaluate the performance and feasibility of RASR implementation in Lao PDR so that the strategy may be optimised and better contribute towards the goal of malaria elimination.

Design A mixed-methods study comprising of secondary data analysis of routinely collected malaria surveillance data, quantitative surveys and qualitative consultations was conducted in 2022.

Setting Primary data collections for quantitative surveys and qualitative consultations were conducted in Huaphan, Khammouane, Luangprabang and Savannakhet Provinces of Lao PDR.

Participants Quantitative surveys were conducted among malaria programme stakeholders and service providers. Qualitative interviews were conducted with malaria programme stakeholders, and focus group discussions with malaria programme stakeholders, service providers and mobile and migrant populations (MMPs).

Outcome measures Outcomes of interests were awareness and acceptability of current RASR activities by different group of participants, implementation, performance and feasibility of RASR activities including enablers and barriers.

Results In Lao PDR, malaria programme stakeholders and service providers were aware of RASR; however, these activities were not well known in MMPs. Respectively, the timeliness of case notification and case investigation was 0.0% and 15.6% in 2018 but increased to 98.0% and 98.6% in 2022. Implementation of RASR was acceptable to the malaria programme stakeholders and service providers, and continued implementation was perceived as feasible. Nevertheless, issues such as low level of community awareness, high level of migration and limitations in health system capacity were identified.

Conclusion Overall, the timeliness of case notification and investigation in Lao PDR was high, and malaria programme stakeholders and service providers had positive opinions on RASR. However, some operational and health system-related barriers were identified, which need to be addressed to improve the performance of RASR in Lao PDR.

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Data availability statement

Data are available upon reasonable request. The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See:  http://creativecommons.org/licenses/by-nc/4.0/ .

https://doi.org/10.1136/bmjopen-2023-083060

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STRENGTHS AND LIMITATIONS OF THIS STUDY

This was a mixed-method study that used diverse data collection methods and included different groups of participants ranging from mobile and migrant populations, frontline malaria service providers to higher level malaria programme stakeholders.

Findings from different methods were triangulated to increase the breadth and depth of understanding of performance and operational feasibility of reactive surveillance and response (RASR) strategies and activities in Lao PDR.

Completeness and effectiveness of RASR activities, essential parameters for measuring the success of the RASR strategy, could not be assessed due to limitations in the secondary dataset.

Future evaluations will benefit from the assessment of these essential parameters and their contribution to effective RASR implementation.

Introduction

Over the last decade, the Lao People’s Democratic Republic (Lao PDR), a country in the Greater Mekong Subregion (GMS), has made a significant reduction in its malaria burden. Between 2010 and 2021, malaria morbidity and mortality in Lao PDR decreased by 83% and 96%, respectively, 1 and malaria is currently only endemic in the Southern Provinces of Lao PDR. Lao PDR has committed to eliminate falciparum malaria by 2025 and all malaria species by 2030. 2

In the elimination programme, all parasitologically confirmed index malaria cases (a malaria index case is a passively detected malaria case that triggers the reactive surveillance and response (RASR) activities) detected by a malaria service provider must be notified in a timely manner, followed by case and focus investigations. This process seeks to reliably determine the source of infection and classify cases and foci to inform an appropriate response. These activities are interconnected and are referred to as case detection and notification, case investigation and classification and foci investigation and response, or herein collectively referred to as RASR. 3 Since 2018, Lao PDR started applying the ‘1-3-7 strategy’ in 17 provinces, a time-bound malaria RASR strategy developed by China in 2012 4 that entails case notification within 1 day, case investigation and classification within 3 days and focus investigation and response activities within 7 days after a malaria case is diagnosed. 5

It is vital to evaluate the performance and feasibility of the implementation of RASR strategies to provide recommendations to improve the surveillance system and ultimately contribute towards achieving national and regional malaria elimination targets. This mixed-methods evaluation study is part of a multicountry assessment of RASR strategies in the GMS. 6 7 It aims to comprehensively review and analyse the RASR strategies that are currently used in Lao PDR with specific objectives, (1) assess the awareness and acceptability of current RASR activities by malaria programme stakeholders, malaria service providers and mobile and migrant populations (MMPs); (2) investigate the implementation and performance of RASR activities in Lao PDR; (3) explore the feasibility of RASR implementation by identifying enablers and barriers and (4) explore how current RASR strategies can be optimised to overcome existing barriers and improve their effectiveness to achieve malaria elimination.

Study design and participants

A mixed-methods study was conducted between September and October 2022, and detailed procedures are outlined in online supplemental material 1 . Briefly, secondary analysis of an aggregated subset of the routinely collected malaria surveillance data from the provinces in malaria elimination phase, quantitative surveys of malaria programme stakeholders (disease control unit leaders and Vector Borne Disease Control Unit staff from the Provincial and District Health Offices) and malaria service providers (health centre and primary healthcare facility staff and village malaria workers (VMWs)) and qualitative consultations such as focus group discussions (FGDs) with malaria programme stakeholders, malaria service providers and MMPs and semistructured interviews with malaria programme stakeholders, was conducted. Study reporting adhered to the Strengthening the Reporting of Observational Studies in Epidemiology and Standards for Reporting Qualitative Research checklists ( online supplemental materials 2A,B ).

Supplemental material

Study setting.

Primary data collections for quantitative surveys and qualitative consultations were conducted in four provinces of Lao PDR—Huaphan (Sopbao district), Khammouane (Boualapha and Thakhek districts), Luangprabang (Phoukhoun district) and Savannakhet (Vilabouli district) provinces ( figure 1 ). These provinces were purposively selected to capture the different stages of elimination across the regions of Lao PDR, such as provinces where all districts (Huaphan and Luanprabang provinces) or most districts (Khammouane province) reported no malaria cases and provinces with several high-burden districts (Savannakhet province) in 2022.

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Study areas in Lao PDR*. *Map generated using QGIS application V.3.22.0 using base maps from the Lao PDR Administrative Boundary Common Operational Database developed by the United Nations Office for the Coordination of Humanitarian Affairs (UNOCHA) downloaded from https://data.laos.opendevelopmentmekong.net/dataset/ .

Data collection, management and analyses

For the purpose of secondary data analysis, the Laos Centre of Malariology, Parasitology and Entomology provided secondary datasets containing aggregated data on malaria testing, treatment and surveillance collected through routine malaria surveillance system and performed by staff from health centres as well as district and provincial disease control teams in all 17 provinces in malaria elimination phase between 01 Jan 2018 and 31 Dec 2022. The raw secondary dataset was stored in Microsoft Excel with separate spreadsheets for malaria testing and treatment, malaria case notification and investigation and foci investigation and responses. The Microsoft Excel spreadsheets were imported to Stata V.17.0 (StataCorp, Texas, USA), where they were merged to form a dataset ( online supplemental material 3 ) and analysed to assess the timeliness of case notification and investigation. Timeliness of foci investigation and response activities could not be assessed due to limitations in the secondary dataset.

Quantitative questionnaires in the Lao language were administered to 28 malaria programme stakeholders (Questionnaire one in online supplemental material 4 ) and 37 malaria service providers (Questionnaire two in online supplemental material 4 ) to explore their awareness and practice of current malaria RASR strategies and feasibility of implementing these strategies in Lao PDR ( online supplemental material 5: additional table 1 ). Participants were recruited purposively based on their working experience, malaria burden of their responsible geographical area, operational feasibility to collect data and the implementation of malaria elimination strategies at the time of survey. The quantitative data were collected using Research Electronic Data Capture (REDCap) and exported to Microsoft Excel files. Open responses were translated to English and then exported into Stata V.17.0 (Stata Corp, Texas, USA), where the survey data was cleaned and descriptively analysed.

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Reactive case detection in Lao PDR as reported by surveyed participants

A subset of surveyed malaria programme stakeholders, malaria service providers and MMPs were recruited purposively for qualitative consultations. Four semistructured interviews with malaria programme stakeholders (male: 3; female: 1), five FGDs with 14 malaria programme stakeholders (male: 11; female: 3) (in groups of 2–4), six FGDs with 24 malaria service providers (male: 11; female: 13) (in groups of 3–5) and four FGDs with 20 MMPs (male: 14; female: 6) (in groups of 3–6) were conducted ( online supplemental material 5: additional table 2 ). Interview and FGD guides ( online supplemental material 4 ) were used to explore the perceptions and practices of current malaria RASR strategies and acceptability and feasibility for successful implementation of these strategies in Lao PDR. Malaria programme stakeholders and malaria service providers were purposively recruited based on their roles and experience implementing malaria RASR strategies in Lao PDR. Study participants at the village level such as VMWs and MMPs were purposively recruited if their villages were in the coverage of the selected primary healthcare facility where RASR strategies have been rolled out. Interviews and FGDs were audio recorded, transcribed verbatim and translated into English. They were then organised, managed and analysed thematically (deductive followed by inductive analysis) 8 in NVivo (Release 1.7.1) by two researchers who immersed and coded data and then discussed themes and subthemes to reach a consensus on the interpretation. 9

Recommendations to improve RASR in Lao PDR

Patient and public involvement

This study used non-identified aggregated secondary data extracted from routinely collected national malaria surveillance system database. As such, patients were not engaged nor involved in this research. Village malaria workers and mobile and migrant populations from respective community were involved in data collection. Refer to the Methods section and online supplemental material 1 (Additional methods) for further details.

Awareness and acceptability of RASR activities

All (100%, 28/28) surveyed malaria programme stakeholders reported that the 1-3-7 strategy was the time-bound RASR strategy adopted by the Laos Centre of Malariology, Parasitology and Entomology. However, only 59.5% (22/37) of malaria service providers recalled the 1-3-7 strategy, and 35.1% (13/37) responded that they were not aware of any time-bound RASR strategy. In addition, 5.4% (2/37) of malaria service providers responded that there was another time-bound RASR strategy adopted by the malaria programme, though they were unable to recall what the time frames were.

Interviewees and FGD participants reported that the 1-3-7 strategy was well accepted by malaria programme stakeholders and service providers. Moreover, participants claimed that the 1-3-7 strategy was appropriate and effective because it provided a timely response to interrupt the onward transmission of malaria in their assigned geographical areas. Participants also believed that the 1-3-7 strategy was effective for malaria elimination given that the number of malaria cases had decreased in areas implementing the 1-3-7 RASR strategy, and no new malaria cases were identified for many years in those areas.

… if we follow the 1-3-7 strategy, we can eliminate malaria on time as planned… (A malaria programme stakeholder and FGD participant)

At the grass-roots level, MMPs were not aware of RASR activities such as malaria case notification, case investigation, focus investigation and response as there were no malaria cases in their villages or worksites, although some of them mentioned in FGD that routine malaria prevention, control and diagnosis services such as distribution of mosquito nets and blood testing for malaria were available in their community.

We used to hear that there were some malaria cases in our area before, but we do not hear about it (malaria) anymore… we don’t know what kind of activities are carried out once a malaria patient has been detected. (An MMP and FGD participant)

Implementation and performance of RASR activities

In surveys, malaria programme stakeholders commonly reported electronic reporting system using mobile phones or mobile tablets (89.3%, 25/28) and paper-based reporting (85.7%, 24/28) as methods for reporting malaria cases. Additionally, the majority of malaria service providers reported that they notified malaria cases to the malaria programme stakeholders by direct phone calling (75.7%, 28/37).

After a malaria positive case had been notified, case investigation was mostly led or supervised by the district malaria control unit or district health office (71.4%, 20/28). About half of the surveyed malaria service providers (48.6%, 18/37) responded that they were involved in every case investigation executed within their responsible areas. Among those who were never involved in case investigation before (37.8%, 14/37), almost all of them (92.9%, 13/14) reported that they were willing to be involved in case investigation in the future ( online supplemental material 5: additional table 3 ).

The majority of surveyed malaria programme stakeholders and malaria service providers reported that during a case investigation, the investigator(s) visited the index case (83.1%, 54/65), checked malaria preventive measures used by the index case (84.6%, 55/65), educated the index case on malaria prevention (84.6%, 55/65) and collected travel history of the index case (83.1%, 54/65). In addition, 58.5% (38/65) of the surveyed malaria programme stakeholders and malaria service providers mentioned that the location of the index case was mapped during a case investigation by taking the Global Positioning System coordinates ( online supplemental material 5: additional table 4 ).

During qualitative consultations, malaria programme stakeholders mentioned that after investigating and classifying malaria cases according to the National Guidelines, the responsible team which was comprised of district disease control team and designated health facility staff conducted reactive case detection (RACD) as part of the foci investigation and responses. In surveys, malaria programme stakeholders and service providers responded that RACD was triggered either by local cases only (40.0%, 26/65) or by both local and imported cases (46.2%, 30/65). The majority of survey participants (86.2%, 56/65) mentioned that household members of the index case were screened during RACD. All malaria programme stakeholders (100%, 28/28) stated that neighbours of the index case need to be screened during RACD; however, only 62.2% (23/37) of the malaria service providers mentioned that they did so ( table 1 ).

Surveyed participants reported that there were no standardised procedures for conducting RACD. Almost all malaria programme stakeholders (92.9%, 26/28) reported that all household members should be screened during RACD whether they had a fever or not. However, about half (51.4%, 19/37) of the malaria service providers reported that they screened all household members regardless of fever, and 35.1% (13/37) mentioned that only the febrile cases were screened. The majority of malaria programme stakeholders (71.4%, 20/28) reported that all neighbours of the index case should be screened regardless of fever, and 28.6% (8/28) mentioned that only the febrile cases should be screened. About half of the surveyed malaria service providers (48.6%, 18/37) reported that all neighbours were screened during RACD regardless of fever, and approximately one-quarter (24.3%, 9/37) mentioned that only febrile cases were screened. Survey respondents also reported variations in the median number of neighbours (13, IQR: 5, 50), households (10, IQR: 5, 24) and geographical parameter (radius in metres; 125, IQR: 50, 500) around the index case screened during an RACD ( table 1 ).

During FGD, malaria service providers mentioned that they did not understand the process of RACD because there were no malaria cases in their geographical areas, or they were not aware of any specific guidelines or instructions for RACD. Malaria programme stakeholders also highlighted during interviews that there were human resource and financial challenges in doing RACD as part of the RASR strategy.

Apart from RACD, other commonly conducted focus response activities as reported in surveys included awareness raising among community members on malaria transmission, malaria prevention and vector control measures if needed, entomological surveillance, and spot checks for mosquito breeding places if proper entomological surveillance was not feasible ( online supplemental material 5: additional table 5 ).

Timeliness of RASR activities in Lao PDR

Secondary analysis of malaria data from the districts in the elimination phase revealed that the total number of malaria cases per year ranged between 77 (in 2019) and 257 (in 2018). Among 17 reporting units, Khammouan province consistently held the largest number of malaria cases every year, making up 54%–88% of total cases except for the year 2022 ( online supplemental material 5: additional table 6 ).

In 2018, none of the included provinces achieved timely case notification within 1 day. Of the total cases, only 1.3% in 2019 and 0.5% in 2020 achieved timely case notification within 1 day. However, from 2021 onwards, >95% of cases were reported in 1 day, with eight out of 10 provinces achieving 100% timeliness in case notification in 2022. Overall, timely case investigation significantly increased from 15.6% in 2018 to 74.0% (57/77) in 2019, 82.1% (170/207) in 2020 and increasing further to 97.2% (105/108) in 2021 and 98.6% (145/147) in 2022. In 2022, 100% timeliness in case investigation was noted for eight out of 10 provinces ( figure 2 ; online supplemental material 5: additional table 6 ).

Overall timeliness of case notification and investigation in malaria elimination provinces of Lao PDR during 2018–2022 (source: secondary data analysis).

Enablers of RASR activities in Lao PDR

An enabler of RASR activities in Lao PDR was the strong perception of malaria programme stakeholders that the 1-3-7 strategy was an effective approach to achieve malaria elimination if carried out in a timely manner. They also reported that the 1-3-7 strategy was appropriate for their areas, and they already introduced and advocated its use for malaria elimination across all the districts in their provinces.

Malaria service providers reported in FGDs and interviews that the 1-3-7 strategy was feasible to implement in their geographical areas because they believed that the health centre staff and VMWs were knowledgeable about their local context and could approach target populations well. Malaria programme stakeholders also reported that health staff and VMWs could participate in different RASR activities such as case notification, investigation and response. Furthermore, malaria service providers reported that although many community members did not understand the objective and goals of such activities, there was good community participation in RASR activities because they believed in service providers.

Almost all the health staff are from the local community so that they are well familiar with location and context … they can participate in different activities like giving health education, notifying, reporting and investigating malaria cases, and assisting response activities. (Interview with a malaria programme stakeholder)

Barriers for RASR activities in Lao PDR

Survey results showed that about half of the participants believed there were no barriers in conducting case notification within 1 day (44.6%, 29/65), case investigation within 3 days (50.8%, 33/65) or foci investigation and response activities within 7 days (40.0%, 26/65) ( online supplemental material 5: additional table 7 ). However, some operational and health system-related barriers were identified during interviews and FGD.

Operational barriers for RASR activities in Lao PDR

Having many MMPs in an area was identified as an operational barrier for the successful implementation of RASR activities in Lao PDR because of their mobility patterns and the nature of their workplaces. MMPs in some villages and districts were travelling from one place to another in a relatively short period of time, which made the completion of all steps of RASR activities difficult for malaria service providers to achieve. Malaria service providers perceived that the completeness of RASR activities was undermined by MMPs working in remote rubber plantation sites, which are not easily accessible. Further, owners of rubber plantation sites did not cooperate well with the health sector in performing RASR activities among MMPs. Malaria service providers suggested that a strategy such as cooperation with relevant authorities from labour offices and business owners should be developed to improve access to MMPs and strengthen RASR strategies.

Data collection (for RASR) among this group of population (MMP) is challenging because almost every migrant comes and sells the goods in the village and district for a short period like one or two days. And then they move on to other places. (A malaria programme stakeholder and FGD participant)

Another operational barrier for the successful implementation of RASR activities in Lao PDR was inaccessibility to at-risk populations in the community. Malaria programme stakeholders and malaria service providers reported that some villages were far away from the health centres and were difficult to access, preventing timely implementation of RASR activities, especially in the rainy season. Additionally, it was reported that some villages at risk of malaria did not have mobile phone network or internet access, resulting in delays to every step of RASR activities. Malaria programme stakeholders and malaria service providers reported that there were telecommunication barriers to conduct case notification within 1 day (36.9%, 24/65) ( online supplemental material 5: additional table 8 ). Consistent with the quantitative finding, malaria programme stakeholders also reported during semistructured interviews and FGDs that the timing of RASR activities was negatively impacted by transportation and telecommunication difficulties. Suggested approaches to improve timely notification of malaria cases and subsequent RASR activities included the provision of mobile top-up cards and transportation to hospitals and health centres in remote areas.

RASR activities cannot be carried out in some areas according to the 1-3-7. Especially in remote and hard-to-reach areas where the road is cut off and there is no phone signal. It is the main obstacle for implementation (of 1-3-7 strategy). (A malaria programme stakeholder and FGD participant)

Health system-related barriers for RASR activities in Lao PDR

Both the malaria programme stakeholders and the malaria service providers reported challenges related to human resources in conducting RASR activities. They reported that there were not enough staff in the health facilities, that most of the existing staff were overburdened with many assignments and tasks and that they were untrained for RASR activities. Malaria service providers also reported in the FGD that they had to involve VMWs in performing RASR activities.

At the health centre level, the staff is not enough. Existing staff have to do many different tasks, so we have to use volunteer staff. Using volunteer staff is not sustainable and it needs to be changed for good. (A malaria service provider and FGD participant)

During semistructured interviews and FGDs, the participants identified a skilful and cooperative team effort as a necessity for the successful implementation of RASR strategies. Malaria programme stakeholders and malaria service providers suggested that regular training of health centre staff and VMWs was required to improve their knowledge and skills in RASR strategies and activities. Moreover, all stakeholders reported that community involvement was important in conducting RASR activities as the effort from health workers alone was not sufficient.

Another barrier for successful implementation of RASR activities was lack of available funds for RASR at the district health offices, which could only be applied for after a positive case was reported. The process of applying for, approving and withdrawing the necessary budget for RASR activities often took too long and hindered the completion of RASR activities as per the 1-3-7 time schedule. To avoid such delays, malaria service providers used readily available budgets reserved for other administrative purposes in the first place and reimbursed from RASR budget after completing the response activities. However, delays in RASR activities were inevitable when district health offices had no other reserved budget. Malaria programme stakeholders suggested that a reserved fund for RASR activities should be readily available, and budget approval and disbursement processes should be completed in a timely manner to avoid delays in the implementation of RASR activities.

Overall, the 1-3-7 strategy is the policy-endorsed RASR strategy in Lao PDR and is well accepted by malaria programme stakeholders and malaria service providers. The implementation of RASR strategy in Lao PDR was satisfactory after 2020 in terms of timeliness of case notification and investigation. However, this study also highlighted some key issues and ways for improving the effectiveness of RASR strategy and accelerating Lao PDR’s progress towards malaria elimination.

Even though the RASR strategy was first launched in Lao PDR in 2018, its attributable indicators were only added to the national reporting system the following year. Guidelines and training followed afterwards due to programmatic complexity and financial constraints. As such, complete guidelines and training tools were not fully disseminated until 2020. In 2022, 17 out of 18 provinces in Lao PDR were in the malaria elimination phase except for Attapeu province which was still in the burden reduction phase. Timeliness of case notification and investigation in malaria elimination districts of these 17 provinces improved drastically in 2021 and 2022 compared with earlier years. Such drastic improvement in the timeliness of RASR activities could be attributable to the rolling out of the RASR guidelines and trainings to health facility staff at different levels in 2020 and 2021, programme planning exercises which applied a bottom-up approach considering the resource gaps at different levels of health system, and full integration of RASR data into District Health Information Software 2 (DHIS-2) which is the routine health management and information system in Lao PDR. To maintain the impressive achievement of timely case notification and investigation, refresher trainings for health facility staff at different levels should be continued.

Malaria programme stakeholders and service providers had a common understanding of investigating and classifying malaria cases; however, variations were noted in steps and parameters for subsequent RACD activities. Like in other GMS countries, 6 even though malaria service providers in Lao PDR screened the household members of the index case and the neighbouring households, there was no specific demarcation for the number of neighbours, households or a geographical radius to be screened during RACD. It is also important to carefully determine which population to test during RACD as this should be based on the case and where the case caught malaria. For example, in Cambodia, cotravellers or coexposed persons were also screened during RACD. 10 11 In addition to specified and detailed geospatial guidelines for RACD, capacity building and training for RACD should also be carried out at different levels so that all the malaria service providers have a common understanding of the RACD process, which is important for detecting afebrile malaria infections and interrupting the onward transmission of malaria in the community. 12

Successful implementation of RASR activities requires community engagement and it is important that the community believes in and commits to malaria elimination strategies. 13 While awareness of RASR strategies and activities was high among malaria programme stakeholders and malaria service providers, the community was not fully aware of RASR activities nor the goal and objectives of these activities. Awareness raising through mass media and campaigns should be considered to improve the community’s knowledge of malaria RASR as it plays a crucial role in sustainability of a malaria elimination programme. 14 It is also crucial to engage the community in planning, implementing and evaluating the different steps of RASR strategies to ensure that the strategies and activities meet the community’s behaviour and health needs. 15 In addition, policy makers and programme implementers should take human behaviour and sociocultural context into account for successful malaria control and elimination at the community level, 16 and it is important to understand the community’s perception of malaria since it influences and shapes their attitude and behaviour towards malaria prevention, control and elimination efforts. 17

As in other GMS countries, 6 18 the malaria elimination programme in Lao PDR is facing challenges posed by MMPs. MMPs are highly mobile due to the nature of their work and have difficulties in accessing malaria and other healthcare services from formal healthcare providers. MMPs are considered vulnerable and at a high risk of malaria in the GMS due to their workplace environment and shelters which are usually constructed poorly, and the requirement to work or sleep outdoors resulting in increased exposure to malaria vectors. 18 Frequent migration of MMPs to pursue temporary employment also precludes adequate access to malaria prevention and treatment services. 19 Due to MMPs’ frequent migration from one place to another compounded by difficult road conditions and remoteness, health service providers reported that it was challenging to do RACD and other necessary response measures within the recommended timeframe (ie, within 7 days of a case diagnosis in Lao PDR). Consequently, onward transmission might not be interrupted among MMPs, and they could reintroduce imported cases into malaria-free areas. 20–25 Hence, it is critical to formulate MMP-orientated RASR strategies and intervention packages. Currently, the Laos Centre of Malariology, Parasitology and Entomology is trying to implement targeted approaches for MMPs such as distributing long-lasting insecticidal nets (LLINs) and using peer educators in order to interrupt the residual transmission among them and achieve malaria elimination in Lao PDR. In addition, using innovative and attractive approaches to increase MMPs’ awareness on malaria through popular social media platforms (eg, TikTok) should also be considered.

Another challenge reported by participants was telecommunication difficulty in remote areas, which was perceived to pose a threat to the effective implementation of RASR strategies. In surveys with malaria service providers, it was reported that malaria cases were mainly notified through direct phone calling. Timeliness of case notification could be negatively affected by difficult telecommunication, which in turn could cause delays in subsequent RASR activities such as case investigation, focus investigation and response activities. Providing travel incentive and mobile top-up cards to malaria service providers from areas with poor internet or mobile connections could be a practical solution so that they could commute to the nearest place with accessible telecommunication service. Task shifting some of the RASR activities to VMWs could also be a feasible solution to prevent delays in implementation of RASR activities due to difficulties in transportation and telecommunication.

Lao PDR is facing challenges in its health system for the successful implementation of RASR strategy such as prolonged cash flow mechanism and lack of human resources. Many malaria programme stakeholders reported a lack of reserved funds at the district level as well as lengthy and complicated funding modalities which might lead to delayed implementation of RASR activities. Funding mechanisms and cycles were considered important for the successful and timely implementation of malaria elimination activities including RASR, and it is important to harmonise health system funding and the national malaria elimination action plan. 26 Limitations in human resources for RASR activities are a common challenge for malaria elimination programmes in the GMS, 6 7 26 and may contribute to an overburdened workforce assigned various responsibilities beyond their capacity. 7 Task shifting of some RASR activities such as case investigation and classification and preliminary focus investigation to VMWs could be a reasonable solution for the sustainability of VMWs as well as the successful implementation of RASR activities. While it is important to find solutions to gap-fill human resource problems, the performance of existing health staff could also be significantly improved through regular and refresher trainings that address their operational challenges in the field 17 and by ensuring that job aids and SOPs are readily available for them.

Strengths and limitations of the study

This was the first mixed-method study to comprehensively evaluate the performance and operational feasibility of RASR strategies and activities in Lao PDR. The study has used diverse data collection methods and included participants from different levels ranging from MMPs and frontline malaria service providers to higher-level malaria programme stakeholders. Moreover, findings from different methods were triangulated to increase the breadth and depth of understanding of the study findings.

Completeness and effectiveness, essential parameters for measuring the success of RASR strategy could not be assessed due to limitations in the secondary dataset, which provided no more than the provincial-level aggregated data with a limited number of variables ( online supplemental material 3 ). Due to this limitation, completeness of each step of RASR strategy and effectiveness of RACD could not be calculated ( online supplemental material 1: section 3 ).

Recommendations and conclusion

Overall, the implementation of RASR strategy for malaria elimination is on the right track in Lao PDR. The timeliness of case notification and investigation was found to be satisfactory after 3 years of implementation, and the opinions and perception of malaria programme stakeholders and malaria service providers towards RASR strategies were encouraging. However, this study highlighted the important barriers to effective implementation of RASR strategies in Lao PDR. To further strengthen RASR strategies in accelerating towards malaria elimination in Lao PDR, this study provides a set of recommendations in table 2 . Optimisation of RASR strategy by following these recommendations will accelerate malaria elimination in Lao PDR, which in turn will contribute to the malaria elimination in the GMS by 2030.

Ethics statements

Patient consent for publication.

Not applicable.

Ethics approval

The study protocol was approved by the Alfred Ethics Committee (393/21) and the National Ethics Committee for Health Research of Lao PDR (06/NECHR). All methods and procedures were performed in accordance with the relevant guidelines and regulations set by those institutions. Written informed consent was obtained from all study participants. Study participants were compensated for their time and travel cost. Amount of compensation was 100 000 to 150 000 Lao Kip (about 4.5–7 US$) depending on their travel distance.

Acknowledgments

We would like to thank malaria programme stakeholders, malaria service providers, local communities and village malaria workers for their participation in the research; The Centre of Malariology, Parasitology and Entomology, provincial, district and health offices of Huaphan, Khammouane, Luangprabang and Savannakhet provinces, and local health authorities from Lao PDR for the local advocacy, coordination and preliminary planning of field work; Burnet Institute staff Chad Hughes, Julie Tartaggia and Phone Myint Win for technical, coordination and management support; Health Poverty Action staff Wang Bangyuan, Josien Van Der Kooij, Bangone Santavasy and Silayan Bertomeu for their coordination and management support.

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X @freyafowkes

WH and WHO contributed equally.

Contributors FJIF, PAA, JCC, WHO and WH designed the study and prepared the study protocol with inputs from BK, PV, VB, KC and TL. TL, SV, MCO, EPH, AKZ, KMT, GNH and KMK supervised and performed data collection. NAT undertook secondary data analysis of national malaria data and quantitative data analysis of surveys with malaria programme stakeholders and malaria service providers under the supervision of PAA and WHO. TL and WH analysed qualitative data collected from semistructured interviews and FGDs. WH prepared the first draft of the manuscript which was reviewed and revised by WHO, EK and KOF under the guidance of FJIF. All authors reviewed and contributed to the final manuscript. All authors read and approved the final manuscript. FJIF accepts full responsibility for the finished work and/or the conduct of the study, had access to the data and controlled the decision to publish.

Funding This study was funded by an international funding organisation (Grant Number: QSE-M-UNOPS-BI-20864-007-61) to all authors and the National Health and Medical Research Council of Australia (Leadership Fellowship (2017485) and Centre for Research Excellence (1134989)) awarded to FJIF. The Burnet Institute is funded by a Victorian State Government Operational Infrastructure Support grant. Investigators from the Centre of Malariology, Parasitology and Entomology are government staff, and their salaries and infrastructure are contributed by the Laos Ministry of Health. The funders have no input on the design, collection, analysis, interpretation and publication of the study results.

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Competing interests None declared.

Patient and public involvement Patients and/or the public were involved in the design, conduct, reporting or dissemination plans of this research. Refer to the Methods section for further details.

Provenance and peer review Not commissioned; externally peer reviewed.

Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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Malaria diagnosis: a brief review

Affiliation.

• 1 Critical Care Research Unit, Department of Clinical Tropical Medicine, Mahidol University, Bangkok, Thailand. [email protected]
• PMID: 19488414
• PMCID: PMC2688806
• DOI: 10.3347/kjp.2009.47.2.93

Malaria is a major cause of death in tropical and sub-tropical countries, killing each year over 1 million people globally; 90% of fatalities occur in African children. Although effective ways to manage malaria now exist, the number of malaria cases is still increasing, due to several factors. In this emergency situation, prompt and effective diagnostic methods are essential for the management and control of malaria. Traditional methods for diagnosing malaria remain problematic; therefore, new technologies have been developed and introduced to overcome the limitations. This review details the currently available diagnostic methods for malaria.

Keywords: Plasmodium; diagnosis; malaria; method.

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Conflict of interest statement

The authors declare no conflict of interest.

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Exploring Integration of Multimodal Deep Learning Approaches for Enhanced Alzheimer's Disease Diagnosis: A Review of Recent Literature

• Review Article
• Published: 02 September 2024
• Volume 5 , article number  852 , ( 2024 )

Cite this article

• Sonali Deshpande 1 &
• Nilima Kulkarni 1  

Alzheimer's disease (AD), is the most common form of dementia that affects the nervous system. In the past few years, non-invasive early AD diagnosis has become more popular as a way to improve patient care and treatment results. Imaging methods, electroencephalogram (EEG) tests, and sound evaluations are some of the new ways that researchers have looked into. This review covers 60 papers published from 2020. They are compared in terms of how they use basic deep learning models such as CNN, LSTM, Alex Net, Inception Net, VGG19, and ResNet to identify AD. But not many studies use more than one method together, like image and EEG, EEG and sounds, or images and sounds. The information from the Scopus database makes it easy to look at the newest information and work. This means that using more than one method to find AD isn't getting as much attention. Our review says that combining the best parts of each method in a mixed way could make Alzheimer's research much more useful and lead to better ways to diagnose. The paper talks about problems and opportunities in the field right now as well as possible study topics and issues for the future.

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Acknowledgements

The authors acknowledged the MIT Art, Design and Technology University, Pune, India for supporting the research work by providing the facilities.

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Sonali Deshpande & Nilima Kulkarni

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Deshpande, S., Kulkarni, N. Exploring Integration of Multimodal Deep Learning Approaches for Enhanced Alzheimer's Disease Diagnosis: A Review of Recent Literature. SN COMPUT. SCI. 5 , 852 (2024). https://doi.org/10.1007/s42979-024-03084-w

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Hyperuricemia and its related diseases: mechanisms and advances in therapy

1 Sports Medicine Center, The First Affiliated Hospital of Shantou University Medical College, Shantou, 515041 China

2 Institute of Sports Medicine, Shantou University Medical College, Shantou, 515041 China

3 Centre for Orthopaedic Research, Medical School, The University of Western Australia, Nedlands, WA 6009 Australia

4 Department of Orthopaedics, Shanghai Sixth People’s Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, 200233 China

Changqing Zhang

Zhigang zhong.

Hyperuricemia, characterized by elevated levels of serum uric acid (SUA), is linked to a spectrum of commodities such as gout, cardiovascular diseases, renal disorders, metabolic syndrome, and diabetes, etc. Significantly impairing the quality of life for those affected, the prevalence of hyperuricemia is an upward trend globally, especially in most developed countries. UA possesses a multifaceted role, such as antioxidant, pro-oxidative, pro-inflammatory, nitric oxide modulating, anti-aging, and immune effects, which are significant in both physiological and pathological contexts. The equilibrium of circulating urate levels hinges on the interplay between production and excretion, a delicate balance orchestrated by urate transporter functions across various epithelial tissues and cell types. While existing research has identified hyperuricemia involvement in numerous biological processes and signaling pathways, the precise mechanisms connecting elevated UA levels to disease etiology remain to be fully elucidated. In addition, the influence of genetic susceptibilities and environmental determinants on hyperuricemia calls for a detailed and nuanced examination. This review compiles data from global epidemiological studies and clinical practices, exploring the physiological processes and the genetic foundations of urate transporters in depth. Furthermore, we uncover the complex mechanisms by which the UA induced inflammation influences metabolic processes in individuals with hyperuricemia and the association with its relative disease, offering a foundation for innovative therapeutic approaches and advanced pharmacological strategies.

Introduction

Hyperuricemia is a metabolic disorder marked by elevated serum uric acid concentrations in both extracellular fluids and tissues, coupled with impaired uric acid excretion. 1 The definition of hyperuricemia is SUA level ≥ 7.0 mg/dl (416.0 μmol/L) in males or ≥ 6.0 mg/dl (357.0 μmol/L) in females. 2 Hyperuricemia is associated with various risk factors, including a high-purine diet, alcohol consumption, medication usage, hypertension, hypothyroidism, and obesity. Additionally, social factors such as higher socioeconomic status, as well as a history of smoking and alcohol use, further contribute to the heightened risk of developing this condition. 1 , 3 , 4 UA plays a double-edged sword role in humans. 5 Uric acid possesses antioxidant capabilities that combat free radicals and reactive oxygen species, thus preventing oxidative stress. 6 – 8 The antioxidant effect of uric acid can be manifested in the inhibition of cell death to protect nerves as well as profile support of NO-mediated vasodilation. 9 However, uric acid will be transformed into a pro-oxidant and pro-inflammatory molecule that exacerbates oxidative stress when the UA levels are increased. 10 – 12 UA, mediates the innate immune response, which can release inflammatory mediators and activate the renin-angiotensin system, 13 inflammatory responses, oxidative stress, vascular endothelial dysfunction and insulin resistance. 14 – 16 Mendelian randomization studies have demonstrated no causal relationship between elevated uric acid levels and the risks of diabetes, coronary heart disease, ischemic stroke, heart failure, body mass index, bone mineral density, coronary artery disease, blood pressure, metabolic syndrome, blood glucose levels, triglyceride levels, diabetes mellitus, serum creatinine levels, glomerular filtration rate, and Parkinson’s disease. 17 – 21 The only phenotypes that were causally associated with HU were gout and kidney disease. 22 However, epidemiological and clinical studies have linked hyperuricemia to the development of various conditions, including chronic kidney disease, fatty liver, metabolic syndrome, hypertension, insulin resistance, obesity, type 2 diabetes, and cardiovascular and cerebrovascular disorders. 1 , 23 – 25 In this article, we review the complex physiological roles and metabolism of uric acid and the interconnections of mechanisms between hyperuricemia and potential diseases. Furthermore, we summarize the novel therapeutic interventions for hyperuricemia by examining its common comorbidities, underlying mechanisms, phenotypes, and pathogenesis.

The timescale and prevalence of hyperuricemia

Among history, Podagra first developed and identified by Hippocrates, which called “unwalkable illness” in 400 BC. with the definition podagra as a style called “arthritis of the rich.” Over 2000 years ago, Colchicine, initially used as a purgative in ancient Greece, which was later recognized by Alexander of Tralles in the sixth century AD for its specific therapeutic effects on arthritis. 26 By 1200, gout was dubbed the ‘disease of kings’ due to its association with a luxurious lifestyle. In 1679, Antonie van Leeuwenhoek, a pioneer in microbiology, first observed crystals from tophi in gout patients. The chemical composition of uric acid was identified by a Swedish chemist in 1797, and by 1940, the understanding of uric acid metabolism, including its excretion and overproduction was established. 27 – 30 The role of genetic factors in hyperuricemia prevalence was discovered in the 1960s. In 1963, the introduction of Allopurinol, an inhibitor of xanthine oxidase, marked a significant advancement in treating hyperuricemia. More recently, in 2010, uricase enzymes like Pegloticase and Rasburicase were approved for the management of persistent arthritis in patients with comorbidities and joint deformities. 31 – 33 Currently, the emerging drugs and some advanced treatments such as uricosuric compounds, antidyslipidemic drugs or gut microbiota, can reduce the concentration of serum uric acid to address resistant hyperuricemia (Fig. ​ (Fig.1 1 ).

The timescale and historical development of hyperuricemia (depicted in light red) and hyperuricemia treatment (depicted in dark red) from 1944 to June 2024, along with the volume of published literature, have been analyzed using data extracted from PubMed. The search criteria included “hyperuricemia*“ in conjunction with terms such as “history”, “medicine”, “treatment”, “therapy”, “drug”, “mechanism”, “genetic”, and “uric acid”

Hyperuricemia is a globally prevalent condition, particularly in high- and middle-income countries. Its prevalence varies significantly due to factors such as geographic location, regional differences, ethnicity, dietary habits, and economic conditions. Recent trends indicate an increase in the prevalence of hyperuricemia. 2 , 3 The global prevalence rate has been reported to be ranging from 2.6% to 36% in different populations. 34 The U.S. National Health and Nutrition Examination Survey (NHANES) indicates that approximately 21% of adults, or 43 million individuals, have been diagnosed with hyperuricemia. 35 Comparative prevalence rates are as follows: 16.6% in Australia, 36 48% in Finland with a gender-specific breakdown of 60% in males and 31% in females, 37 17.0% in New Zealand with 27.8% in males and 8.8% in females, 38 24.5% in Ireland with 25.0% in males and 24.1% in females, 39 9.9% in Croatia, 40 16.8% in Russia, 41 12.1% in Turkey with 19.0% in male and 5.8% in female, 42 21.2% in Qatar. 43 Likewise, among developing countries, the Korea NHANES reported that the prevalence of hyperuricemia in Korea was 11.4% with 17.0% in male and 5.9% in female. 44 In addition, it is 20.6% in Mexico, 45 17.2% in Niger with 25.0% in male and 13.7% in female, 46 71.6% in French Polynesia, 47 9.9% in Croatia, 40 44.6% in India, 48 28.1% in Jordan, 49 31.8% in sub-Saharan African, 50 10.6% in Thailand with 18.4% in male and 7.8% in female, 51 8.4% in Saudi Arabia 52 and approximately 9.3% in Bangladesh. 53 (Table ​ (Table1) 1 ) As expected, the prevalence of hyperuricemia found in our study is higher in most developed countries. Interestingly, the prevalence of hyperuricemia is higher in coastal areas and countries than in landlocked countries, especially for countries surrounded by sea and in developing. China, with its large population, exhibits significant demographic diversity and regional differences. The prevalence of hyperuricemia was 6.4% in Chinese adults according to a study covering 13 provinces. 2 Geographically, the prevalence of hyperuricemia is highest in southern China (9.1%) and lowest in northern China (3.2%). The majority of affected individuals (71.0%) reside in urban areas, with a substantial proportion (44.7%) living in coastal cities. The prevalence is notably higher in urban regions (8.0%) compared to rural areas (5.0%). By 2014, the overall prevalence of hyperuricemia in mainland China had reached 13.3%, 54 and this gradually increased to 17.7% in 2017. The prevalence was higher in the elderly population, and the rate was higher in male (23.5%) than in female (11.7%). 55

Diagnostic criteria and prevalence for hyperuricemia in each country/area

/, the country without an exact criteria

Physiological role of uric acid

Uric acid is the final product of the catabolism of purine nucleotides. UA is a weak diprotic acid with one dis-sociable H + at physiologic pH values. The concentrations of UA range from 3.5 to 7.2 mg/dL (210–430 μmol/L) in males and 2.6–6.0 mg/dL (155–360 μmol/L) in premenopausal females. 2 , 35 In addition to its role as a byproduct of purine metabolism, uric acid is recognized for its multifaceted effects, which include antioxidant, pro-oxidant, pro-inflammatory, nitric oxide regulation, immune system interactions, and anti-aging properties. 7 , 56

Antioxidant and Pro-oxidant

Uric acid is a natural byproduct of purine metabolism, arising from the enzymatic degradation of hypoxanthine to xanthine, which is subsequently converted by xanthine oxidase. 57 In the process in which uric acid is produced, ROS, particularly superoxide anions and hydrogen peroxide (H 2 O 2 ), are generated as byproducts. 58 – 61 Uric acid functions as a powerful antioxidant, effectively neutralizing singlet oxygen molecules, oxygen radicals, and peroxynitrite (ONOO-) molecules, due to its ability to provide electrons and act as a powerful reducing agent. 27 – 29 , 62 – 65 It can easily provide a hydrogen atom to free radicals, thereby stabilizing them and preventing further oxidative damage. 66 Therefore, uric acid has remarkable antioxidant properties that effectively combat oxidative stress induced by free radicals and reactive oxygen species (ROS). 7 Free radicals are highly reactive entities that can cause oxidative stress and cellular damage and contribute to the development of various diseases. 67 Nevertheless, uric acid has a highly reducing structure that effectively neutralizes free radicals and mitigates their harmful effects. Additionally, uric acid acts as an inhibitor of the oxidative chain reaction through a dual mechanism. 68 , 69 It captures and neutralizes free radicals, forming stable intermediates and thereby impeding the transmission of the oxidative reaction. 66 Furthermore, the complex formed by uric acid and free iron ions acts as a chelating agent, effectively inhibiting the formation of free radicals from iron ions and enhancing the antioxidant effect. 67 Uric acid regulates the inflammatory response by inhibiting the production of inflammatory mediators, which significantly reduces the formation of free radicals. 57 One of the most interesting aspects of the antioxidant function of uric acid is its potential role in neuroprotection. 60 – 62 Uric acid and purines, including adenosine and adenosine triphosphate, have been implicated in regulating central nervous system functions such as convulsive threshold, memory, cognition, sleep, activity, appetite, mood, social interaction, drive, impulsivity, and intelligence. 70 – 72 Some studies have found that patients with neurodegenerative diseases, like Parkinson’s disease, Alzheimer’s disease, and amyotrophic lateral sclerosis (ALS), tend to have lower serum uric acid levels, suggesting a potential neuroprotective effect of uric acid. 73 Patients with major depression and anxiety disorders had lower plasma uric acid levels and increased UA levels after treatment, further suggesting that UA may have a neuroprotective effect. 70 The antioxidant properties of UA and its ability to inhibit oxidative stress may attenuate inflammatory damage to the nervous system and contribute to the maintenance of neuron number and function by inhibiting programmed apoptosis of neuronal cells, which protects against excessive neuronal cell damage. The capacity of uric acid to neutralize reactive oxygen species (ROS) and shield neurons from oxidative damage may underlie its observed neuroprotective effects. Furthermore, the antioxidant properties of uric acid have significant implications for cardiovascular health. 66 The ability of uric acid to scavenge ROS and reduce oxidative stress may have protective effects on the cardiovascular system. Studies illustrated that uric acid may indirectly support NO-mediated vasodilation by preventing nitric oxide degradation by superoxide radicals. This finding implies that uric acid may play a role in maintaining vascular health and regulating blood pressure. 74 The antioxidant function of serum uric acid reflects the multifaceted and complex nature of its physiological role. The ability of uric acid to neutralize free radicals and protect against oxidative stress has implications for all aspects of health. 67 , 75 Interestingly, a level of uric acid that is either too high or too low disrupts the delicate balance of oxidative stress regulation and may lead to excessive oxidative damage or impaired antioxidant defense. At higher intracellular concentrations, uric acid can function as a pro-oxidant molecule. 76 Studies have shown that within various cell types, including vascular smooth muscle cells, endothelial cells, adipocytes, hepatocytes, pancreatic islet cells, and renal tubular cells, uric acid can activate NADPH oxidase, a crucial enzyme involved in the generation of reactive oxygen species. 57 , 76 Moreover, in certain cell types, NADPH oxidase may translocate to the mitochondria, further exacerbating oxidative stress. 77 , 78 The effects of soluble urate on mononuclear cells are multifaceted. Some studies suggest that priming peripheral blood mononuclear cells (PBMCs) with urate enhances the release of interleukin-1β (IL-1β) in response to lipopolysaccharide (LPS), indicating a potential pro-inflammatory effect. 79 While it was found no significant effects of urate on IL-1β release, superoxide dismutase 2 (SOD2) gene transcription, or the total antioxidant capacity of the cell. 80

Pro-inflammatory

Uric acid acts as a danger signal, being naturally released by necrotic cells and subsequently initiating adaptive immune responses. Studies have indicated that uric acid crystals can engage with Toll-like receptors (TLRs), which are membrane-bound receptors integral to innate immunity, thereby inducing inflammation. 10 , 11 , 81 , 82 Specifically, TLR-2, TLR-4, and the myeloid differentiation primary response protein 88 (MyD88) are crucial to the inflammatory reaction of macrophages to uric acid crystals. These crystals can directly interact with these receptors, initiating signal transduction pathways that ultimately activate NF-κB. 83 – 87 NF-κB is a transcription factor responsible for improving the transcription of various inflammation-associated proteins, including pro-interleukin-1 (pro-IL-1), when secreted in the extracellular space. 88 In recent years, studies have revealed that UA activates the TLR4-NLRP3 inflammatory complex, which is a multi-protein complex that plays a pivotal role in initiating the innate immune response to various danger signals, including MSU crystals. Upon recognition of MSU crystals, the NLRP3 inflammasome is activated, leading to the cleavage of pro-inflammatory cytokines, specifically interleukin-1β (IL-1β) and interleukin-18 (IL-18). 89 – 93 These cytokines play a central role in orchestrating the inflammatory response by recruiting additional immune cells and amplifying the proinflammatory cascade. 57 UA exerts its influence on the renin-angiotensin system through dual mechanisms involving the stimulation of plasma renin activity and renal renin expression. Additionally, UA contributes to the activation of the intrarenal angiotensin system. 94 These immune inflammatory pathways, particularly those involving monocytes and macrophages, are upregulated in the presence of hyperuricemia. 95 , 96 The pro-inflammatory function of uric acid is critical for revealing its role in various inflammatory conditions, such as gout, cardiovascular disease, and metabolic syndrome. 82 UA was observed to reduce reactive oxygen species (ROS) and interleukin-6 (IL-6) production in macrophages while enhancing fatty acid oxidation (FAO) under inflammatory and hypoxic conditions in vitro. 95 Although the antioxidant properties of uric acid have long been recognized, its pro-inflammatory effects complicate its physiological significance and clinical relevance.

Nitric oxide regulation

Nitric oxide (NO) is a vital signaling molecule produced by endothelial nitric oxide synthase (eNOS) within endothelial cells. It serves as a powerful vasodilator, modulating blood pressure by inducing relaxation in the smooth muscle cells of blood vessel walls. 97 Hyperuricemia, by inducing oxidative stress and inflammation, diminishes the expression of eNOS and the synthesis of NO, while elevating levels of inflammatory cytokines such as IL-6 and TNF- α , ultimately impairing endothelial function. 98 , 99 In addition, NO is involved in inhibiting platelet aggregation, leukocyte adhesion, and inflammation. It also contributes to various signaling pathways that affect cardiac function, nerve conduction, and the immune response. 100 The interaction between uric acid and NO is bidirectional. When concentrations are low, uric acid acts as a natural antioxidant that scavenges free radicals and prevents oxidative damage. Specifically, uric acid neutralizes peroxynitrite, a harmful molecule formed from the reaction between nitric oxide and superoxide radicals. 101 , 102 This antioxidant effect of uric acid protects nitric oxide from degradation by superoxide radicals, thereby indirectly supporting nitric oxide bioavailability and potentially enhancing nitric oxide-mediated vasodilation. 61 , 103 However, at higher concentrations, uric acid reduces NO bioavailability, impairs eNOS function, reduces NO production, and further exacerbates endothelial cell dysfunction. These complex interactions have important implications for cardiovascular health, renal function, and treatment of NO-related diseases. 97 , 104 , 105 Uric acid has a protective effect against dementia and cognitive impairment related to senescence. 72 , 106 – 110 UA endowed with hydrophilic antioxidant properties which can exert a protective influence against Alzheimer’s disease and Parkinson’s disease, while hyperuricemia could potentially worsen vascular dementia, encompassing conditions such as stroke and small vessel cerebrovascular disease. 111

Aging and Anti-aging effects

Uric acid can influence cellular activities, such as cell proliferation, by modulating EGF/EGFR bioactivity. Hyperuricemia can downregulate the expression of cell cycle proteins including D1, p-Rb, Ki67, and CDK4, inducing cellular senescence and consequently diminishing EGF/EGFR signaling. Increased levels of uric acid result in inflammation and oxidative stress, which serve as potential risk factors for cellular senescence, apoptosis, and disruptions in the cell cycle. Conversely, physiological concentrations of uric acid (5 mg/dl) exhibit anti-aging effects by enhancing growth factor activity in aging cells. However, at higher concentrations (10 mg/dl), uric acid promotes cellular senescence and downregulates EGF/EGFR signaling. 112

Immune system interaction effects

The interaction of uric acid with the immune system involves the formation of monosodium urate (MSU) crystals. These uric acid crystals activate pattern recognition receptors (PRRs), including Toll-like receptors (TLRs), NOD-like receptors, and the NLRP3 inflammasome. 113 – 116 Activation of these receptors initiates an inflammatory signaling cascade resulting in the secretion of pro-inflammatory cytokines and chemokines. These needle-shaped crystals can accumulate in diverse tissues, particularly in joints, eliciting an innate immune response. Consequently, immune cells, notably neutrophils and macrophages, are recruited to sites of crystal deposition. 10 Moreover, neutrophils can phagocytose uric acid crystals and release various inflammatory mediators, such as interleukin-1β and ROS, further activating inflammation and amplifying the local inflammatory response. 113 Studies have shown that UA also affects both T-cell populations and regulatory T-cell populations. 117 UA-induced inflammation leads to the recruitment and activation of effector T cells at the site of crystal deposition, thereby exacerbating local inflammation. 113 , 117

The physiology of Hyperuricemia

Hyperuricemia is characterized by an elevated level of uric acid in the bloodstream, often surpassing the normal physiological threshold. This metabolic state arises from a dysregulation between uric acid production and elimination, culminating in its accumulation in the bloodstream. 118 The etiology of hyperuricemia is multifaceted and involves genetic predispositions, environmental factors, and complex metabolic pathways governing urate homeostasis.

Factors influencing uric acid

The risk of developing hyperuricemia is influenced by a combination of inherited genetic variants, environmental factors, gene-environment interactions, and intrinsic factors such as age, sex, and body weight. 119 Research indicates that factors such as age, diet, alcohol consumption, fructose-rich intake, pharmacologic interventions and diseases, such as obesity, insulin resistance, Down syndrome, and kidney disease, contribute to the development of hyperuricemia 120 – 124 (Fig. ​ (Fig.2 2 ).

Consumption of purine-rich meats such as beef, pork, lamb, and seafood like oysters, shrimp, and tuna, as well as dietary fructose, are known to elevate uric acid (UA) production. Additionally, alcohol metabolism from beer and distilled spirits, along with certain medical conditions such as tumor lysis syndrome and obesity, pose increased risks for hyperuricemia. Hepatic metabolism of uric acid involves the sequential processing of purine nucleotides, including adenosine monophosphate (AMP), guanosine monophosphate (GMP), and inosine monophosphate (IMP). 66 IMP plays a pivotal role as a key intermediate in purine nucleotide biosynthesis, serving as a precursor for the synthesis of both adenosine monophosphate (AMP) and guanosine monophosphate (GMP). Moreover, IMP can be enzymatically deaminated by IMP dehydrogenase, leading to the formation of inosine. Inosine, in turn, can undergo phosphorylation to become hypoxanthine. Hypoxanthine undergoes oxidative reactions catalyzed by xanthine oxidase (XOD), resulting in the production of xanthine. Xanthine can further undergo oxidation reactions, also catalyzed by XOD, ultimately leading to the formation of uric acid from xanthine. 118 However, xanthine oxidase inhibitors, such as allopurinol, febuxostat, and topiroxostat, serve as first-line therapies by effectively reducing the production of uric acid from both endogenous and dietary purine sources. In the final step of purine metabolism, the enzyme uricase converts uric acid into allantoin, a highly soluble compound. While humans lack the uricase enzyme, animals naturally possess it. The therapeutic agents pegloticase and rasburicase are recombinant forms of uricase, designed to facilitate the breakdown of uric acid in humans

Dietary selections abundant in purine, particularly nucleic acids, notably contribute to the production of uric acid. Beverages like beer, which contains purine-rich yeast, along with the consumption of foods such as bacon, beef, lamb, turkey, veal, venison, organ meats, and certain types of fish and shellfish (including anchovies, cod, tuna, sardines, shrimp, scallops, trout, and haddock), are implicated in elevating uric acid levels. 101 , 125 Beer contains high amounts of guanosine, and ethanol increases the degradation of ATP. Alcohol and dietary purines (meat, seafood) may be risk factors for gout, which has traditionally been considered a disease of affluence. Sugar (sucrose) is a disaccharide composed of glucose and fructose. 126 Among middle-aged Chinese men, a direct and notable association exists between seafood consumption and the occurrence of hyperuricemia. Conversely, protein intake from either animal or plant sources demonstrated a contrasting impact on the prevalence of hyperuricemia. Nevertheless, comprehensive data on the precise purine content of foods remains limited, primarily due to various factors such as food processing techniques, which can influence purine levels. 121 According to the NHANES, dietary folate intake reduces the risk of hyperuricemia in female, while vitamin B12 and folate intake are associated with a reduced risk of hyperuricemia in men. 127

Fructose metabolism

Fructose metabolism, particularly through the aldolase reductase pathway in the liver, results in increased UA levels. 128 Fructose is transported into cells via SLC2A5 (Glut5) and undergoes metabolism to fructose 1-phosphate catalyzed by ketohexokinase (KHK), a process requiring ATP. This metabolic pathway primarily occurs in the liver, leading to a transient reduction in intracellular ATP and phosphate levels. Subsequently, activation of adenosine monophosphate (AMP) deaminase occurs, with AMP generated from fructose metabolism entering the purine catabolic pathway, ultimately resulting in the production of uric acid. 129

Purine metabolism

Uric acid originates from the breakdown of purines catalyzed by the oxidized and reduced forms of xanthine oxidoreductase (XOR) and xanthine dehydrogenase (XDH). Purines are essential nucleotide components of DNA and RNA, crucial for cell division and metabolism. 101 Both endogenous purine metabolism and dietary intake contribute to uric acid production. Increased cellular catabolism, heightened endogenous purine synthesis, and a diet rich in purines can elevate urate levels. Although basal XOR expression is typically low in humans, various factors such as hypoxia, ischemia-reperfusion injury, interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and corticosteroid treatment can markedly enhance XOR transcription. Additionally, the conversion of XDH to XO is expedited under hypoxic conditions. 101 Purine metabolism occurs primarily in the liver and in tissues where xanthine oxidase is widely distributed. Approximately 65% of uric acid is excreted from the kidneys, and the rest is excreted mainly into the intestine. 130 Due to the absence of the uricase enzyme responsible for converting uric acid into allantoin and allantoic acid, UA remains the terminal metabolic product in humans. The majority of uric acid is filtered in its free form, with approximately 90% of the filtered UA being reabsorbed. 131 Hyperuricemia can be triggered by inadequate excretion due to reduced glomerular filtration, impaired tubular secretion and improved tubular reabsorption. 39 , 40 Elevated phosphoribosyl pyrophosphate (PRPP) synthetase activity and deficiency in hypoxanthine phosphoribosyl transferase (HPRT) not only enhance endogenous purine synthesis but also result in excessive production and buildup of uric acid. 132 , 133

Cellular turnover processes like tumor lysis, rhabdomyolysis, and hemolysis contribute to increased urate production. Additionally, various transporters in the intestinal mucosa and salivary glands, diverse medications, extracellular fluid volume depletion, and organic acids that facilitate transport can influence uric acid metabolism. Thus, both intrinsic and extrinsic factors play roles in urate production. 134

Uric acid regulation

UA levels are contingent on the dynamic equilibrium among purine-rich food intake, endogenous urate synthesis, and urate excretion through various routes, including urine and the gastrointestinal tract. Disruptions to this balance can impact serum uric acid (SUA) levels. 135 – 137 The transport of uric acid entails multiple genes and proteins, collectively participating in the complex mechanisms of uric acid reabsorption and secretion. At a genome-wide significant level, three loci (ABCG2, SLC2A9, and CUX2) have been identified in association with renal urate overload, whereas four loci (ABCG2, SLC2A9, CUX2, and GCKR) have been linked to renal urate underexcretion. 138 , 139 The main transporter genes are SLC22A12 (URAT1), SLC2A9 (GLUT9), and ABCG2 (BCRP). 140 (Table ​ (Table2) 2 ) It is increasingly recognized that disturbances in urate transport, both in the gastrointestinal tract and kidneys, are pivotal in the pathogenesis of diseases associated with hyperuricemia. Investigating these transporters and their genetic loci is essential for regulating and achieving target serum urate levels. Moreover, alterations in gut microbiota structure or imbalance can contribute to metabolic disorders, influencing the synthesis of purine-metabolizing enzymes and the release of inflammatory cytokines. This relationship is closely linked to the onset and progression of hyperuricemia and gout, which are metabolic immune disorders. 141 , 142

Urate transporters and their characteristics related to launched therapies for hyperuricemia

Gut microbiota

UA serves as both an antioxidant and an immune modulator, exerting significant influence on the composition of the gut microbiota. Notably, the gastrointestinal tract plays a pivotal role as a pathway for uric acid excretion, with the microbial ecosystem within the gut intricately involved in this metabolic process. 143 Transporters for uric acid located in intestinal epithelial cells facilitate the translocation of uric acid from the bloodstream into the intestinal lumen. 144 – 152 Once in the intestinal lumen, UA can either be directly excreted or metabolized by the gut microbiota. 153 Specific bacteria, such as Lactobacillus and Pseudomonas, participate in the degradation and elimination of uric acid in the intestine through the production of short-chain fatty acids (SCFAs). 154 Moreover, the activities of enzymes involved in uric acid metabolism are intricately connected to the gut microbiota. 155 – 157 Uricase, an enzyme responsible for converting UA into allantoin and urea, is found in various bacterial species including Bacillus pasteurii, Proteus mirabilis, and E. coli. Certain strains of Lactobacillus, such as Lactobacillus sp. OL-5, Lactobacillus plantarum Mut-7, and Lactobacillus plantarum Dad-13, have been found to exhibit higher intracellular uricase activity, further emphasizing the role of gut microbiota in UA metabolism. 143 , 149 , 154 An imbalance in the gut microbiota can elevate uric acid concentrations, thereby exacerbating the chronic deposition of UA crystals in joints, characteristic of gout. This dysbiosis typically involves a proliferation of opportunistic pathogens alongside a reduction in beneficial bacteria known to stimulate the synthesis of anti-inflammatory cytokines. 145 , 158 , 159 The exploration of intestinal flora metabolism represents a promising frontier in clinical research pertaining to hyperuricemia and gout. Metabolic research has established a correlation between hyperuricemia and disruptions in the primary bile acid pathway or intestinal metabolism, suggested that targeting the gut microbiome could offer innovative therapeutic approaches for managing hyperuricemia and its associated complications. Future studies will concentrate on unraveling the intricate mechanisms through which gut microbiota modulates metabolic processes in these patient populations.

Genetics of urate control

Hyperuricemia and hyperuricosuria have been shown to cluster in families, indicating a familial transmission pattern. Studies in South American ethnic groups have demonstrated heritability rates ranging from 39% to 45%. 160 – 165 Both adults and children have been found to exhibit genetic mutations that affect baseline renal urate excretion levels. In a genome-wide association study (GWAS) involving more than 140,000 individuals of European descent, uric acid receptors encoded by twenty-eight chromosomal genes were discovered to impact plasma uric acid levels. Genetic variants associated with uric acid levels mainly include purine metabolism (e.g., XDH, HPRT1), urate transporters (e.g., SLC2A9, SLC22A12), and renal urate processing regulators (e.g., ABCG2). 119 , 166 , 167 Single nucleotide polymorphisms (SNPs) within or near these genes have consistently shown associations with variations in uric acid levels across diverse populations. 168 Genome-wide association studies (GWAS) have identified key loci housing urate transporters crucial for uric acid excretion in both renal and gastrointestinal pathways. 167 , 169 Through functional insights and expression quantitative trait loci (eQTL) analyses, several loci have identified probable causal genes, such as SLC2A9, ABCG2, PDKZ1, SLC22A11 (OAT4), and INHBB. 166 Additionally, numerous other loci have strong candidate genes identified, including GCKR, RREB1, SLC17A1 to SLC17A4, SLC22A12, MAF, MLXIPL, PRKAG2, HNF4G, A1CF, IGFR1, and HLF. 166 , 170 (Fig. ​ (Fig.3) 3 ) The primary physiological regulation of serum uric acid levels occurs through renal excretion. 171 GWAS in major populations consistently highlight urate transporter genes as pivotal loci influencing serum uric acid levels, 138 , 139 notably SLC2A9 (GLUT9) and SLC22A12 (URAT1), involved in urate reabsorption from urinary filtrates. 172 , 173 For instance, the primary effect of SLC2A9 (rs12498742) explains 2% to 3% of serum uric acid level variance in Europeans, which is substantial for a complex phenotype. 174 , 175 Variation in ABCG2 (BCRP) is also noteworthy across European and East Asian populations. 176 – 178 Notably, in individuals of European ancestry, the genetic control of SLC2A9a and SLC2A9b isoforms, situated at basolateral and apical membranes respectively, constitutes a prominent genetic signal. 172 , 174 Thus, we concluded several key genes have been identified with significant associations with SUA levels. Among these genes, ABCG2 stands out as one of the most crucial and strongly linked to SU levels to the risk of hyperuricemia. 167 , 171 , 179 , 180 A specific polymorphism (rs2231142) within ABCG2 has been identified, which reduces urate efflux activity and increases the susceptibility to both HU and gout. 181 Notably, this variant is more prevalent in Asian populations compared to Europeans. 180 , 182 Another important gene, SLC2A9, encodes a urate transporter and exerts a significant influence on SUA levels. A specific polymorphism (rs734553) within SLC2A9 has been associated with an elevated risk of hyperuricemia. 119 , 166 Interestingly, the prevalence of this variant varies among different populations, with higher frequencies observed in Asian populations. Research indicates that the rs1967017 variant in PDZK1 creates a binding site for the transcription factor hepatocyte nuclear factor 4α (HNF4α) within an enhancer region upstream of the PDZK1 transcription start site. 170 This binding increases PDZK1 expression, potentially leading to reduced urate excretion. Another prominent genetic variant associated with serum urate levels is rs1263026 at GCKR. 183 The Leu allele of this variant induces relaxation of glucokinase inhibition, resulting in heightened glucose phosphorylation. This process diminishes the ATP pool and augments urate production through ADP catabolism. 184 However, other loci with more modest effects have not consistently replicated in subsequent studies examining their correlation with serum urate levels.

In East Asian populations, four loci have demonstrated a significant association with serum urate levels: SLC2A9, ABCG2, SLC22A12, and MAF. Similarly, in African American populations, three loci have been identified: SLC2A9, SLC22A12, and SLC2A12. In contrast, the European population predominantly shows an association with only one locus, SLC2A9. Australian studies have identified 28 loci, encompassing all but one (SLC2A12) of those found in African American and East Asian populations. Among these diverse populations, certain loci, such as SLC2A9, ABCG2, GCKR, and SLC17A1-SLC17A4 (also known as NPT1-NPT4), exhibit stronger effects and have been consistently replicated in multiple studies

URAT1, located in the membrane of renal tubular epithelial cells, serves as a uric acid transporter protein. It plays a crucial role in mediating UA reabsorption, a process in which approximately 90% of uric acid is typically reabsorbed following glomerular filtration. 175 URAT1 belongs to the organic anion transporter (OAT) subgroup within the broader gene family. Other subcategories within this family include organic cation transporters, as well as novel type/carnitine transporters. Moreover, additional genetic alterations in hyperuricemia and gout associated with PDZK1 likely occurs through its modulation of the apical membrane localization of URAT1. 55 Research has shown that individuals with renal hypouricemia and loss-of-function mutations in URAT1 demonstrate incomplete responses to both pyrazinamide and uricosurics, resulting in average concentrations reaching 0.93 mg/dL. 185

GLUT9 functions as the principal transporter for urate efflux across the basolateral membrane of the proximal tubule in the kidney, facilitating transepithelial urate absorption. 186 The pronounced lack of renal reabsorption of filtered urate in hypouricemic patients with GLUT9 loss-of-function mutations provides compelling evidence of the critical role this protein plays in renal tubular urate reabsorption. In these individuals, the fractional excretion of urate approaches 150%, highlighting the predominant mechanism of tubular urate secretion in the absence of reabsorption. 134

BCRP is an efflux pump that is driven by ATP on the apical membrane proximal renal tubule and intestinal epithelial cells and is critical for UA excretion. Mutated or dysfunctional ABCG2 may lead to significantly reduced excretion, moderate hyperuricemia and metabolic syndrome. 139 Initially, it was hypothesized that the loss or reduction of ABCG2-mediated renal urate secretion would result in increased renal urate reabsorption, as diminished renal excretion is typically considered the primary mechanism of hyperuricemia in most gout patients. However, hyperuricemic patients with varying degrees of ABCG2 dysfunction, categorized by genotypes of dysfunctional SNPs, exhibit hyperuricemia characterized by urate overproduction. This is evidenced by elevated urinary urate excretion and a fractional excretion exceeding 5.5%. Additionally, ABCG2 dysfunction appears to contribute to renal underexcretion of urate in patients with milder functional impairments, also classified by genotype. 136

OAT1, OAT3 and OAT4

OAT1 and OAT3, located on the basolateral membrane of the proximal tubule, function as urate/dicarboxylate exchangers responsible for uric acid excretion. Additionally, OAT4 participates in the transport of high-affinity binding steroids such as estrone sulfate (ES). 187 This transporter operates as a chloride-ion-dependent exchanger for both ES and uric acid. Physiologically, OAT4 facilitates uric acid excretion in the proximal tubule by orchestrating ion exchange processes such as PAH/Cl-, PAH/ES, and potentially PAH/UA interactions. Its interplay with NHE3 and sodium dicarboxylate transporter 1 contributes to the regulation of intracellular α-ketoglutarate levels. 134

NPT1 and NPT4

NPT1, which exhibits a weak to moderate correlation with altered uric acid levels, facilitates both the absorption and efflux of urate. It functions as a chloride-dependent urate transporter, which is involved in sodium/phosphate cotransport activities. 188 NPT4 is crucial in urate excretion, working synergistically with basolateral organic anion transporters 1 and 3 (OAT1/OAT3). Uric acid was absorbed by OAT1 and OAT3 into tubular cells, which is subsequently transported into the urinary lumen by NPT4. 189

Polyvalent PDZ domain 1 (PDZK1) is a multidomain protein with four PDZ domains, primarily located at the apical membrane of kidney proximal tubule cells. It is abundantly expressed in this region and engages directly with several apical transporters, such as URAT1 and NPT1. 134 As a scaffold protein, PDZK1 significantly regulates the activity of various transport proteins within the proximal tubules. Additionally, PDZK1 is proposed as a potential upstream regulator of ABCG2, impacting its function in the small intestine. Specifically, the upregulation of ABCG2 expression and function in response to soluble uric acid in intestinal cell lines is dependent on PDZK1 at the transcriptional level. 188

These genes are specifically expressed on the apical membrane of renal proximal tubule cells, which are crucial for the secretion of uric acid into the glomerular filtrate, as depicted in Fig. ​ Fig.4. 4 . Beyond the genes that encode for these transporter proteins, over a hundred genetic loci have been associated with hyperuricemia. Genome-wide association studies provide a comprehensive and unbiased method for pinpointing genetic factors linked to urate regulation and metabolism. 190

Uric acid undergoes a dynamic process of elimination and reabsorption, primarily orchestrated by the kidneys (two-thirds) and the intestines (one-third). In the nephron, filtration of water and solutes occurs within the glomerular capsule, followed by tubular reabsorption, predominantly mediated by the proximal convoluted tubule. Concurrently, tubular secretions extract uric acid from peritubular capillaries, secreting it into the tubular fluid for urinary excretion. Urate transporters in renal proximal tubule epithelial cells actively mediate the secretion and reabsorption of urate, thus determining the net excretion levels from the kidney. In the renal proximal tubule, SLC22A12 (URAT1), SLC17A1 (NPT1), and SLC22A11 (OAT4) located on the apical membrane facilitate reabsorption. SLC2A9 (GLUT9), found in both the apical and basolateral membrane tubules, is a long isoform that mediates the basolateral efflux of urate back into circulation. For excretion, SLC22A6 (OAT1) and SLC22A8 (OAT3) on the basolateral membrane facilitate urate entry into the renal tubules. ABCG2 (BCRP) and SLC17A3 (NPT4), positioned on the apical side, contribute to the secretory transport of urate into the tubule lumen for urinary excretion. In intestinal metabolism, uric acid is actively secreted into the intestinal lumen primarily by the transporter ABCG2, underscoring the role of the intestines in urate homeostasis

Hyperuricemia and diseases

An elevated uric acid concentration above physiological levels can pose a potential risk factor for several diseases closely associated with metabolic disorders. Numerous epidemiological studies have suggested that hyperuricemia may correlate with hypertension, metabolic syndrome, insulin resistance, dyslipidemia, type II diabetes, kidney disease, and cardiovascular events including coronary heart disease and cerebrovascular disease. 191 – 199 Studies have demonstrated that serum uric acid levels can also predict the onset of hypertension, diabetes, obesity, and renal disorders 74 , 200 , 201 (Table ​ (Table3 3 ).

The mechanisms of conditions caused by hyperuricemia

Mendelian randomized studies

A significant biomedical question is whether hyperuricemia is causally associated with related comorbid conditions such as gout, hypertension, cardiac and kidney disease, etc. 202 – 209 Utilizing data from observational epidemiologic studies in conjunction with experimental evidence from in vitro and animal model investigations, elevated serum urate levels have been suggested as being potentially linked to concurrent metabolic disorders. 210 The principles of Mendelian randomization, which leverages genetic variants influencing exposures (e.g., UA levels), can serve as a natural randomization method to study the causal effects of these exposures on disease outcomes. 21 , 211 , 212 To investigate the association between elevated serum urate concentrations and comorbid metabolic conditions, Mendelian randomized studies were conducted using genetic variants linked to increased serum urate levels. 213 – 215 These genetic variants act as proxies for prolonged urate exposure, assuming they remain unconfounded by other factors. 18 , 22 , 206 , 216 The pioneering Mendelian randomization studies leveraged specific genetic variants with substantial impacts on serum uric acid levels as instrumental variables. The objective of their research was to investigate the associations between uric acid concentrations and various health conditions, including body mass index, bone mineral density, coronary artery disease, blood pressure, metabolic syndrome, blood glucose levels, triglyceride levels, diabetes mellitus, serum creatinine levels, estimated glomerular filtration rate, Parkinson’s disease, memory, and gout. 207 , 212 , 217 – 220 However, over the past three years, Mendelian randomization studies have utilized genetic variants associated with serum uric acid levels, identified through genome-wide association studies (GWAS), to construct genetic risk scores. These investigations consistently indicate a lack of evidence supporting a causal relationship between elevated serum urate levels and the risk of developing type 2 diabetes mellitus, coronary heart disease, ischemic stroke, and heart failure. 17 , 221 – 223 Li et al. 22 , 169 conducted a comprehensive analysis of 107 Mendelian randomization studies, included a median of 7,158 participants and 2,225 cases, with serum uric acid level as the exposure variable for various health outcomes. The instrumental variables utilized in these studies explained 2% to 6% of the variability in serum uric acid levels. The results indicated a significant association between serum uric acid levels and four health outcomes: diabetic macrovascular disease, arterial stiffness, renal events, and gout. Particularly noteworthy was the robust association observed with gout. However, the study did not find significant associations with several common cardiac and metabolic disorders, including type 2 diabetes, hypertension, chronic kidney disease, ischemic heart disease, and congestive heart failure. 224 – 238 These findings suggest that while elevated serum uric acid levels may be associated with certain health outcomes such as gout and renal diseases, the evidence does not strongly support a causal relationship with other metabolic disorders. Additional analyses have shown consistent results across most outcomes examined, which included a variety of cardiovascular diseases, such as incidence of atrial fibrillation, 239 coronary heart disease, incidence of hypertension, 216 and incidence of stroke, 71 diabetes, 240 chronic kidney disease, 222 mild cognitive impairment, Parkinson’s disease, 241 and multiple sclerosis. 21 However, statistical significance was inconsistent in the two outcomes of diabetic neuropathy 5 , 218 and Alzheimer’s disease. 242 In particular, the role of genetic variants, such as those within the SLC2A9 gene, in influencing cardiovascular and metabolic outcomes remains subject to debate. 6 , 191 , 223 , 243 , 244 Recent research has delved into the causal relationship between variants of the URAT1 transporter gene (SLC22A12) and obesity and metabolic syndrome. 245 , 246 In a randomized controlled trial involving patients with essential hypertension, specific SLC22A12 single nucleotide polymorphisms (SNPs), such as rs11602903, were associated with higher body mass index (BMI), larger waist circumference, higher HDL cholesterol levels, and the presence of metabolic syndrome in individuals of European descent. 247 – 249 However, these associations were not observed in non-European populations, underscoring potential ethnic differences in genetic susceptibility to hyperuricemia-related metabolic abnormalities. 250 – 252

UA induced inflammation and relative mechanism

Uric acid signaling triggers the activation of several transcription factors, such as NF-κB or AP-1, through the activation of MAPK p38 and ERK pathways, resulting in the production of reactive oxygen species (ROS) under the conditions of hyperuricemia. 78 The NLRP3 inflammasome, part of the nucleotide-binding domain and leucine-rich repeat protein family complex, is essential in the development of numerous infections and inflammatory disorders. 116 , 253 – 256 The expression of NLRP3 is induced by NF-κB activation, leading to the assembly of a complex with the adaptor protein ASC and procaspase-1. 85 , 91 , 114 , 257 Subsequently, procaspase-1 transforms into its mature form, caspase-1. This enzyme then activates pro-IL-1β and pro-IL-18, converting them into their mature forms, IL-1β and IL-18, respectively. This process coincides with the initiation of pyroptosis, facilitating the release of IL-1β into the extracellular environment. 258 , 259 In gout, the activation of the NLRP3 inflammasome by monosodium urate (MSU) crystals stimulates the release of IL-1β, which contributes to the progression of arthritis. This activation mechanism involves phagocytic cells such as macrophages and neutrophils. 260 – 264 This cascade of events leads to enhanced transcription of innate cytokines in various cell types including vascular endothelial cells, smooth muscle cells, and adipocytes. The activation is linked to the generation of vasoconstrictive agents, including MCP-1, (pro)renin receptor, endothelin, and angiotensin II, while concomitantly diminishing vasodilatory compounds like nitric oxide, which may contribute to the development of hypertension and lead to decreased viability of cardiomyocytes and myocardial damage. 94 , 265 – 267 Moreover, in vascular cells, upregulation of growth factors like PDGF has been noted, which can promote smooth muscle cell proliferation and atherosclerosis. 268 In vascular smooth muscle cells, uric acid-induced activation of MAPKs promotes the expression of MCP-1, an important chemokine involved in atherosclerosis progression. In pancreatic β-cells, uric acid triggers ERK activation, resulting in reduced cell viability, apoptosis, and the production of reactive oxygen species. 78 , 269 , 270 Treatment with a URAT1 inhibitor suppresses the ERK pathway and mitigates uric acid-induced cell damage, underscoring the involvement of intracellular uric acid in MAPK activity. 271 – 274 Additionally, uric acid regulates MAPK through phosphatase activity that inhibits the MAPK pathway. 275 , 276 Monosodium urate crystals are ingested by monocytes via phagocytosis, engaging Toll-like receptors (TLRs) such as TLR2 and TLR4. This interaction prompts the recruitment of the adaptor protein ASC to the NLRP3 inflammasome complex. Subsequently, caspase-1 is drawn to the ASC assembly, where it oligomerizes along the ASC filaments. This oligomerization triggers the autoproteolytic maturation of caspase-1, activating its inflammatory caspase function. 183 , 277 Active caspase-1 then catalyzes the proteolytic cleavage and maturation of proIL-1β into the biologically active IL-1β, which leads to acute flares of gouty arthritis. 183 In neutrophils, uric acid activates the ERK/p38 signaling pathway while inhibiting the Nrf2 pathway. Additionally, monosodium urate crystals induce the translocation of Nrf2 into the nucleus and modulate intracellular reactive oxygen species levels, thereby promoting the activation of the NLRP3 inflammasome. This ROS-induced injury can lead to apoptosis, disruptions in ion regulation, and mitochondrial dysfunction, further exacerbating the inflammatory response and tissue damage. 67 , 278 Furthermore, resolution of gout flares involves the formation of neutrophil extracellular traps, which capture monosodium urate crystals. Uric acid can modulate cytokine production and inflammatory outcomes through various pathways. 253 , 279 , 280 Uric acid can enhance AKT phosphorylation, which subsequently leads to PRAS40 phosphorylation with the activation of mTOR, 281 resulting in the inhibition of autophagy, as well as inhibiting AMPK phosphorylation. 282 When UA levels are elevated, RAGE signaling is stimulated, leading to the activation of nuclear factor-kappa B (NF-κB). NF-κB activation triggers the transcription and release of pro-inflammatory cytokines within endothelial cells. Additionally, UA-induced activation of RAGE promotes the expression and extracellular release of high mobility group box 1 protein (HMGB1) by endothelial cells, lymphocytes, monocyte-derived macrophages, and vascular smooth muscle cells. 87 , 283 , 284 The interaction between HMGB1 and RAGE amplifies the inflammatory cascade, contributing to cell apoptosis and endothelial dysfunction, resulted to CVD or CKD. 277 , 285 This dysregulation of the HMGB1-RAGE pathway further diminishes NO availability, exacerbating inflammation. Moreover, UA-induced inflammation and oxidative stress can also trigger endoplasmic reticulum (ER) stress, decreased nitric oxide bioavailability and produce peroxynitrite (ONOO-), a very powerful radical, which contributing to cellular dysfunction and apoptosis. 61 , 103 , 270 , 282 Uric acid diminishes nitric oxide levels through several mechanisms, including the consumption of NO due to excessive reactive oxygen species production and direct inhibition of NO synthesis. UA-induced dephosphorylation of endothelial NO synthase (eNOS) via uric acid transporters reduces NO production in human umbilical vein endothelial cells. Moreover, the HMGB1-receptor for advanced glycation end products pathway regulates eNOS production 14 , 98 , 286 , 287 (Fig. ​ (Fig.5 5 ).

The role of uric acid in the pathogenesis of hyperuricemia and its associated diseases involves complex intracellular signaling mechanisms. Elevated intracellular uric acid levels stimulate the production of reactive oxygen species and activate multiple inflammatory signaling pathways. XO xanthine oxidase, eNOS endothelial nitric oxide synthase, MSU monosodium urate, Nrf2 Nuclear factor-erythroid 2-related factor 2, mTOR mammalian target of rapamycin complex, ERK extracellular signal-regulated kinase, AMPK AMP-activated protein kinase, IL-1β interleukin-1β, MAPK mitogen-activated protein kinases, PRAS40 Proline-Rich AKT Substrate, NF-κB nuclear factor κB, TLR Toll-like receptors, NLRP3, NOD-, LRR- and pyrin domain-containing 3, PKC Protein Kinase C, RAGE Receptor for Advanced Glycation End Products pathway

Biomarkers of hyperurceimia and its relative disease

Recent advances in proteomics have shed light on the biochemical underpinnings of hyperuricemia. Notably, Liu’s 288 research indicated elevated serum levels of complement C3, haptoglobin, complement C4, and apolipoprotein A1 (apo A1) in Uyghur patients with hyperuricemia. This suggests a correlation between hyperuricemia and high-density lipoprotein (HDL) components, with apo A-I implicated in cholesterol transport and anti-atherosclerotic properties. 289 – 291 Furthermore, HDL’s role in lipid metabolism regulation and its influence on cardiovascular disease and diabetes development cannot be overlooked. 292 The inhibition of apo A-I may be linked to atherosclerosis progression through chronic inflammation pathways. Moreover, the complement system’s activation in response to hyperuricemia has been implicated in the pathogenesis of various inflammatory conditions, including gout, renal injury, and type 2 diabetes (T2DM). 144 The NLRP3 inflammasome’s activation and its interplay with the complement and coagulation systems are of particular interest. Component C5a of the complement system, recognized for its potent pro-inflammatory effects, can amplify monocyte and neutrophil activation. MSU crystals have been shown to trigger IL-1β production and inflammatory cytokine release through C5a activation, highlighting the potential of complement antagonists in managing gout inflammation. In the realm of urine proteomics, Huo et al. 293 conducted a comparative study between healthy individuals and those with hyperuricemia, revealing differentially expressed proteins that hint at pathways involved in insulin receptor recycling and lipid metabolism. The study pinpointed the V-type proton ATPase subunit B kidney isoform and Complex Factor D (CFAD or adipsin) as key factors impacting insulin regulation in hyperuricemia patients.

Cardiovascular metabolic mechanisms and diseases

In recent years, numerous studies have reinforced the strong association between hyperuricemia and cardiovascular events. Research has demonstrated that serum uric acid levels are positively correlated with hypertension. 265 , 294 , 295 The proposed mechanisms involve the activation of the renin-angiotensin system, inflammatory responses, oxidative stress, vascular smooth muscle cell proliferation, and insulin resistance. 57 , 69 , 78 , 94 , 296 The ONATA study showed a negative correlation between serum uric acid levels and insulin sensitivity, suggesting a potential link between uric acid, insulin sensitivity, and the risk of developing hypertension. 105 , 212 Hyperuricemia frequently coexists with insulin resistance, which can elevate the activity of the renin-angiotensin-aldosterone system and the sympathetic nervous system. This interaction leads to sodium retention, increased blood volume, and subsequent hypertension. 297 , 298 In patients with hyperuricemia, elevated serum levels of high-sensitivity C-reactive protein (hs-CRP) are closely linked to inflammation and oxidative stress, which may exacerbate hypertension. 299 Soluble urate may further exacerbate vascular inflammation and oxidative stress by promoting LDL oxidation, lipid peroxidation, and elevating hs-CRP levels. Moreover, hs-CRP can contribute to vascular endothelial injury by activating the complement system. 99 , 287 Furthermore, elevated uric acid levels have been implicated in causing inflammation in endothelial cells via the activation of the receptor for advanced glycation end products (RAGE) signaling pathway. 285 When UA levels are increased, RAGE signaling becomes activated, that ultimately lead to endothelial dysfunction, is a key feature of various cardiovascular diseases. Specifically, the activation of RAGE triggers the nuclear factor-kappa B pathway, resulting in the transcription and release of proinflammatory cytokines within endothelial cells. 277 , 285 To mitigate UA-induced endothelial dysfunction and inflammation, targeting the RAGE signaling pathway offers a promising therapeutic strategy. Employing anti-RAGE antibodies to inhibit RAGE activity can suppress the HMGB1/RAGE signaling axis, thereby alleviating endothelial dysfunction and diminishing inflammation within endothelial cells. 285 , 300 , 301 (Fig. ​ (Fig.5) 5 ) By modulating this pathway, it may be possible to alleviate the detrimental effects of elevated UA levels on endothelial function and reduce associated cardiovascular risks. 105 , 265 , 302

Elevated serum uric acid levels heighten the risk of cardiovascular disease (CVD) mortality, potentially due to mechanisms by which hyperuricemia activates the renin-angiotensin system and induces hypertension. Additionally, uric acid has been detected in atherosclerotic plaques. 102 , 201 A recent study conducted in the Japanese revealed that even among healthy, lean, normotensive individuals, the presence of hyperuricemia is associated with an elevated risk of cardiometabolic disease. 191 Kleber et al. reported a significant association between each 1 mg/dL increase in genetically predicted uric acid concentration and the risk of cardiovascular death and sudden cardiac death. 207 Emerging evidence has linked elevated serum uric acid levels to cardiovascular diseases, particularly atherosclerosis and hypertension. Chronic low-grade inflammation is a hallmark of atherosclerosis, and UA-induced IL-1β release may contribute to this inflammatory milieu. 69 , 90 , 239 , 303 Additionally, uric acid has been associated with endothelial dysfunction, which further exacerbates vascular inflammation and contributes to hypertension. 237 , 304 – 308 Endothelial dysfunction characterized by impaired nitrogen oxide-mediated vasodilatation is a key event in the development of atherosclerosis. 94 Experimental and clinical research has substantiated that elevated uric acid levels exert detrimental effects on cardiovascular health, with increased oxidative stress being a key mechanism implicated in these adverse outcomes, 6 , 66 decreased nitric oxide availability, endothelial dysfunction, the promotion of local and systemic inflammation, vasoconstriction, vascular smooth muscle cell proliferation, insulin resistance 309 and metabolic disorder. 51 , 124 Additionally, endothelial dysfunction associated with elevated serum uric acid levels leads to a low-grade inflammatory state and vascular activation of the angiotensin system. As estrogen production declines with age in females, its cardio-protective effects may diminish, thereby increasing susceptibility to elevated uric acid levels. 307

Renal metabolic mechanisms and diseases

Emerging evidence increasingly supports the pathogenic role of hyperuricemia in both the onset and progression of chronic kidney disease (CKD). Untreated hyperuricemia is notably acknowledged as a risk factor for the development of CKD. In China, the prevalence of hyperuricemia among CKD patients varies from 36.6% to 50%, with a notable rise observed as CKD progresses. 310 The mechanisms by which hyperuricemia contributes to chronic kidney disease include renal inflammation, endothelial dysfunction, and activation of the renin-angiotensin system. 13 Hyperuricemia is known to stimulate the renin-angiotensin system and impair endothelial nitric oxide release, which collectively lead to renal vasoconstriction and increased blood pressure. 100 Nitric oxide (NO) plays a crucial role in regulating vascular endothelial cell relaxation, maintaining stable renal vascular tone, and influencing renal blood flow, renin secretion, and tubuloglomerular feedback mechanisms. 105 , 311 However, hyperuricemia inhibits nitric oxide synthase, leading to reduced nitric oxide levels. 312 Furthermore, endothelial cells respond to hyperuricemia by upregulating angiotensin-converting enzyme activity, which enhances angiotensin II and superoxide anion production. This cascade promotes vasoconstriction and hypertension. 102 , 313 Uric acid directly affects endothelial cells by reducing nitric oxide levels, influencing processes such as vascular smooth muscle cell proliferation, extracellular matrix deposition, and the adhesion and migration of macrophages. 102 , 227 , 228 , 314 – 317 These effects lead to arterial resistance and remodeling, ultimately contributing to renal dysfunction and fibrosis. 6 , 318 However, the evidence supporting the treatment of asymptomatic hyperuricemia in hypertensive patients with chronic kidney disease is limited. Observational studies have produced inconsistent findings, and there is a notable absence of large-scale randomized controlled trials to validate the efficacy of lowering uric acid levels. Despite these limitations, the majority of existing studies suggest that therapies aimed at reducing uric acid levels may potentially attenuate the progression of CKD. 102 , 319 – 321 A single-center double-blind, randomized, parallel placebo-controlled study found that uric acid reduction slowed the decline of glomerular filtration rate in patients with stage 3 and 4 CKD. 322 Another study by Jeong et al. demonstrated that febuxostat treatment to reduce serum uric acid levels tended to reduce renal functional deterioration in patients with both CKD and hyperuricemia. 323 These findings suggest that reducing uric acid levels could potentially improve renal function. However, ongoing debate centers on whether the benefits of uric acid-lowering therapy stem from decreased uric acid levels or the inhibition of XO activity. 319 , 324 , 325 Further investigations have shown that medications like benzbromarone and febuxostat can mitigate the advancement of chronic kidney disease and decrease serum uric acid levels in CKD patients, highlighting the potential advantages of treatments aimed at lowering uric acid levels. 319 , 326 – 328

Increased uric acid levels are linked to kidney inflammation and the progression of kidney diseases, especially in the presence of hyperuricemia. Gout has been identified as an independent risk factor for chronic kidney disease, nephrolithiasis and acute kidney injury, wherein uric acid excretion by the kidneys participate in facilitating crystal-induced direct tubular toxicity. 310 This finding underscores the close interconnection between uric acid and nitric oxide regulation in this particular clinical context. 329 Kidney damage mediated by UA involves the stimulation of the renin-angiotensin-aldosterone system. In the medulla, an elevated UA concentration results in the deposition of urate precipitates and the activation of the Nod-like receptor protein 3 (NLRP3) inflammasome. 96 Activation of these pathways leads to chronic interstitial inflammation and tubular damage, ultimately contributing to kidney fibrosis. Additionally, in the renal cortex, hyperuricemia amplifies the activity of the renin-angiotensin-aldosterone (RAA) system, fostering sustained vasoconstriction of the afferent arterioles. 130 In turn, leads to glomerular damage and the development of glomerulosclerosis. 330 CKD is characterized by endothelial dysfunction and NO deficiency; thus, uric acid is a potential contributor to CKD progression. It is primarily driven by the development of hypertrophy in the afferent arteriole, which compromises autoregulation and facilitates heightened transmission of systemic blood pressure to the glomerulus. 310 The kidney’s susceptibility to oxidative stress stems from various sources including the mitochondrial respiratory complex, NADPH oxidases, endothelial nitric oxide synthase (eNOS), myeloperoxidase, and xanthine oxidoreductase (XOR), all of which contribute to the advancement of chronic kidney disease and its related complications. 331 Oxidative stress is a characteristic feature of chronic kidney disease, initiating inflammation and endothelial dysfunction, which accelerates arteriosclerosis. This sequence plays a role in glomerular injury, leading to albuminuria and eventual glomerulosclerosis. Hyperuricemia exacerbates oxidative stress, thereby intensifying inflammation and endothelial dysfunction within this context. 332

Gout and its mechanism

Gout is one of the most common forms of chronic degenerative disease of the joints. 333 , 334 It is defined by recurring episodes of inflammatory arthritis affecting joints and specific soft tissues, including cartilage, synovial bursae, and tendons, particularly in the lower extremities, due to the deposition of uric acid in the form of monosodium urate crystals. 34 The painful pathological state of gout is mainly induced by hyperuricemia with the concentration of more than 6.8 mg/dL under physiological conditions (37 ◦C, pH 7.4). 333 , 334 When uric acid levels increase to such concentration, crystals form in the joints, triggering an inflammatory response. MSU crystals display a triclinic structure composed of stacked sheets of purine rings, forming needle-shaped crystals observable under microscopy. The exposed, charged surfaces of these crystals are thought to promote interactions with phospholipid membranes and serum factors, thereby contributing to the inflammatory response mediated by these crystals. 335 MSUs serve as the primary stimuli for initiating, amplifying, and sustaining the innate immune response. They are phagocytosed by macrophages as foreign particles and recognized by Toll-like receptors 2 and 4 (TLR2/TLR4), which subsequently activate and oligomerize the NLRP3 complex. 336 The NLRP3 complex, a multiprotein assembly with proteolytic activity, facilitates the conversion of the pre-IL-1β into its active form, IL-1β. Subsequently, IL-1β is released into the extracellular milieu, initiating acute inflammation. 337 The MSU crystals are initially engulfed by macrophages, which then facilitate the assembly and activation of the NLRP3 inflammasome, preceded by priming through pathways that activate NF-κB, such as those initiated by the engagement of Toll-like receptors (TLRs) within the TLR family. 338 – 340 Inflammasomes are intracellular multiprotein complexes that trigger inflammatory responses. These structures emerge as intracellular pattern recognition receptors (PRRs) like NLRP3 detect signals that have infiltrated the cell’s cytosol. 341 The recognition triggers the PRR to oligomerize and associate with a complex comprising adaptor proteins and effector enzymes. 342 – 344 The formation of the NLRP3 inflammasome involves the recruitment of the adaptor protein ASC, which is then followed by the recruitment of caspase-1. 345 Following initial oligomerization within the inflammasome structure, ASC monomers can subsequently polymerize into high-molecular-weight aggregates. 341 , 346 The recruitment and oligomerization of caspase-1 by this complex initiate the activation and proteolytic cleavage of its substrates. Caspase-1 activates proinflammatory cytokines such as IL-1β by cleaving their respective precursor proteins and proIL-1β. 262 In gout, the release of IL-1β mediated by inflammasomes triggers a significant inflammatory response characterized by vasodilation and rapid recruitment of neutrophils to the site of crystal deposition, thereby driving acute inflammatory episodes. 347 – 349 Similarly, MSU promotes the expression of other cytokines, such as interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and interferon gamma (IFN-γ), and chemokines, such as monocyte chemotactic protein-1 (MCP-1). MCP-1 induces the recruitment of innate immune cells and indirectly affects gout progression. 214 Flare resolution involves the capture of MSU crystals by neutrophil extracellular traps. 350

Diabete and its mechanism

Chronic hyperuricemia is associated with pancreatic β-cell dysfunction, which is a critical component of type 2 diabetes. 4 Research indicates that the likelihood of developing diabetes rises by 6% with each 1 mg/dL increment in uric acid concentration. 240 Uric acid has been observed to adversely affect β-cells, resulting in impaired insulin secretion and decreased functional β-cell mass. This contributes to an insufficient compensatory response to insulin resistance and gluconeogenesis, mediated by the inhibition of hepatic AMP-activated protein kinase, thereby promoting the progression towards overt diabetes. 351 Uric acid can promote oxidative stress, generating reactive oxygen species that cause cellular damage. 122 Oxidative stress is closely associated with insulin resistance and β-cell dysfunction. The increased oxidative load in hyperuricemia may impair insulin sensitivity and exacerbate the metabolic disorders observed in diabetes. 309 Moreover, hyperuricemia frequently coincides with low-grade inflammation. Increased uric acid concentrations have been implicated in the release of inflammatory cytokines, thereby contributing to systemic inflammation. Inflammation is a well-recognized contributor to the pathogenesis of insulin resistance and type 2 diabetes. This inflammatory environment disrupts insulin signaling pathways and exacerbates glucose intolerance. Elevated insulin levels, stemming from insulin resistance and β-cell dysfunction, may enhance the renal reabsorption of uric acid. Consequently, this cycle potentially reinforces higher serum uric acid levels, establishing a feedback mechanism in the interplay between hyperinsulinemia and hyperuricemia. 352 Additionally, research has shown that elevated uric acid levels inhibit insulin-induced glucose uptake in cardiomyocytes. This effect is primarily mediated by an increase in the phosphorylation of insulin receptor substrate 1 (IRS1) and a concomitant inhibition of Akt phosphorylation, a crucial component of the insulin signaling pathway. 353 Moreover, clinical research has identified a correlation between hyperuricemia and diabetes, although the causal relationship remains controversial. While high UA may accelerate the development of diabetes and impair glucose tolerance, it is insufficient to solely induce diabetes. 19 , 351 , 354

Metabolic syndrome (MetS) and its mechanism

Metabolic syndrome is characterized by a cluster of conditions, including obesity, insulin resistance, and dyslipidemia, and is intimately linked to chronic inflammation. 355 The prevalence of metabolic syndrome rises by approximately 5% in men and 9% in female with each 1 mg/dL increase in serum uric acid concentration. 356 Elevated serum uric acid levels have been shown to impair insulin sensitivity, thereby contributing to the development of insulin resistance. In response to increased insulin resistance, the pancreas compensates by secreting higher levels of insulin, resulting in hyperinsulinemia. 357 The prevalence of metabolic syndrome components, including hyperglycemia, hypertriglyceridemia, low HDL cholesterol, and hypertension, shows a rising trend with increasing serum uric acid levels. Interestingly, central obesity appeared to decrease slightly in individuals with exceptionally high serum uric acid concentrations. 200 Uric acid is implicated in the pathogenesis of metabolic syndrome through its ability to induce insulin resistance and promote low-grade inflammation, underscoring its proinflammatory role. 51 In addition, hyperuricemia is frequently accompanied by dyslipidemia, another hallmark of metabolic syndrome. Studies have demonstrated an association between elevated serum uric acid levels and alterations in lipid profiles, including increased triglycerides and decreased high-density lipoprotein cholesterol (HDL-C) levels. 358 These lipid abnormalities contribute to the dyslipidemia pattern often observed in individuals with metabolic syndrome. There is evidence to suggest that hyperuricemia may promote weight gain and central obesity, both of which are integral components of metabolic syndrome. Uric acid has been shown to influence adipogenesis and fat accumulation, potentially exacerbating obesity in individuals with MetS. 200

Hypertension and its mechanism

Hyperuricemia may acutely influence blood pressure through a renin-dependent pathophysiological mechanism. Additionally, it is postulated that hyperuricemia exacerbates hypertension by promoting systemic endothelial dysfunction and oxidative stress. 201 Epidemiological studies consistently demonstrate a robust association between hyperuricemia and the incidence of hypertension. Each 1 mg/dL rise in serum uric acid is linked to a 13–15% increase in hypertension risk. 299 Elevated serum uric acid levels constitute a substantial risk factor for both the onset and progression of hypertension. The precise mechanisms by which elevated uric acid concentrations lead to hypertension are not entirely understood but likely involve complex processes related to cardiovascular disease pathogenesis. The increase in blood pressure in hyperuricemic individuals is predominantly attributed to oxidative stress and intracellular urate activity, mediated chiefly by xanthine oxidoreductase (XOR). 299 Uric acid deposition-induced inflammation, resulting in endothelial dysfunction and vascular damage (referred to as vascular gout), can occur at serum uric acid levels exceeding 6.5 mg/dL. This threshold is notably higher than those typically linked with hypertension and cardiovascular disease. 201 Uric acid-lowering therapy effectively reduces both systolic and diastolic blood pressure in pediatric and adolescent patients newly diagnosed with essential hypertension, particularly in young individuals with a short duration of hypertension and preserved renal function. 200

Intervertebral degeneration (IVD) and its mechanism

Several studies have confirmed that the oxidative properties of physiological levels of UA can eliminate 60% of ROS in the body. 359 This reduction in ROS can inhibit autophagy in IVDs and reduce the apoptosis of myeloid cells caused by oxidative stress, maintaining the stability of the structure of IVD. 94 However, high concentrations of UA can promote oxidative stress and mitochondrial dysfunction. The induction of XO can promote the production of ROS, thus promoting oxidative stress in IVD and exacerbating IDD. Moreover, high osmolality induced by high uric acid levels may inhibit PDGF- and IGF-I-mediated DNA synthesis in the medulla oblongata. 268 Additionally, MSU crystals may accumulate in IVD under high uric acid conditions and cause damage to cone endplates. 360 MSU crystals cause cellular damage and mediate inflammatory responses, such as prostaglandin, bradykinin, IL-1, IL-6, and TNF-a. 337 The accumulation of inflammation and bone destruction affect the ability of cartilage endplates to provide nutrients to IVD, exacerbating IDD. 361

Therapy approaches for hyperuricemia

Hyperuricemia can manifest either asymptomatically or symptomatically, leading to distinct management approaches. 95 Thus, the management strategies for hyperuricemia typically involve two primary modalities: non-pharmacological interventions and pharmacological therapy. These approaches are tailored based on the clinical presentation and individual patient factors, aiming to mitigate the risk of complications. 362

Treatment of asymptomatic hyperuricemia

Non-pharmacological interventions play a crucial role in managing hyperuricemia, particularly in asymptomatic individuals. 363 , 364 Dietary modifications, such as adherence to a low-purine diet and avoidance of alcohol, particularly beer and spirits, sugar-sweetened beverages, heavy meals, and excessive intake of meat and seafood, have demonstrated efficacy in reducing uric acid levels by approximately 10-15%. 365 Furthermore, incorporating cherries, coffee, and low-fat dairy products into the diet can confer beneficial effects. Consumption of fructose-rich beverages should be minimized. Protein-rich vegetables like nuts, legumes, beans, spinach, cauliflower, and mushrooms can be consumed in moderation due to their low bioavailability of urate and high fiber content, which are less likely to elevate serum uric acid levels. 324 , 366 – 369 However, complete prohibition of purine intake is not recommended due to its limited effect on serum uric acid levels (approximately 1 mg/dL) and the significant burden it imposes on patients. 1 Instead, supplementation with vitamins such as ascorbic acid (vitamin C) and folic acid can help lower serum urate concentrations. Vitamin C, administered in doses ranging from 500 to 1000 mg/day, exhibits mild uricosuric properties and can complement dietary and lifestyle modifications. Similarly, folic acid supplementation has been shown to effectively reduce serum urate levels. 9 , 127 , 370 , 371 Of note, non-pharmacological interventions represent valuable adjunctive measures for all individuals with gout, encompassing weight management and avoidance of excessive consumption of purine-rich foods, alcoholic beverages, and fructose-rich beverages. However, complete elimination of purine intake is not recommended due to its limited impact on serum uric acid levels, typically resulting in a reduction of approximately 1 mg/dL. Nonetheless, exceptional cases may require pharmacotherapy even in asymptomatic individuals with elevated serum uric acid levels. 372 For instance, patients undergoing radiotherapy or chemotherapy for malignancies are at risk of uric acid nephropathy and may require preventive therapy with intravenous hydration and xanthine oxidase inhibitors. 330 , 373 , 374 Xanthine oxidase inhibitors are typically used in such case. In Japan, treatment of asymptomatic hyperuricemia is recommended to mitigate the risk of chronic diseases such as hypertension, coronary artery disease (CAD), and chronic kidney disease (CKD). 191 However, the decision to initiate pharmacotherapy for asymptomatic hyperuricemia remains debatable and should be based on individual risk factors and considerations. While recent studies suggest a potential association among hyperuricemia, cardiovascular and renal diseases, further research is needed to elucidate the mechanisms and clinical benefits of urate-lowering therapy in these populations. 102 , 320 , 375

Treatment of hyperuricemia with commodities

An analysis of twenty-two guidance documents revealed a consensus on target serum uric acid levels for long-term control, with 6.0 mg/dL (or 360 μmol/L) as the predominant recommendation. 362 Uric acid-lowering drugs can be broadly classified into three major groups: drugs that reduce uric acid synthesis (xanthine oxidase inhibitors), drugs that promote uric acid excretion (reabsorption inhibitors), and drugs that regulate uric acid metabolic hydrolysis (uricase inhibitors). 1 Irrespective of the specific urate-lowering therapy (ULT) selected, fundamental principles entail commencing treatment concurrently with prophylaxis and initiating with a conservative dosage, followed by systematic monitoring of serum uric acid levels and subsequent dose adjustment until the therapeutic target is attained. 310 For symptomatic hyperuricemia, the common pharmacological interventions for urate-lowering therapy (ULT) are illustrated in Fig. ​ Fig.4. 4 . Xanthine oxidase (XO) plays a central role in purine metabolism by catalyzing the conversion of hypoxanthine to xanthine and further to uric acid (UA). Concurrently, XO contributes to the production of reactive oxygen species (ROS). 372 Allopurinol, categorized as a purine-like XO inhibitor, and febuxostat and topiroxostat, classified as non-purine XO inhibitors, constitute the primary pharmacological approach for ULT. 326 , 376 , 377 By inhibiting XO activity, these agents demonstrate antioxidant properties by reducing ROS production associated with purine metabolism as well as remain the cornerstone of hyperuricemia treatment. 139 Uricosuric agents represent a secondary or alternative therapeutic option, with recent guidelines advocating their use in combination with XO inhibitors when monotherapy proves ineffective. 378 However, it is crucial to acknowledge that the predominant cause of hyperuricemia in most patients which is impaired renal clearance of uric acid. This impairment may be influenced by inherited renal transport factors or a reduced estimated glomerular filtration rate (eGFR). 102 , 189 , 320 , 330 In patients with lower eGFR levels, uricosuric agents may not be as effective, necessitating the use of alternative agents with different mechanisms of action. 379 – 381 Benzbromarone, another potent uricosuric drug, acts by inhibiting URAT1 and GLUT9. 328 , 382 Emerging evidence linking hyperuricemia to cardiovascular and metabolic comorbidities has spurred the development of novel agents. Lesinurad and arhalofenate, inhibitors of URAT1 and OAT4, respectively, offer promising therapeutic avenues. 383 , 384 Dotinurad, a selective urate reabsorption inhibitor available in Japan, inhibits URAT1 with high selectivity, demonstrating non-inferiority to febuxostat in lowering serum UA levels with no significant safety concerns 385 (Table ​ (Table4 4 ).

Update on the therapies for the treatment of hyperuricemia

Xanthine oxidase inhibitors (XOIs)

Xanthine oxidase catalyzes the conversion of purine metabolites to uric acid (UA). Therefore, xanthine oxidase inhibitors reduce UA production from both endogenous and dietary purine sources, making them the first-line therapies for managing hyperuricemia. 23 , 55

Allopurinol

Allopurinol is an inhibitory agent that interferes with xanthine oxidase-mediated purine synthesis; allopurinol undergoes metabolic conversion to alloxanthine, which is a potent xanthine oxidase enzyme inhibitor. 386 The dual action of allopurinol and its metabolite, alloxanthine, inhibits xanthine oxidase, effectively catalyzing the conversion of hypoxanthine to xanthine and its subsequent conversion to uric acid. Allopurinol is crucial for promoting the secondary utilization of hypoxanthine and xanthine through a metabolic pathway intricately linked with hypoxanthine-guanine phosphoribosyl transferase. This metabolic cascade contributes to the synthesis of nucleic acids and nucleotides, elucidating the multifaceted impact of allopurinol on purine metabolism. 358 This metabolic process results in an increased concentration of nucleotides, triggering feedback mechanisms that suppress the synthesis of purines. Consequently, the reduced levels of uric acid in both urine and serum contribute to a reduction in the occurrence of hyperuricemia. 383 The initial dose of 50 mg was given 1 ~ 2 times a day, and each time, the dose was increased by 50 ~ 100 mg. The general dose was 200 ~ 300 mg/d, divided into 2 ~ 3 doses, for a maximum daily dose of 600 mg. 387 Notably, the CKD-FIX study and the PERL trials demonstrated that allopurinol did not significantly slow the deterioration of estimated glomerular filtration rate (eGFR) in chronic kidney disease patients compared to placebo, over a span of 2 and 3 years, respectively. 388 , 389 However, a contrasting outcome was observed in a pediatric study where allopurinol treatment over four months led to an improvement in renal function in children with CKD. 390 The ALL-HEART trial, which included patients over the age of 60 with ischemic heart disease but without a history of gout, found that allopurinol did not reduce the incidence of non-fatal myocardial infarction, non-fatal stroke, or cardiovascular death over an average follow-up period of 4.8 years when compared to standard care. 391 Conversely, a smaller study involving 82 heart failure patients indicated that long-term allopurinol administration was associated with an improvement in left ventricular function. 392 However, an algorithm was developed to theoretically mitigate the risk of allopurinol hypersensitivity syndrome (AHS), which occurs in 2–8% of patients. 393 Allopurinol can cause severe cutaneous adverse reactions (SCARs), which is a primary concern associated with allopurinol use. SCARs are strongly correlated with the HLA B*5801 allele and include drug rash accompanied by eosinophilia and systemic symptoms, Stevens–Johnson syndrome, and toxic epidermal necrosis. 394 In certain regions, a precautionary measure involves tailoring the allopurinol dosage based on creatinine clearance, aiming to mitigate the risk associated with SCARs, particularly considering renal failure as a predisposing factor for these adverse reactions. Notably, when allopurinol doses are less than 300 mg daily, less than half of patients achieve the therapeutic target of a serum uric acid (SU) concentration less than 6.0 mg/dL. 395 Intriguingly, even in instances where allopurinol is not adjusted according to the estimated glomerular filtration rate (eGFR), approximately one-third of patients fail to attain SU levels below the designated threshold of 6.0 mg/dL. Nonetheless, a significant portion of patients receiving allopurinol fail to reach the target serum urate concentrations. 396 Notably, the ABCG2 Arg141Lys variant has been consistently linked with poor response to allopurinol across multiple independent cohorts. 397

Febuxostat, a nonpurine xanthine oxidase inhibitor, effectively reduces serum uric acid levels without impeding the enzymes involved in pyrimidine and purine metabolism and synthesis. Its biotransformation is facilitated by uridine diphosphate glucuronosyltransferase (UGT) enzymes. Notably, patients treated with febuxostat demonstrate a slightly reduced risk of heart failure exacerbation compared to those receiving allopurinol. 398 In China, febuxostat is recommended as a urate-lowering therapy and is prescribed at a daily dosage of 20–40 mg, contrasting with the global recommendation of 80-120 mg/day. In the United States, febuxostat is tolerated at doses of 40 and 80 mg per day, while in Europe it is 120 mg per day, and in Japan it is 10–60 mg per day. 336 The CONFIRMS trial provided evidence that a daily dosage of 80 mg of febuxostat is more efficacious in lowering serum uric acid levels than a 300 mg daily dose of allopurinol. 399 This nonpurine xanthine oxidase inhibitor is considered a viable alternative for individuals with allopurinol allergies. Notably, in scenarios of renal impairment, febuxostat is deemed more potent than allopurinol. 326 Approximately 65% of patients achieved serum uric acid levels less than 6.0 mg/dL, although concerns have been raised regarding the cardiac safety profile of febuxostat. 400 Common side effects of febuxostat encompass muscle pain, gastrointestinal discomfort, skin rashes, diarrhea, and a slight elevation in liver enzymes. Notably, the incidence of skin rashes is comparable to that observed with allopurinol. The manufacturer advises careful monitoring of liver function at the commencement of therapy and in the presence of any symptom’s indicative of liver injury. Importantly, the incidence of adverse effects associated with febuxostat remains low unless the daily dosage exceeds 120 mg. 376 In the PRIZE trial, a cohort of 483 individuals with asymptomatic hyperuricemia was randomly assigned to either a two-year treatment with febuxostat or a control group that received lifestyle modifications. The study found that febuxostat did not correlate with a slowed progression of carotid intima-media thickness. 401 However, a detailed sub-analysis revealed that the febuxostat group experienced a greater reduction in arterial stiffness parameters compared to the control group. 402 Additionally, another sub-analysis indicated that patients on febuxostat treatment exhibited improved diastolic function. 403 The FREED trial, involving 1070 elderly patients with hyperuricemia and cardiovascular risk factors, randomized participants to receive either febuxostat or non-febuxostat treatment. The results demonstrated that febuxostat was linked to a significantly reduced risk of the primary composite endpoint, encompassing cerebral, cardiovascular, renal events, and all-cause mortality. 404

Topiroxostat

Topiroxostat, a nonpurine xanthine oxidase inhibitor, interacts with multiple amino acid residues within the solvent channel and forms covalent bonds with the molybdenum ion. This interaction produces a hydroxylated 2-pyridine metabolite that effectively inhibits xanthine oxidase, a critical enzyme in uric acid metabolism. Additionally, topiroxostat inhibits the ATP-binding cassette transporter G2 (ABCG2), which plays a key role in renal uric acid reabsorption and the secretion of uric acid from the intestines. 394 However, topiroxostat has not received approval for use in the United States and Europe, although it is utilized in Japan. The medication is available in oral tablets of 20, 40, and 60 mg. The standard recommendation is to initiate treatment with a 20 mg dose administered twice daily, with a maximum approved dosage of 80 mg twice daily. 387 The literature on topiroxostat reports certain adverse effects, including polyarthritis, nasopharyngitis, and an increase in liver enzymes. Notably, the majority of these adverse effects are generally classified as mild to moderate in severity. 377 A study demonstrated a marked enhancement (≥150%) of warfarin activity in 32% of patients with cardiovascular disease and hyperuricemia who were treated with topiroxostat. 405 A prospective, randomized, blinded study compared the effects of topiroxostat with allopurinol and suggested that topiroxostat may lead to a reduction in left ventricular end-diastolic pressure, indicating a potential benefit for cardiac function. 406 Additionally, the study hinted at nephroprotective properties of topiroxostat compared to allopurinol. As for nephroprotection, an RCT on the use of febuxostat vs topiroxostat show none improvement in urinary protein/creatinine ratio. 407

Advanced therapy

Hyperuricemia can arise due to either overproduction or underexcretion of uric acid, with the latter being the predominant form as mentioned. The underexcretion of uric acid is primarily attributed to diminished renal clearance. 138 , 139 During renal filtration, uric acid is extensively handled by proximal tubular cells. Approximately 90% of the filtered uric acid is reabsorbed via the apical transporters URAT1 and OAT4, as well as the basolateral GLUT9. Conversely, a portion of uric acid is secreted back into the proximal tubular lumen through various apical transporters, including ABCG2, NPT1, NPT4, and GLUT9, along with the basolateral transporters OAT1 and OAT3. 138 , 139 Uricosuric agents act on the proximal tubule of the kidney by inhibiting the reabsorption of uric acid or enhancing its excretion. These medications are considered second-line treatments for hyperuricemia, particularly in cases unresponsive to standard therapies. They are often used in conjunction with xanthine oxidase (XO) inhibitors or prescribed for patients who cannot tolerate XO inhibitors. Additionally, certain antihypertensive and lipid-lowering drugs, such as losartan, simvastatin, atorvastatin, and fenofibrate, have been shown to reduce serum uric acid levels, potentially exhibiting a synergistic effect when used alongside standard hypouricemic treatments. 81 , 408

Probenecid is a quintessential uricosuric agent with multifaceted effects on renal function, significantly influencing the elimination of organic anions and tubular reabsorption of urate. Its therapeutic potential extends beyond managing hyperuricemia, demonstrating efficacy as a URAT1 and GLUT9 inhibitor, especially in cases of renal impairment. Probenecid exerts its uricosuric effects by inhibiting renal organic anion elimination and disrupting tubular urate reabsorption. This dual action enhances urinary uric acid excretion, thereby reducing serum urate concentrations. Additionally, probenecid may modulate urate binding by plasma proteins and influence uric acid secretion within the renal tubules. 397 The comprehensive use of probenecid is not without consideration of adverse reactions, as it spans various organ systems. Gastrointestinal, dermatologic, hematologic, renal, and immunologic manifestations have been reported. 409 Approximately 5% of users experience manifestations such as rash, gastrointestinal complaints, and hypersensitivity reactions. While serious toxicity is infrequently reported, a notable proportion of patients, approximately one-third, may exhibit intolerance, necessitating discontinuation of probenecid. 410

Benzbromarone

Benzbromarone, recognized as a uricosuric agent, exhibits notable in vitro inhibitory effects on urate transport facilitated by URAT1 and GLUT-9. Its approval for clinical use comes with cautious considerations, particularly in terms of dosing and associated hepatotoxicity. The recommended starting dosages of benzbromarone range from 12.5 mg to 50 mg daily, a regimen predominantly observed in Europe and Asia. 79 , 83 , 411 As novel URAT1 inhibitor uricosuric therapies gain momentum in clinical trials, particularly among Western populations, the application of benzbromarone warrants meticulous consideration. Patient selection for clinical trials should reflect the pathophysiologic subtype of hyperuricemia, existing comorbidities, and concurrent use of urine alkalization agents such as potassium citrate. This comprehensive approach facilitates a thorough evaluation of benzbromarone’s efficacy and safety across diverse patient cohorts, ultimately refining uricosuric therapy regimens. 55 The risk of hepatotoxicity is especially increased in individuals administered high doses of 300 mg daily of benzbromarone. However, findings from a comprehensive systematic review indicates that, when juxtaposed with probenecid, benzbromarone is associated with a reduced frequency of adverse effects. 378 Certain scholars posit that the removal of benzbromarone from the market may not align with the best interests of patients with gout, with the argument that conceivable toxicity could be mitigated through a cautious approach involving gradual dosage escalation coupled with vigilant monitoring of liver function. 327 Importantly, similar to those treated with febuxostat, patients on benzbromarone exhibited a significantly reduced risk of advancing to end-stage renal disease. 412 In an additional study, benzbromarone demonstrated a lower risk of experiencing the initial gout flare and developing type 2 diabetes when contrasted with allopurinol. 413 A randomized, open-label, crossover study comparing benzbromarone and febuxostat in hyperuricemia patients indicated that benzbromarone was associated with diminished endothelial dysfunction and an increase in adiponectin levels. 414

Emerging drugs and uricosuric compounds

Given the advancements in drug delivery systems and a deeper understanding of renal mechanisms and urate transporters, numerous novel therapeutic agents for managing hyperuricemia are currently in various stages of clinical development. 372 , 415 , 416 Emerging pharmacological agents for hyperuricemia management are currently undergoing various stages of clinical development, ranging from preclinical to early clinical trials. Notable candidates in Phase II/III trials include arhalofenate (MBX102), AC201, the RDEA group (including lesinurad), tranilast, and ulodesine (BCX4208). Additionally, Phase I trials are evaluating drugs such as levotofisopam and Marine Active. The primary goal of these innovative therapies is to improve serum uric acid control in patients with symptomatic hyperuricemia, particularly those with comorbid conditions. These new agents aim to offer enhanced tolerability and minimize adverse events compared to traditional treatments. However, it is important to acknowledge that uricosuric agents and emerging therapies that increase renal clearance of uric acid may also raise the risk of renal adverse events. 188

Lesinurad (RDEA594)

Lesinurad is a common URAT1 inhibitor that influences the serum uric acid concentration through the inhibition of URAT1 and OAT4. 394 Lesinurad is metabolized and eliminated predominantly by the liver (75%) and to a lesser extent by the kidneys (25%), with a half-life of approximately 9 to 10 h. The primary treatment-emergent adverse events reported with its use include serious cardiovascular events and potential nephrotoxicity. Nonetheless, clinical studies have demonstrated that lesinurad at a dosage of 200 mg once daily does not elevate the risk of renal, cardiovascular, or other adverse events beyond those associated with xanthine oxidase (XO) inhibitors alone, with the exception of transient increases in serum creatinine levels. 417 Nephrotoxicity emerges as the primary adverse effect associated with lesinurad, with its incidence being dose dependent. A recent Phase III clinical trial focused on gout patients who were intolerant or contraindicated to xanthine oxidase inhibitors (XOIs) revealed that lesinurad monotherapy at a dosage of 400 mg led to a significant incidence of elevated serum creatinine. Additionally, the trial reported renal-related adverse events, including serious adverse events, at a higher rate compared to the placebo group. 383 However, Lesinurad is a relatively new pharmaceutical agent, currently lacks data regarding its potential impact on cardiovascular and renal outcomes.

Arhalofenate (MBX-102)

Arhalofenate (MBX-102) is a uricosuric compound that has been investigated for its potential in the treatment of gout and hyperuricemia. It acts as a dual-acting agent, combining the properties of a uricosuric and a nonsteroidal anti-inflammatory drug (NSAID). By inhibiting URAT1, arhalofenate promotes the excretion of uric acid in the urine, reducing serum uric acid levels. 384 Furthermore, arhalofenate has anti-inflammatory properties, which can be beneficial in the context of gout, where inflammation plays a significant role in joint symptoms. However, clinical trials of arhalofenate have been conducted to assess its efficacy and safety in the treatment of gout and hyperuricemia. These trials aimed to evaluate its ability to lower serum uric acid levels, reduce gout flares, and provide anti-inflammatory effects. 418 Arhalofenate is available for oral administration in daily dosages are 200, 400, or 600 mg once. The U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) respectively concurred with a pharmaceutical company on the efficacy endpoints for two distinct clinical indications of arhalofenate in 2017. Currently, three Phase III trials are in progress, designed to assess the comparative efficacy of a combination therapy consisting of arhalofenate plus febuxostat 40 mg versus febuxostat monotherapy at 80 mg. These trials aim to evaluate the reduction in serum uric acid levels and the incidence of gout flares. 419

Dotinurad represents a novel and selective urate reabsorption inhibitor that has received approval for clinical application in Japan. This medication potently inhibits the URAT1 transporter to a lesser extent, which also affects ABCG2, OAT1, and OAT3. 420 Phase III clinical trials have substantiated the non-inferiority of dotinurad in comparison to both febuxostat and benzbromaron. 421 Notably, dotinurad has demonstrated safety in patients with an estimated glomerular filtration rate (eGFR) between 60 ml/min and 30 ml/min, without necessitating any dosage adjustments. In terms of adverse drug reactions, aggregated data from phase II and III studies indicate that while dotinurad can potentially cause liver-related adverse reactions, such as hepatic steatosis and abnormal liver function tests, which the incidence is lower compared to benzbromarone. 420

Tranilast, is recognized as an anti-inflammatory agent initially designed for treating allergic conditions such as asthma and allergic rhinitist. 422 – 424 Recent research has shed light on its efficacy in lowering urate levels by inhibiting renal transporters URAT1 and Glucose Transporter 9 (GLUT9). 425 In two separate preclinical trials, tranilast exhibited promising urate-lowering effects along with a reduction in inflammation associated with urate crystal deposition. Following the administration of a single dose of tranilast, a mean reduction in serum uric acid levels of 0.17 mg/dL at 4 h and 0.24 mg/dL at 24 h was observed. Headache was notably identified as the predominant adverse effect associated with tranilast. Furthermore, tranilast has been investigated in Phase II clinical trials in combination with allopurinol for patients experiencing moderate-to-severe gouty arthritis. 418

Ulodesine (BCX4208)

Ulodesine, an inhibitor of purine nucleoside phosphorylase (PNP), operates upstream of xanthine oxidase (XO) in the purine metabolism pathway. By blocking PNP activity, ulodesine diminishes the substrates available for XO, thereby reducing uric acid production. 426 Currently, this drug is in development for managing hyperuricemia in chronic gout. Promising results have been observed in two Phase II clinical trials, evaluating ulodesine both as a monotherapy and in combination with allopurinol. In a 24-week extension study, the treatment response rates for 5 mg, 10 mg, and 20 mg doses were 40%, 50%, and 45%, respectively, compared to a 25% response rate for the placebo. 427 , 428 Interestingly, no significant adverse events were documented compared to the placebo group. Ulodesine displays no interactions with CYP450 isoforms and undergoes no hepatic metabolism, thereby minimizing anticipated drug interactions. However, there are concerns regarding its potential effects on T cells. Deficiency of purine nucleoside phosphorylase (PNP) has been linked to immunodeficiency and autoimmune disorders. 243

Uricase, facilitating enhanced uric acid excretion involves the administration of exogenous urate oxidase, is an enzyme which not endogenously expressed in humans. Uricases are employed in the treatment of refractory gout and are capable of achieving a rapid reduction in hyperuricemia, significant resolution of tophi, alleviation of chronic joint pain, and enhancement of overall quality of life. 387 Urate oxidase catalyzes the breakdown of uric acid into 5-hydroxyisourate, which subsequently undergoes spontaneous degradation to allantoin without enzymatic assistance. The heightened solubility of allantoin, surpassing that of uric acid by 5-10-fold, facilitates its more efficient renal excretion. 429 Addressing this constraint, the development of a recombinant urate oxidase, rasburicase and pegloticase has shown superior efficacy in rapidly reducing uric acid plasma concentrations compared to allopurinol. 387 Pegloticase, a recombinant urate oxidase conjugated to polyethylene glycol (PEG), has been introduced to reduce immunogenicity and extend the half-life of rasburicase. Nevertheless, recent concerns regarding the development of antibodies against PEG in healthy blood donors prompt further exploration of potential implications for the efficacy of PEGylated pharmaceuticals. However, the main side effects include serious cardiovascular events and infusion reactions. 1 Rasburicase is approved for managing hyperuricemia linked to chemotherapy in cancer patients. It is known for its immunogenicity and infusion-related reactions, like pegloticase. Unlike pegloticase, however, rasburicase is not PEGylated and has a shorter half-life of 8 hours. 430 Rasburicase is predominantly employed in the management of tumor lysis syndrome owing to its rapid onset of action and short treatment duration. However, it is associated with significant incidences of infusion reactions, anaphylaxis, methemoglobinemia, and hemolysis, particularly in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. 431 However, the application of uricases has been constrained by factors such as availability, cost, and immunogenicity. Despite these limitations, uricases have the potential to become a primary therapeutic option for severe and challenging cases of hyperuricemia. They may be utilized as induction or debulking therapy to lower the urate pool, followed by maintenance with urate-lowering therapy (ULT).

Therapy frame and future considerations

Per the 2020 American College of Rheumatology guidelines, allopurinol is recommended as the initial therapeutic approach for symptomatic hyperuricemia, aiming to achieve a target serum uric acid level below 6 mg/dl. 432 Epidemiological studies suggest that maintaining a serum uric acid level below 5.5 mg/dl may offer enhanced cardiovascular and renal protection compared to target levels of 6 mg/dl or higher. 433 Maintaining urate levels at or below 360 μmol/L through urate-lowering therapy is deemed safe and crucial for the prevention and reversal of joint, cardiovascular and renal damages. 308 , 362 , 363 , 372 , 434 – 436 Additionally, EULAR guidelines recommend losartan for patients with hypertension and fenofibrate for those with hyperlipidemia, both of which have mild uricosuric effects. 336 , 437 Additionally, the British Society for Rheumatology advocates for a lower target serum uric acid level of less than 5 mg/dl. 438 Similarly, the Japanese Society of Gout and Nucleic Acid Metabolism endorses allopurinol as the primary therapy for hyperuricemia, with a target serum uric acid level of less than 6 mg/dl. Furthermore, they suggest initiating treatment for hyperuricemia when the serum uric acid level exceeds 8 mg/dl with at least one complication, or above 9 mg/dl without any complications. 439 , 440 Concurrently, the development of novel uricosuric compounds aims to address resistant hyperuricemia while maintaining a favorable safety profile. The uricosuric agents targeting the URAT1 transporter, such as lesinurad and dotinurad, along with the formulation of oral combination therapies comprising xanthine oxidase inhibitors and uricosuric agents, is poised to improve the attainment of the target serum uric acid level of less than 6 mg/dL. 387 In conclusion, navigating the intricacies of hyperuricemia treatment requires a tailored approach. To mitigate acute arthritis attacks and associated complications, early initiation of pharmacotherapeutic interventions is advisable. The dynamic landscape, characterized by established agents and novel contenders, necessitates ongoing research to optimize therapeutic strategies, ensuring efficacy while mitigating potential risks. 441

Conclusion and perspective

Among the history of hyperuricemia development, uric acid accumulation in serum characterizes hyperuricemia, a condition with diverse physiological roles ranging from antioxidant processes, pro-oxidative activities, pro-inflammatory activities, nitric oxide regulation, anti-aging effects and innate immune response. 14 – 16 Understanding its multifaceted functions and mechanisms is crucial for deciphering its implications in health and disease. Furthermore, circulating urate levels are intricately regulated by the balance between urate production and excretion, and the kidney plays a pivotal role in maintaining this homeostasis. 186 , 187 Urate transporters contribute to this delicate equilibrium. Genetic factors, particularly variations in urate transporter genes, significantly influence individual susceptibility to hyperuricemia. 245 , 442 Altered urate transport mechanisms, both in the gastrointestinal tract and kidneys, are implicated in the pathogenesis of diseases associated with hyperuricemia.(Fig. ​ hyperuricemia.(Fig.4) 4 ) Future genome-wide association studies should aim to broaden their scope by encompassing diverse ethnic groups and varied patient populations. Furthermore, investigations into comorbidities linked with hyperuricemia need expansion to better elucidate the role of transporter gene mutations in disease pathogenesis. 303 , 443 In the meantime, by utilizing the results of GWAS studies, clinicians can identify individuals at risk for adverse drug reactions better, thereby improving safety and treatment compliance. 150 Furthermore, redefining hyperuricemia as a dynamic variable rather than a static biochemical parameter may offer novel perspectives on its role in disease progression. As our understanding advances, the intricate nature of hyperuricemia-related diseases necessitates ongoing exploration, emphasizing the importance of innovative personalized medicine approaches and a nuanced perspective to unravel these complexities. Dysmetabolic intestinal flora potentially contributes to gout-related metabolic and inflammatory symptoms by promoting Th17 infiltration. The identification of probiotic strains, such as DM9218, capable of lowering uric acid levels represents a novel therapeutic avenue. Currently, the modulation of intestinal microbiota through microecological therapies, including probiotics, prebiotics, and fecal microbiota transplantation, is a prominent area of clinical investigation for preventing and managing hyperuricemia and gout. These interventions aim to restore intestinal microecological balance, increasingly recognized as pivotal in the pathophysiology of these conditions. By targeting the gut microbiome, these therapies offer a novel and potentially effective strategy for mitigating the risks and progression of hyperuricemia and gout, thereby contributing to a more holistic and personalized treatment approach in clinical practice. 143 , 444 Furthermore, identifying the distinct phenotypes is crucial, as hyperuricemia stemming from increased XO activity may have a different correlation with cardiovascular disease compared to that caused by renal underexcretion. Moreover, patients with the underexcretion phenotype might respond more favorably to uricosuric agents than to XO inhibitors. We suspect that biases in patient population selection could account for the inconsistent findings regarding the cardio and nephroprotective effects of hypouricemic agents in clinical trials. Differentiating between gout and asymptomatic hyperuricemia can be challenging, as gouty nephropathy may occur even in the absence of clinically apparent gout or with serum uric acid levels below the solubility threshold. There is an urgent need for future studies to delineate the effects of different classes of hypouricemic drugs on each hyperuricemia phenotypes. 372

In addition, in terms of the major mechanism of hyperuricemia induced commodities, oxidative stress, inflammatory signaling pathway and immune response are involved in this process, which mainly lead to cell apoptosis and endothelial dysfunction. 105 , 270 , 287 (Fig. ​ (Fig.5) 5 ) While some associations have been observed, particularly with gout and renal diseases, evidence from Mendelian randomization studies did not consistently support a causal relationship between elevated serum urate levels and other metabolic or cardiovascular disorders. However, hyperuricemia plays a role in promoting inflammation, oxidative stress, and endothelial dysfunction underscores its potential contribution to disease pathogenesis. 249 , 445 – 449 Uric acid exerts multifaceted effects on endothelial function and vascular health through its interactions with NO, ROS, and inflammatory pathways, highlighting its potential role in the pathogenesis of cardiovascular diseases like atherosclerosis. 69 , 90 , 256 Targeting these pathways may offer therapeutic opportunities for mitigating the adverse vascular effects of hyperuricemia. However, the precise mechanisms by which NLRP3 is activated in response to monosodium urate crystals remain incompletely understood. 91 , 114 , 263 , 423 , 450 , 451 The caspase-1-independent pathways of IL-1 production, including the specific proteases involved and the stimuli for their activation, are still not well-defined. Clarifying the stages at which these pathways contribute to the inflammatory phenotype and identifying the cell types orchestrating this inflammasome-independent response are crucial areas for further investigation. 337 , 340 , 452 Moreover, a pivotal area of research concerns the mechanisms that precipitate gouty attacks in patients with sustained monosodium urate crystal deposits. It remains uncertain whether distinct initiation mechanisms trigger the inflammatory response by acting on priming signaling pathways, or if a reduction in the negative regulation of NLRP3 activation amplifies the inflammatory cascade. 15 , 453 , 454 Current therapeutic approaches for hyperuricemia focus on mitigating associated complications and reducing serum UA levels with non-pharmacological interventions include dietary modifications and some environment factors. 455 Besides, pharmacological interventions primarily involve urate-lowering drugs, uricosuric compounds and emerging agents. 55 Traditional XO inhibitors and newer uricosuric compounds provide additional options for personalized treatment approaches. Newer uricosuric compounds, such as probenecid, lesinurad and arhalofenate, target different aspects of uric acid metabolism, providing additional options for personalized treatment approaches. Compared with XOIs, uricase, rasburicase and pegloticase convert UA to allantoin in adults with gout resistant to conventional therapy. 429 Precision medicine guided by genetic insights holds promise for tailoring hyperuricemia management to individualized needs. 410 Efforts are underway to develop novel therapies addressing unmet needs, such as alternative agents for long-term management of hyperuricemia. 201 , 411 , 438 , 456 Integration of genetics into hyperuricemia research offers opportunities for advancing personalized medical approaches and improving patient outcomes. In the future, precision medicine, guided by genetic variants, represents a promising avenue for tailoring hyperuricemia management to individualized needs. Hyperuricemia continues to be inadequately managed, primarily due to factors such as ineffective dosing of urate-lowering therapy, patient noncompliance, and intolerance/adverse events associated with current treatment options. 23 , 321 , 325 , 415 , 455 These limitations highlight the urgent needs for the creation of alternative treatment options capable of safely and effectively reducing serum uric acid levels for the long-term management of hyperuricemia. Acknowledging the growing need for better control of hyperuricemia, considerable research has been dedicated to the discovery and development of innovative therapies designed to meet these clinical challenges.

Acknowledgements

This study was performed with the support of the National Natural Science Foundation of China (82002339, 81820108020), Shanghai Frontiers Science Center of Degeneration and Regeneration in Skeletal System (BJ1-9000-22-4002). BioRender ( https://www.biorender.com/ ) was used to create the Figs. ​ Figs.3 3 and ​ and5 5 .

Author contributions

L.D., Y.Z., H.L., and J.G. drafted and conceived the initial manuscript. J.G., C.Z. and Z.Z. provided the essential assistant for our final manuscript. L.D., H.L., J.G., Q.W., B.Y., L. X., Y.P. and Y.Z. drew the figures and arranged the tables, contributed to the review of the literature and preparation of the manuscript. All authors have read and approved the article.

Competing interests

The authors declare no competing interests.

These authors contributed equally: Lin Du, Yao Zong, Haorui Li.

Contributor Information

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