The prevention and treatment of Plasmodium vivax malaria

Exploring Subsite Selectivity within Plasmodium vivax N-Myristoyltransferase Using Pyrazole-Derived Inhibitors

N-myristoyltransferase (NMT) is a promising antimalarial drug target. Despite biochemical similarities between Plasmodium vivax and human NMTs, our recent research demonstrated that high selectivity is achievable. Herein, we report PvNMT-inhibiting compounds aimed at identifying novel mechanisms of selectivity. Various functional groups are appended to a pyrazole moiety in the inhibitor to target a pocket formed beneath the peptide binding cleft. The inhibitor core group polarity, lipophilicity, and size are also varied to probe the water structure near a channel. Selectivity index values range from 0.8 to 125.3. Cocrystal structures of two selective compounds, determined at 1.97 and 2.43 Å, show that extensions bind the targeted pocket but with different stabilities. A bulky naphthalene moiety introduced into the core binds next to instead of displacing protein-bound waters, causing a shift in the inhibitor position and expanding the binding site. Our structure-activity data provide a conceptual foundation for guiding future inhibitor optimizations.

Azithromycin disrupts apicoplast biogenesis in replicating and dormant liver stages of the relapsing malaria parasites Plasmodium vivax and Plasmodium cynomolgi

The control and elimination of malaria caused by Plasmodium vivax is hampered by the threat of relapsed infection resulting from the activation of dormant hepatic hypnozoites. Currently, only the 8-aminoquinolines, primaquine and tafenoquine, have been approved for the elimination of hypnozoites, although their use is hampered by potential toxicity. Therefore, an alternative radical curative drug that safely eliminates hypnozoites is a pressing need. This study assessed the potential hypnozoiticidal activity of the antibiotic azithromycin, which is thought to exert antimalarial activity by inhibiting prokaryote-like ribosomal translation within the apicoplast, an indispensable organelle. The results show that azithromycin inhibited apicoplast development during liver-stage schizogony in P. vivax and Plasmodium cynomolgi, leading to impaired parasite maturation. More importantly, this study found that azithromycin is likely to impair the hypnozoite's apicoplast, resulting in the loss of this organelle. Subsequently, using a recently developed long-term hepatocyte culture system, this study found that this loss likely induces a delay in the hypnozoite activation rate, and that those parasites that do proceed to schizogony display liver-stage arrest prior to differentiating into hepatic merozoites, thus potentially preventing relapse. Overall, this work provides evidence for the potential use of azithromycin for the radical cure of relapsing malaria, and identifies apicoplast functions as potential drug targets in quiescent hypnozoites.

A Systematic Literature Review of Mathematical Models for Coinfections: Tuberculosis, Malaria, and HIV/AIDS

Tuberculosis, malaria, and HIV are among the most lethal diseases, with AIDS (Acquired Immune Deficiency Syndrome) being a chronic and potentially life-threatening condition caused by the human immunodeficiency virus (HIV). Individually, each of these infections presents a significant health challenge. However, when tuberculosis, malaria, and HIV co-occur, the symptoms can worsen, leading to an increased mortality risk. Mathematical models have been created to study coinfections involving tuberculosis, malaria, and HIV. This systematic literature review explores the importance of coinfection models by examining articles from reputable databases such as Dimensions, ScienceDirect, Scopus, and PubMed. The primary emphasis is on investigating coinfection models related to tuberculosis, malaria, and HIV. The findings demonstrate that each article thoroughly covers various aspects, including model development, mathematical analysis, sensitivity analysis, optimal control strategies, and research discoveries. Based on our comprehensive evaluation, we offer valuable recommendations for future research efforts in this field.

Quantifying the impact of interventions against Plasmodium vivax: A model for country-specific use

In order to evaluate the impact of various intervention strategies on Plasmodium vivax dynamics in low endemicity settings without significant seasonal pattern, we introduce a simple mathematical model that can be easily adapted to reported case numbers similar to that collected by surveillance systems in various countries. The model includes case management, vector control, mass drug administration and reactive case detection interventions and is implemented in both deterministic and stochastic frameworks. It is available as an R package to enable users to calibrate and simulate it with their own data. Although we only illustrate its use on fictitious data, by simulating and comparing the impact of various intervention combinations on malaria risk and burden, this model could be a useful tool for strategic planning, implementation and resource mobilization.

In Vitro Antimalarial Activity of Trichothecenes against Liver and Blood Stages of Plasmodium Species

Trichothecenes (TCNs) are a large group of tricyclic sesquiterpenoid mycotoxins that have intriguing structural features and remarkable biological activities. Herein, we focused on three TCNs (anguidine, verrucarin A, and verrucarol) and their ability to target both the blood and liver stages of Plasmodium species, the parasite responsible for malaria. Anguidine and verrucarin A were found to be highly effective against the blood and liver stages of malaria, while verrucarol had no effect at the highest concentration tested. However, these compounds were also found to be cytotoxic and, thus, not selective, making them unsuitable for drug development. Nonetheless, they could be useful as chemical probes for protein synthesis inhibitors due to their direct impact on parasite synthesis processes.

Potent AMA1-specific human monoclonal antibody against P. vivax Pre-erythrocytic and Blood Stages

New therapeutics are a priority for preventing and eliminating Plasmodium vivax (Pv) malaria because of its easy transmissibility and dormant stages in the liver. Relapses due to the dormant liver stages are the major contributor to reoccurring Pv. Therefore, therapies that reduce the establishment of dormant parasites and blood-stage infection are important for controlling this geographically widespread parasite. Here, we isolated 12 human monoclonal antibodies (humAbs) from the plasma of a Pv-exposed individual that recognized Pv apical membrane antigen 1 (PvAMA1). PvAMA1 is important for both sporozoite invasion of hepatocytes and merozoite invasion of reticulocytes. We identified one humAb, 826827, that blocked invasion of human erythrocytes using a transgenic P. falciparum line expressing PvAMA1 (IC 50 = 3 µg/mL) and all Pv clinical isolates in vitro . This humAb also inhibited sporozoite invasion of a human hepatocyte cell line and primary human hepatocytes (IC 50 of 0.3 - 3.7 µg/mL). The crystal structure of recombinant PvAMA1 with the antigen-binding fragment of 826827 at 2.4 Å resolution shows that the humAb partially occupies the highly conserved hydrophobic groove in PvAMA1 that binds its known receptor, RON2. HumAb 826827 binds to PvAMA1 with higher affinity than RON2, accounting for its potency. To our knowledge, this is the first reported humAb specific to PvAMA1, and the PvAMA1 residues it binds to are highly conserved across different isolates, explaining its strain-transcendent properties.

Primaquine dose and the risk of haemolysis in patients with uncomplicated Plasmodium vivax malaria: a systematic review and individual patient data meta-analysis

BACKGROUND

Primaquine radical cure is used to treat dormant liver-stage parasites and prevent relapsing Plasmodium vivax malaria but is limited by concerns of haemolysis. We undertook a systematic review and individual patient data meta-analysis to investigate the haematological safety of different primaquine regimens for P vivax radical cure.

METHODS

For this systematic review and individual patient data meta-analysis, we searched MEDLINE, Web of Science, Embase, and Cochrane Central for prospective clinical studies of uncomplicated P vivax from endemic countries published between Jan 1, 2000, and June 8, 2023. We included studies if they had active follow-up of at least 28 days, if they included a treatment group with daily primaquine given over multiple days where primaquine was commenced within 3 days of schizontocidal treatment and was given alone or coadministered with chloroquine or one of four artemisinin-based combination therapies (ie, artemether-lumefantrine, artesunate-mefloquine, artesunate-amodiaquine, or dihydroartemisinin-piperaquine), and if they recorded haemoglobin or haematocrit concentrations on day 0. We excluded studies if they were on prevention, prophylaxis, or patients with severe malaria, or if data were extracted retrospectively from medical records outside of a planned trial. For the meta-analysis, we contacted the investigators of eligible trials to request individual patient data and we then pooled data that were made available by Aug 23, 2021. The main outcome was haemoglobin reduction of more than 25% to a concentration of less than 7 g/dL by day 14. Haemoglobin concentration changes between day 0 and days 2-3 and between day 0 and days 5-7 were assessed by mixed-effects linear regression for patients with glucose-6-phosphate dehydrogenase (G6PD) activity of (1) 30% or higher and (2) between 30% and less than 70%. The study was registered with PROSPERO, CRD42019154470 and CRD42022303680.

FINDINGS

Of 226 identified studies, 18 studies with patient-level data from 5462 patients from 15 countries were included in the analysis. A haemoglobin reduction of more than 25% to a concentration of less than 7 g/dL occurred in one (0·1%) of 1208 patients treated without primaquine, none of 893 patients treated with a low daily dose of primaquine (<0·375 mg/kg per day), five (0·3%) of 1464 patients treated with an intermediate daily dose (0·375 mg/kg per day to <0·75 mg/kg per day), and six (0·5%) of 1269 patients treated with a high daily dose (≥0·75 mg/kg per day). The covariate-adjusted mean estimated haemoglobin changes at days 2-3 were -0·6 g/dL (95% CI -0·7 to -0·5), -0·7 g/dL (-0·8 to -0·5), -0·6 g/dL (-0·7 to -0·4), and -0·5 g/dL (-0·7 to -0·4), respectively. In 51 patients with G6PD activity between 30% and less than 70%, the adjusted mean haemoglobin concentration on days 2-3 decreased as G6PD activity decreased; two patients in this group who were treated with a high daily dose of primaquine had a reduction of more than 25% to a concentration of less than 7 g/dL. 17 of 18 included studies had a low or unclear risk of bias.

INTERPRETATION

Treatment of patients with G6PD activity of 30% or higher with 0·25-0·5 mg/kg per day primaquine regimens and patients with G6PD activity of 70% or higher with 0·25-1 mg/kg per day regimens were associated with similar risks of haemolysis to those in patients treated without primaquine, supporting the safe use of primaquine radical cure at these doses.

FUNDING

Australian National Health and Medical Research Council, Bill & Melinda Gates Foundation, and Medicines for Malaria Venture.

Interventions for promoting patients' adherence to 14-day primaquine treatment in a highly malaria-endemic township in Myanmar: a qualitative study among key stakeholders

BACKGROUND

Plasmodium vivax malaria is considered a major threat to malaria eradication. The radical cure for P. vivax malaria normally requires a 14-day administration of primaquine (PQ) to clear hypnozoites. However, maintaining adherence to PQ treatment is a significant challenge, particularly in malaria-endemic rural areas. Hence, this study aimed to formulate interventions for promoting patients' commitment to PQ treatment in a highly malaria-endemic township in Myanmar.

METHODS

A qualitative study was conducted in Waingmaw Township in northern Myanmar, where P. vivax malaria is highly endemic. Key stakeholders including public health officers and community members participated in focus group discussions (FGDs) and in-depth interviews (IDIs) in September 2022. Data were collected using validated guidelines, translated into English, and visualized through thematic analysis.

RESULTS

Responsible individuals from different levels of the Myanmar National Malaria Control Programme participated in the IDIs. Most of them reported being aware of the markedly increasing trend of P. vivax and the possibility of relapse cases, especially among migrants who are lost to follow-up. Workload was a key concern surrounding intervention implementation. The respondents discussed possible interventions, such as implementing directly observed treatment (DOT) by family members, piloting a shorter PQ regimen, expanding the community's malaria volunteer network, and strengthening health education activities using local languages to promote reasonable drug adherence. FGDs among community members revealed that although people were knowledgeable about malaria symptoms, places to seek treatment, and the use of bed nets to prevent mosquito bites, most of them still preferred to be treated by quack doctors and rarely used insecticide-treated nets at worksites. Many often stopped taking the prescribed drugs once the symptoms disappeared. Nevertheless, some respondents requested more bed nets to be distributed and health promotion activities to be conducted.

CONCLUSION

In rural areas where human resources are limited, interventions such as implementing family member DOT or shortening PQ regimens should be introduced to enhance the radical cure for the P. vivax infection. Disseminating information about the importance of taking the entire treatment course and emphasizing the burden of relapse is also essential.

Interventions for promoting patients' adherence to 14-day primaquine treatment in a highly malaria-endemic township in Myanmar: A qualitative study among key stakeholders

Background

Plasmodium vivax malaria is considered a major threat to malaria eradication. The radical cure for P. vivax malaria normally requires a 14-day administration of primaquine (PQ) to clear hypnozoites. However, maintaining adherence to PQ treatment is a significant challenge, particularly in malaria-endemic rural areas. Hence, this study aimed to formulate interventions for promoting patients' commitment to PQ treatment in a highly malaria-endemic township in Myanmar.

Methods

A qualitative study was conducted in Waingmaw Township in northern Myanmar, where P. vivax malaria is highly endemic. Key stakeholders including public health officers and community members participated in focus group discussions (FGDs) and in-depth interviews (IDIs) in September 2022. Data were collected using validated guidelines, translated into English, and visualized through thematic analysis.

Results

Responsible individuals from different levels of the Myanmar National Malaria Control Program participated in the IDIs. Most of them reported being aware of the markedly increasing trend of P. vivax and the possibility of relapse cases, especially among migrants who are lost to follow-up. Workload was a key concern surrounding intervention implementation. The respondents discussed possible interventions, such as implementing directly observed treatment (DOT) by family members, piloting a shorter PQ regimen, expanding the community's malaria volunteer network, and strengthening health education activities using local languages to promote reasonable drug adherence. FGDs among community members revealed that although people were knowledgeable about malaria symptoms, places to seek treatment, and the use of bed nets to prevent mosquito bites, most of them still preferred to be treated by quack doctors and rarely used insecticide-treated nets at worksites. Many often stopped taking the prescribed drugs once the symptoms disappeared. Nevertheless, some respondents requested more bed nets to be distributed and health promotion activities to be conducted.

Conclusion

In rural areas where human resources are limited, interventions such as implementing family member DOT or shortening PQ regimens should be introduced to enhance the radical cure for the P. vivax infection. Disseminating information about the importance of taking the entire treatment course and emphasizing the burden of relapse is also essential.

Identification of potent and selective N-myristoyltransferase inhibitors of Plasmodium vivax liver stage hypnozoites and schizonts

Drugs targeting multiple stages of the Plasmodium vivax life cycle are needed to reduce the health and economic burdens caused by malaria worldwide. N-myristoyltransferase (NMT) is an essential eukaryotic enzyme and a validated drug target for combating malaria. However, previous PvNMT inhibitors have failed due to their low selectivity over human NMTs. Herein, we apply a structure-guided hybridization approach combining chemical moieties of previously reported NMT inhibitors to develop the next generation of PvNMT inhibitors. A high-resolution crystal structure of PvNMT bound to a representative selective hybrid compound reveals a unique binding site architecture that includes a selective conformation of a key tyrosine residue. The hybridized compounds significantly decrease P. falciparum blood-stage parasite load and consistently exhibit dose-dependent inhibition of P. vivax liver stage schizonts and hypnozoites. Our data demonstrate that hybridized NMT inhibitors can be multistage antimalarials, targeting dormant and developing forms of liver and blood stage.

Nationwide spatiotemporal drug resistance genetic profiling from over three decades in Indian Plasmodium falciparum and Plasmodium vivax isolates

BACKGROUND

Drug resistance is a serious impediment to efficient control and elimination of malaria in endemic areas.

METHODS

This study aimed at analysing the genetic profile of molecular drug resistance in Plasmodium falciparum and Plasmodium vivax parasites from India over a ~ 30-year period (1993-2019). Blood samples of P. falciparum and/or P. vivax-infected patients were collected from 14 regions across India. Plasmodial genome was extracted and used for PCR amplification and sequencing of drug resistance genes in P. falciparum (crt, dhps, dhfr, mdr1, k13) and P. vivax (crt-o, dhps, dhfr, mdr1, k12) field isolates.

RESULTS

The double mutant pfcrt SVMNT was highly predominant across the country over three decades, with restricted presence of triple mutant CVIET from Maharashtra in 2012. High rates of pfdhfr-pfdhps quadruple mutants were observed with marginal presence of "fully resistant" quintuple mutant ACIRNI-ISGEAA. Also, resistant pfdhfr and pfdhps haplotype has significantly increased in Delhi between 1994 and 2010. For pfmdr1, only 86Y and 184F mutations were present while no pfk13 mutations associated with artemisinin resistance were observed. Regarding P. vivax isolates, the pvcrt-o K10 "AAG" insertion was absent in all samples collected from Delhi in 2017. Pvdhps double mutant SGNAV was found only in Goa samples of year 2008 for the first time. The pvmdr1 908L, 958M and 1076L mutations were highly prevalent in Delhi and Haryana between 2015 and 2019 at complete fixation. One nonsynonymous novel pvk12 polymorphism was identified (K264R) in Goa.

CONCLUSIONS

These findings support continuous surveillance and characterization of P. falciparum and P. vivax populations as proxy for effectiveness of anti-malarial drugs in India, especially for independent emergence of artemisinin drug resistance as recently seen in Africa.

Expression, Purification, and Characterization of Plasmodium vivax Lactate Dehydrogenase from Bacteria without Codon Optimization

Plasmodium vivax is the most widespread cause of malaria, especially in subtropical and temperate regions such as Asia-Pacific and America. P. vivax lactate dehydrogenase (PvLDH), an essential enzyme in the glycolytic pathway, is required for the development and reproduction of the parasite. Thus, LDH from these parasites has garnered attention as a diagnostic biomarker for malaria and as a potential molecular target for developing antimalarial drugs. In this study, we prepared a transformed Escherichia coli strain for the overexpression of PvLDH without codon optimization. We introduced this recombinant plasmid DNA prepared by insertion of the PvLDH gene in the pET-21a(+) expression vector, into the Rosetta(DE3), an E. coli strain suitable for eukaryotic protein expression. The time, temperature, and inducer concentration for PvLDH expression from this E. coli Rosetta(DE3), containing the original PvLDH gene, were optimized. We obtained PvLDH with a 31.0 mg/L yield and high purity (>95%) from this Rosetta(DE3) strain. The purified protein was characterized structurally and functionally. The PvLDH expressed and purified from transformed bacteria without codon optimization was successfully demonstrated to exhibit its potential tetramer structure and enzyme activity. These findings are expected to provide valuable insights for research on infectious diseases, metabolism, diagnostics, and therapeutics for malaria caused by P. vivax.

Risk of hemolysis in Plasmodium vivax malaria patients receiving standard primaquine treatment in a population with high prevalence of G6PD deficiency

BACKGROUND

Primaquine is essential for the radical cure of Plasmodium vivax malaria, but it poses a potential danger of severe hemolysis in G6PD-deficient (G6PDd) patients. This study aimed to determine whether primaquine is safe in a population with high G6PD prevalence but lacking G6PD diagnosis capacity.

METHODS

In Myanmar, 152 vivax patients were gender- and age-matched at 1:3 for G6PDd versus G6PD-normal (G6PDn). Their risk of acute hemolysis was followed for 28 days after treatment with the standard chloroquine and 14-day primaquine (0.25 mg/kg/day) regimen.

RESULTS

Patients anemic and non-anemic at enrollment showed a rising and declining trend in the mean hemoglobin level, respectively. In males, the G6PDd group showed substantially larger magnitudes of hemoglobin reduction and lower hemoglobin nadir levels than the G6PDn group, but this trend was not evident in females. Almost 1/3 of the patients experienced clinically concerning declines in hemoglobin, with five requiring blood transfusion.

CONCLUSIONS

The standard 14-day primaquine regimen carries a significant risk of acute hemolytic anemia (AHA) in vivax patients without G6PD testing in a population with a high prevalence of G6PD deficiency and anemia. G6PD testing would avoid most of the clinically significant Hb reductions and AHA in male patients.

Population-based genomic study of Plasmodium vivax malaria in seven Brazilian states and across South America

Background

Brazil is a unique and understudied setting for malaria, with complex foci of transmission associated with human and environmental conditions. An understanding of the population genomic diversity of P. vivax parasites across Brazil can support malaria control strategies.

Methods

Through whole genome sequencing of P. vivax isolates across 7 Brazilian states, we use population genomic approaches to compare genetic diversity within country (n = 123), continent (6 countries, n = 315) and globally (26 countries, n = 885).

Findings

We confirm that South American isolates are distinct, have more ancestral populations than the other global regions, with differentiating mutations in genes under selective pressure linked to antimalarial drugs (pvmdr1, pvdhfr-ts) and mosquito vectors (pvcrmp3, pvP45/48, pvP47). We demonstrate Brazil as a distinct parasite population, with signals of selection including ABC transporter (PvABCI3) and PHIST exported proteins.

Interpretation

Brazil has a complex population structure, with evidence of P. simium infections and Amazonian parasites separating into multiple clusters. Overall, our work provides the first Brazil-wide analysis of P. vivax population structure and identifies important mutations, which can inform future research and control measures.

Funding

AI is funded by an MRC LiD PhD studentship. TGC is funded by the Medical Research Council (Grant no. MR/M01360X/1, MR/N010469/1, MR/R025576/1, MR/R020973/1 and MR/X005895/1). SC is funded by Medical Research Council UK grants (MR/M01360X/1, MR/R025576/1, MR/R020973/1 and MR/X005895/1) and Bloomsbury SET (ref. CCF17-7779). FN is funded by The Shloklo Malaria Research Unit - part of the Mahidol Oxford Research Unit, supported by the Wellcome Trust (Grant no. 220211). ARSB is funded by São Paulo Research Foundation - FAPESP (Grant no. 2002/09546-1). RLDM is funded by Brazilian National Council for Scientific and Technological Development - CNPq (Grant no. 302353/2003-8 and 471605/2011-5); CRFM is funded by FAPESP (Grant no. 2020/06747-4) and CNPq (Grant no. 302917/2019-5 and 408636/2018-1); JGD is funded by FAPESP fellowships (2016/13465-0 and 2019/12068-5) and CNPq (Grant no. 409216/2018-6).

In Vivo Antimalarial Activity of Trichosanthes cucumerina Against Plasmodium berghei NK65 in Mice

Undoubtedly, malaria is a vector-borne infectious disease that is increasingly being given attention by many researchers in their efforts to find the best drugs for its treatment. Four groups of mice (6-8 weeks old, 20-25 gram body weight (g bw) were inoculated with Plasmodium berghei NK65 intraperitoneally (i.p.) at 1.0 × 106 infected red blood cells (RBC) before being orally treated for the prophylactic and curative treatment regime with 0.2 mL of 100 mg/kg bw freeze-dried T. cucumerina aqueous extract. Parasitemia levels and inhibition rates were microscopically measured using Giemsa stained blood smear method. Trichosanthes cucumerina possessed strong antimalarial activities against P. berghei NK65 infection in mice. A significant correlation was successfully recorded between the survival time of the seven-day prophylactic treatment group (P7) with its ability to inhibit parasite growth as compared to the curative treatment groups. However, these values ​​are still incomparable to the control group treated with the commercial drugs primaquine and chloroquine. In addition, blood biochemical toxicity analysis of ALT, AST, ALP, and STP showed that acute and sub-acute toxicity treatments of T. cucumerina did not cause liver injury and were non-toxic to the animals. Thus, this study significantly proves (p≤0.05, n=6) that T. cucumerina has antiparasitic properties that can be manipulated as an alternative antimalarial drug.

Plasmodium vivax: the potential obstacles it presents to malaria elimination and eradication

Initiatives to eradicate malaria have a good impact on P. falciparum malaria worldwide. P. vivax, however, still presents significant difficulties. This is due to its unique biological traits, which, in comparison to P. falciparum, pose serious challenges for malaria elimination approaches. P. vivax's numerous distinctive characteristics and its ability to live for weeks to years in liver cells in its hypnozoite form, which may elude the human immune system and blood-stage therapy and offer protection during mosquito-free seasons. Many malaria patients are not fully treated because of contraindications to primaquine use in pregnant and nursing women and are still vulnerable to P. vivax relapses, although there are medications that could radical cure P. vivax. Additionally, due to CYP2D6's highly variable genetic polymorphism, the pharmacokinetics of primaquine may be impacted. Due to their inability to metabolize PQ, some CYP2D6 polymorphism alleles can cause patients to not respond to treatment. Tafenoquine offers a radical treatment in a single dose that overcomes the potentially serious problem of poor adherence to daily primaquine. Despite this benefit, hemolysis of the early erythrocytes continues in individuals with G6PD deficiency until all susceptible cells have been eliminated. Field techniques such as microscopy or rapid diagnostic tests (RDTs) miss the large number of submicroscopic and/or asymptomatic infections brought on by reticulocyte tropism and the low parasitemia levels that accompany it. Moreover, P. vivax gametocytes grow more quickly and are much more prevalent in the bloodstream. P. vivax populations also have a great deal of genetic variation throughout their genome, which ensures evolutionary fitness and boosts adaptation potential. Furthermore, P. vivax fully develops in the mosquito faster than P. falciparum. These characteristics contribute to parasite reservoirs in the human population and facilitate faster transmission. Overall, no genuine chance of eradication is predicted in the next few years unless new tools for lowering malaria transmission are developed (i.e., malaria elimination and eradication). The challenging characteristics of P. vivax that impede the elimination and eradication of malaria are thus discussed in this article.

Elucidating the status of malaria in Andaman and Nicobar Islands post-millennium 2000

Malaria is a major vector-borne disease in the Indian sub-continent and has been pestering Andaman and Nicobar islands (ANI's) as well since British colonial times. A retrospective data mining technique has been adhered to assess the status of malaria for nineteen years from 2000 to 2019 in ANI's. The altered environment due to 2004 tsunami had increased malaria incidence significantly during (2005-2010). The Nicobar district recorded high incidence of malaria while the least in the north and middle Andaman district. Comparative high incidence of malaria was documented due to Plasmodium falciparum than Plasmodium vivax in the Nicobar district between 2005 and 2009. The declining trend of malaria-positive cases in ANI's was observed post 2010, articulating various initiatives taken by the local Andaman and Nicobar administration to curb this vector-borne disease. The initiatives were like (1) large-scale release of larvivorous fish, Gambusia affinis in the transient water pools, (2) outdoor application of DDT, (3) indoor application of Pyrethrum, (4) malaria awareness drive that led to the curbing of the proliferation not only the malaria vector but also other potential mosquito vector species as well, and (5) implementation of revised drug policy.

Plasmodium cynomolgi in humans: current knowledge and future directions of an emerging zoonotic malaria parasite

Plasmodium cynomolgi (Pcy), a simian malaria parasite, is a recent perfect example of emerging zoonotic transfer in human. This review summarizes the current knowledge on the epidemiology of natural Pcy infections in humans, mosquitoes and monkeys, along with its biological, clinical and drug sensitivity patterns. Knowledge gaps and further studies on Pcy in humans are also discussed. This parasite currently seems to be geographically limited in South-East Asia (SEA) with a global prevalence in human ranging from 0 to 1.4%. The Pcy infections were reported in local SEA populations and European travelers, and range from asymptomatic carriage to mild/moderate attacks with no evidence of pathognomonic clinical and laboratory patterns but with Pcy strain-shaped clinical differences. Geographical distribution and competence of suitable mosquito vectors and non-primate hosts, globalization, climate change, and increased intrusion of humans into the habitat of monkeys are key determinants to emergence of Pcy parasites in humans, along with its expansion outside SEA. Sensitization/information campaigns coupled with training and assessment sessions of microscopists and clinicians on Pcy are greatly needed to improve data on the epidemiology and management of human Pcy infection. There is a need for development of sensitive and specific molecular tools for individual diagnosis and epidemiological studies. The development of safe and efficient anti-hypnozoite drugs is the main therapeutic challenge for controlling human relapsing malaria parasites. Experience gained from P. knowlesi malaria, development of integrated measures and strategies—ideally with components related to human, monkeys, mosquito vectors, and environment—could be very helpful to prevent emergence of Pcy malaria in humans through disruption of transmission chain from monkeys to humans and ultimately contain its expansion in SEA and potential outbreaks in a context of malaria elimination.

Fighting Plasmodium chloroquine resistance with acetylenic chloroquine analogues

Malaria is among the tropical diseases that cause the most deaths in Africa. Around 500,000 malaria deaths are reported yearly among African children under the age of five. Chloroquine (CQ) is a low-cost antimalarial used worldwide for the treatment of Plasmodium vivax malaria. Due to resistance mechanisms, CQ is no longer effective against most malaria cases caused by P. falciparum. The World Health Organization recommends artemisinin combination therapies for P. falciparum malaria, but resistance is emerging in Southeast Asia and some parts of Africa. Therefore, new medicines for treating malaria are urgently needed. Previously, our group identified the 4-aminoquinoline DAQ, a CQ analog containing an acetylenic bond in its side chain, which overcomes CQ resistance in K1 P. falciparum strains. In this work, the antiplasmodial profile, drug-like properties, and pharmacokinetics of DAQ were further investigated. DAQ showed no cross-resistance against standard CQ-resistant strains (e.g., Dd2, IPC 4912, RF12) nor against P. falciparum and P. vivax isolates from patients in the Brazilian Amazon. Using drug pressure assays, DAQ showed a low propensity to generate resistance. DAQ showed considerable solubility but low metabolic stability. The main metabolite was identified as a mono N-deethylated derivative (DAQ_M), which also showed significant inhibitory activity against CQ-resistant P. falciparum strains. Our findings indicated that the presence of a triple bond in CQ-analogues may represent a low-cost opportunity to overcome known mechanisms of resistance in the malaria parasite.

Update on pathogenesis, management, and control of Plasmodium vivax

PURPOSE OF REVIEW

This is a review of Plasmodium vivax epidemiology, pathogenesis, disease presentation, treatment and innovations in control and elimination. Here, we examine the recent literature and summarize new advances and ongoing challenges in the management of P. vivax .

RECENT FINDINGS

P. vivax has a complex life cycle in the human host which impacts disease severity and treatment regimens. There is increasing data for the presence of cryptic reservoirs in the spleen and bone marrow which may contribute to chronic vivax infections and possibly disease severity. Methods to map the geospatial epidemiology of P. vivax chloroquine resistance are advancing, and they will inform local treatment guidelines. P. vivax treatment requires an 8-aminoquinoline to eradicate the dormant liver stage. Evidence suggests that higher doses of 8-aminoquinolines may be needed for radical cure of tropical frequent-relapsing strains.

SUMMARY

P. vivax is a significant global health problem. There have been recent developments in understanding the complexity of P. vivax biology and optimization of antimalarial therapy. Studies toward the development of best practices for P. vivax control and elimination programs are ongoing.

Comparison of various RBC indices and Glucose 6 phosphate dehydrogenase activity in patients with and without malaria

Introduction and Aim: Malaria is endemic in many parts of India. Glucose 6 phosphate dehydrogenase (G6PD) deficiency is known to protect against malaria. G6PD deficient individuals afflicted with malaria when treated with primaquine, the first line oxidant drug of malaria, encounter adverse to fatal complications due to acute precipitation of hemolytic anemia. There is a need to assess RBC indices in malaria, its implications in G6PD deficiency, and its acute manifestations. The aim of this study was to compare and correlate various RBC indices and G6PD activity in patients with and without malaria and to find a prevalence of G6PD deficiency in a tertiary care hospital.     Materials and Methods: The present study was carried out by the Biochemistry Department of Kasturba Medical College, Manipal in 363 participants (with malaria and without malaria).  Mann Whitney U test and Spearman’s Rank correlation were employed to assess group differences and correlation, respectively.   Results: 218 cases of malaria in 365 days from a tertiary care hospital in South India is an alarming incidence and annuls the fact that the malaria prevalence is relatively low in South India. Complete blood counts and red blood indices did not show any statistically significant difference between the study groups. No statistically significant correlation was found between G6PD activity and RBC indices in the present study.   Conclusion: No significant differences between hematological indicators and malaria with or without G6PD deficiency hint towards the necessity of G6PD tests for radical treatment of malaria as hematological indices are unable to predict the defective enzyme activity.

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

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.

Care-seeking delay of imported malaria to China: implications for improving post-travel healthcare for migrant workers

BACKGROUND

Imported malaria cases continue to pose major challenges in China as well as in other countries having achieved elimination. Our study aims to identify the factors influencing the timing of care-seeking after symptom onset among migrant workers with imported malaria, in order to develop innovative interventions to improve access and provision of post-travel healthcare for returning migrants.

METHODS

We analysed the timing and types of healthcare service utilization after symptom onset among patients with imported malaria between 2012 and 2019 in Jiangsu Province, China. Moreover, decision tree models were used to explore the factors influencing the care-seeking timing after symptom onset among patients with imported malaria.

RESULTS

A total of 2255 cases of imported malaria were identified from 1 June 2012 through 31 December 2019. Patients with malaria imported into China were mainly male migrant labourers returning from sub-Saharan Africa (96.8%). A substantial number of patients with imported malaria sought healthcare >3 days after symptom onset, which clearly represented delayed healthcare-seeking behaviour. According to the decision tree analysis, initial healthcare seeking from healthcare facilities at higher administrative levels, infection with Plasmodium vivax and absence of malaria infection history were significantly associated with delayed healthcare seeking in patients with imported malaria.

CONCLUSION

The delay in seeking of medical care among migrant workers with imported malaria should be considered and addressed by specific interventions. In addition to increasing awareness about these issues among health care professionals, improved access to healthcare facilities at higher administrative levels as well as improved diagnostic capacity of healthcare facilities at lower administrative levels should be developed. Moreover, education programs targeting populations at risk of malaria importation and delayed healthcare seeking should be improved to facilitate early healthcare seeking and service use.

Plasmodium vivax Duffy Binding Protein-Based Vaccine: a Distant Dream

The neglected but highly prevalent Plasmodium vivax in South-east Asia and South America poses a great challenge, with regards to long-term in-vitro culturing and heavily limited functional assays. Such visible challenges as well as narrowed progress in development of experimental research tools hinders development of new drugs and vaccines. The leading vaccine candidate antigen Plasmodium vivax Duffy Binding Protein (PvDBP), is essential for reticulocyte invasion by binding to its cognate receptor, the Duffy Antigen Receptor for Chemokines (DARC), on the host’s reticulocyte surface. Despite its highly polymorphic nature, the amino-terminal cysteine-rich region II of PvDBP (PvDBPII) has been considered as an attractive target for vaccine-mediated immunity and has successfully completed the clinical trial Phase 1. Although this molecule is an attractive vaccine candidate against vivax malaria, there is still a question on its viability due to recent findings, suggesting that there are still some aspects which needs to be looked into further. The highly polymorphic nature of PvDBPII and strain-specific immunity due to PvDBPII allelic variation in Bc epitopes may complicate vaccine efficacy. Emergence of various blood-stage antigens, such as PvRBP, PvEBP and supposedly many more might stand in the way of attaining full protection from PvDBPII. As a result, there is an urgent need to assess and re-assess various caveats connected to PvDBP, which might help in designing a long-term promising vaccine for P. vivax malaria. This review mainly deals with a bunch of rising concerns for validation of DBPII as a vaccine candidate antigen for P. vivax malaria.

A Multiscale Mathematical Model of Plasmodium Vivax Transmission

Malaria is caused by Plasmodium parasites which are transmitted to humans by the bite of an infected Anopheles mosquito. Plasmodium vivax is distinct from other malaria species in its ability to remain dormant in the liver (as hypnozoites) and activate later to cause further infections (referred to as relapses). Mathematical models to describe the transmission dynamics of P. vivax have been developed, but most of them fail to capture realistic dynamics of hypnozoites. Models that do capture the complexity tend to involve many governing equations, making them difficult to extend to incorporate other important factors for P. vivax, such as treatment status, age and pregnancy. In this paper, we have developed a multiscale model (a system of integro-differential equations) that involves a minimal set of equations at the population scale, with an embedded within-host model that can capture the dynamics of the hypnozoite reservoir. In this way, we can gain key insights into dynamics of P. vivax transmission with a minimum number of equations at the population scale, making this framework readily scalable to incorporate more complexity. We performed a sensitivity analysis of our multiscale model over key parameters and found that prevalence of P. vivax blood-stage infection increases with both bite rate and number of mosquitoes but decreases with hypnozoite death rate. Since our mathematical model captures the complex dynamics of P. vivax and the hypnozoite reservoir, it has the potential to become a key tool to inform elimination strategies for P. vivax.

Redox aspects of cytotoxicity and anti-neuroinflammatory profile of chloroquine and hydroxychloroquine in serum-starved BV-2 microglia

Chloroquine (CQ) and hydroxychloroquine (HCQ) have long been used worldwide to treat and prevent human malarias. However, these 4-aminoquinolines have also shown promising potential in treating chronic illnesses with an inflammatory component, including neurological diseases. Given the current demand for serum avoidance during pharmacological testing and modeling of some pathologies, we compared cytotoxicities of CQ and HCQ in both serum-deprived and -fed murine BV-2 microglia. Furthermore, we assessed the anti-neuroinflammatory potential of both compounds in serum-deprived cells. Under both conditions, CQ showed higher cytotoxicity than HCQ. However, the comparable MTT-assay-derived data measured under different serum conditions were associated with disparate cytotoxic mechanisms of CQ and HCQ. In particular, under serum starvation, CQ mildly enhanced secondary ROS, mitochondrial hyperpolarization, and decreased phagocytosis. However, CQ promoted G1 phase cell cycle arrest and mitochondrial depolarization in serum-fed cells. Under both conditions, CQ fostered early apoptosis. Additionally, we confirmed that both compounds could exert anti-inflammatory effects in microglia through interference with MAPK signaling under nutrient-deprivation-related stress. Nevertheless, unlike HCQ, CQ is more likely to exaggerate intracellular prooxidant processes in activated starved microglia, which are inefficiently buffered by Nrf2/HO-1 signaling pathway activation. These outcomes also show HCQ as a promising anti-neuroinflammatory drug devoid of CQ-mediated cytotoxicity.

An open dataset of Plasmodium vivax genome variation in 1,895 worldwide samples

This report describes the MalariaGEN Pv4 dataset, a new release of curated genome variation data on 1,895 samples of Plasmodium vivax collected at 88 worldwide locations between 2001 and 2017. It includes 1,370 new samples contributed by MalariaGEN and VivaxGEN partner studies in addition to previously published samples from these and other sources. We provide genotype calls at over 4.5 million variable positions including over 3 million single nucleotide polymorphisms (SNPs), as well as short indels and tandem duplications. This enlarged dataset highlights major compartments of parasite population structure, with clear differentiation between Africa, Latin America, Oceania, Western Asia and different parts of Southeast Asia. Each sample has been classified for drug resistance to sulfadoxine, pyrimethamine and mefloquine based on known markers at the dhfr, dhps and mdr1 loci. The prevalence of all of these resistance markers was much higher in Southeast Asia and Oceania than elsewhere. This open resource of analysis-ready genome variation data from the MalariaGEN and VivaxGEN networks is driven by our collective goal to advance research into the complex biology of P. vivax and to accelerate genomic surveillance for malaria control and elimination.

Forest malaria and prospects for anti-malarial chemoprophylaxis among forest goers: findings from a qualitative study in Thailand

BACKGROUND

Across the Greater Mekong Subregion, malaria remains a dangerous infectious disease, particularly for people who visit forested areas where residual transmission continues. Because vector control measures offer incomplete protection to forest goers, chemoprophylaxis has been suggested as a potential supplementary measure for malaria prevention and control. To implement prophylaxis effectively, additional information is needed to understand forest goers' activities and their willingness to use malaria prevention measures, including prophylaxis, and how it could be delivered in communities. Drawing on in-depth interviews with forest goers and stakeholders, this article examines the potential acceptability and implementation challenges of malaria prophylaxis for forest goers in northeast Thailand.

METHODS

In-depth interviews were conducted with forest goers (n = 11) and stakeholders (n = 16) including healthcare workers, community leaders, and policymakers. Interviews were audio-recorded, transcribed and coded using NVivo, employing an inductive and deductive approach, for thematic analysis.

RESULTS

Forest goers were well aware of their (elevated) malaria risk and reported seeking care for malaria from local health care providers. Forest goers and community members have a close relationship with the forest but are not a homogenous group: their place and time-at-risk varied according to their activities and length of stay in the forest. Among stakeholders, the choice and cost of anti-malarial prophylactic regimen-its efficacy, length and complexity, number of tablets, potential side effects, and long-term impact on users-were key considerations for its feasibility. They also expressed concern about adherence to the preventive therapy and potential difficulty treating malaria patients with the same regimen. Prophylaxis was considered a low priority in areas with perceived accessible health system and approaching malaria elimination.

CONCLUSIONS

In the context of multi-drug resistance, there are several considerations for implementing malaria prophylaxis: the need to target forest goers who are at-risk with a clear period of exposure, to ensure continued use of vector control measures and adherence to prophylactic anti-malarials, and to adopt an evidence-based approach to determine an appropriate regimen. Beyond addressing current intervention challenges and managing malaria incidence in low-transmission setting, it is crucial to keep malaria services available and accessible at the village level especially in areas home to highly mobile populations.

Malaria treatment-seeking behaviour and its associated factors: A cross-sectional study in rural East Nusa Tenggara Province, Indonesia

Introduction

The World Health Organization recommends seeking medical treatment within 24 hours after transmission of malaria to reduce the risk of severe complications and its onwards spread. However, in some parts of Indonesia, including East Nusa Tenggara Province (ENTP), this adherence is not achieved for a range of reasons including delays in visiting health centres. This study aims to determine factors related to the poor understanding of appropriate malaria treatment-seeking behaviour (AMTSB) of rural adults in ENTP. AMTSB was defined as seeking treatment at professional health facilities within 24 hours of the onset of malaria symptoms.

Methods

A cross-sectional study was conducted in the East Sumba, Belu, and East Manggarai district of ENTP between October and December 2019. A multi-stage cluster sampling procedure was applied to enrol 1503 participants aged between 18 and 89 years of age. Data were collected through face-to-face interviews. Multivariable logistic regression analyses were used to assess significant factors associated with the poor understanding of AMTSB.

Results

Eighty-six percent of participants were found to be familiar with the term malaria. However, poor understanding level of AMTSB in rural adults of ENTP achieved 60.4% with a 95% confidence interval (CI): 56.9–63.8. Poor understanding of AMTSB was significantly higher for adults with no education (adjusted odds ratio (AOR) 3.42, 95% CI: 1.81, 6.48) compared to those with a diploma or above education level; having low SES (AOR: 1.87, 95% CI: 1.19, 2.96) compared to those having high SES; residing at least three kilometres (km) away from the nearest health facilities (AOR: 1.73, 95% CI: 1.2, 2.5) compared to those living within one km from the nearest health service; and working as farmer (AOR: 1.63, 95% CI: 1.01–2.63) compared to those working at government or non-government sector. Whilst, other factors such as ethnicity and family size were not associated with the poor understanding of AMTSB.

Conclusion

The proportion of rural adults having a poor understanding of AMTSB was high leading to ineffective implementation of artemisinin-based combination therapies as the method to treat malaria in ENTP. Improving awareness of AMTSB for rural adults having low level education, low SES, working as a farmer, and living at least three km from the nearest health facilities is critical to support the efficacy of malaria treatment in ENTP. This method will support the Indonesian government’s objective to achieve malaria elimination by 2030.

Comparison of the performance of the CareStart Malaria Pf/Pan Combo test and field microscopy in the diagnosis of Plasmodium vivax malaria in North Sumatera, Indonesia

Background

In areas where malaria is endemic and where trained microscopists are not available, rapid diagnostic tests (RDTs) are needed not only to allow prompt treatment without delay but also to prevent overdiagnosis and overtreatment based on clinical judgements that may lead to drug resistance. This study aimed to compare the performances of the CareStart Pf/Pan Combo test to field microscopy, which is considered to be the gold standard for malaria diagnosis.

Methods

Any person with a fever or a history of fever within 48 h who came to the health centre was recruited for the study and tested both by the CareStart Pf/Pan test and by field microscopy. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were analysed with both methods.

Results

Two-hundred study participants were enrolled: 96 (48%) were found to be positive through microscopy, while 100 (50%) participants were found to be positive through RDT. The RDT produced four false-positive results. High sensitivity and specificity were observed for the CareStart Pf/Pan test (100 and 96.15%, respectively). The CareStart Pf/Pan test also showed excellent agreement with the field microscopy results.

Conclusion

The Carestart Pf/Pan could be used as an alternative diagnostic test in malaria-endemic areas where facility for performing microscopy is not available.

Relapse of Plasmodium vivax and Plasmodium ovale malaria with and without primaquine treatment in a non-endemic area

Background

The effect of primaquine in preventing Plasmodium vivax relapses from dormant stages is well established. For Plasmodium ovale, the relapse characteristics and the use of primaquine is not as well studied. We set to evaluate the relapsing properties of these 2 species, in relation to primaquine use among imported malaria cases in a nonendemic setting.

Methods

We performed a nationwide retrospective study of malaria diagnosed in Sweden 1995–2019, by reviewing medical records of 3254 cases. All episodes of P. vivax (n = 972) and P. ovale (n = 251) were selected for analysis.

Results

First time relapses were reported in 80/857 (9.3%) P. vivax and 9/220 (4.1%) P. ovale episodes, respectively (P < .01). Without primaquine, the risk for relapse was higher in P. vivax, 20/60 (33.3%), compared to 3/30 (10.0%) in P. ovale (hazard ratio [HR] 3.5, 95% confidence interval [CI] 1.0–12.0). In P. vivax, patients prescribed primaquine had a reduced risk of relapse compared to episodes without relapse preventing treatment, 7.1% vs 33.3% (HR 0.2, 95% CI .1–.3). In P. ovale, the effect of primaquine on the risk of relapse did not reach statistical significance, with relapses seen in 2.8% of the episodes compared to 10.0% in patients not receiving relapse preventing treatment (HR 0.3, 95% CI .1–1.1).

Conclusions

The risk of relapse was considerably lower in P. ovale than in P. vivax infections indicating different relapsing features between the two species. Primaquine was effective in preventing P. vivax relapse. In P. ovale, relapse episodes were few, and the supportive evidence for primaquine remains limited.

Taking on Plasmodium vivax malaria: A timely and important challenge

Lorenz von Seidlein and Nicholas White introduce a Collection on Plasmodium vivax malaria.