Phenotypic and genotypic characterisation of drug-resistant Plasmodium vivax

Drug resistance markers in Plasmodium vivax isolates from a Kanchanaburi province, Thailand between January to May 2023

BACKGROUND

Plasmodium vivax has become the predominant species in the border regions of Thailand. The emergence and spread of antimalarial drug resistance in P. vivax is one of the significant challenges for malaria control. Continuous surveillance of drug resistance is therefore necessary for monitoring the development of drug resistance in the region. This study aims to investigate the prevalence of the mutation in the P. vivax multidrug resistant 1 (Pvmdr1), dihydrofolate reductase (Pvdhfr), and dihydropteroate synthetase (Pvdhps) genes conferred resistance to chloroquine (CQ), pyrimethamine (P) and sulfadoxine (S), respectively.

METHOD

100 P. vivax isolates were obtained between January to May 2023 from a Kanchanaburi province, western Thailand. Nucleotide sequences of Pvmdr1, Pvdhfr, and Pvdhps genes were amplified and sequenced. The frequency of single nucleotide polymorphisms (SNPs)-haplotypes of drug-resistant alleles was assessed. The linkage disequilibrium (LD) tests were also analyzed.

RESULTS

In Pvmdr1, T958M, Y976F, and F1076L, mutations were detected in 100%, 21%, and 23% of the isolates, respectively. In Pvdhfr, the quadruple mutant allele (I57R58M61T117) prevailed in 84% of the samples, followed by (L57R58M61T117) in 11%. For Pvdhps, the double mutant allele (G383G553) was detected (48%), followed by the triple mutant allele (G383M512G553) (47%) of the isolates. The most prevalent combination of Pvdhfr (I57R58M61T117) and Pvdhps (G383G553) alleles was sextuple mutated haplotypes (48%). For LD analysis, the association in the SNPs pairs was found between the intragenic and intergenic regions of the Pvdhfr and Pvdhps genes.

CONCLUSION

The study has recently updated the high prevalence of three gene mutations associated with CQ and SP resistance. Genetic monitoring is therefore important to intensify in the regions to further assess the spread of drug resistant. Our data also provide evidence on the distribution of drug resistance for the early warning system, thereby threatening P. vivax malaria treatment policy decisions at the national level.

Chloroquine has shown high therapeutic efficacy against uncomplicated Plasmodium vivax malaria in southern Ethiopia: seven decades after its introduction

BACKGROUND

Plasmodium vivax malaria is a leading cause of morbidity in Ethiopia. The first-line treatment for P. vivax is chloroquine (CQ) and primaquine (PQ), but there have been local reports of CQ resistance. A clinical study was conducted to determine the efficacy of CQ for the treatment of P. vivax malaria in southern Ethiopia.

METHODS

In 2021, patients with P. vivax mono-infection and uncomplicated malaria were enrolled and treated with 25 mg/kg CQ for 3 consecutive days. Patients were followed for 28 days according to WHO guidelines. The data were analysed using per-protocol (PP) and Kaplan‒Meier (K‒M) analyses to estimate the risk of recurrent P. vivax parasitaemia on day 28.

RESULTS

A total of 88 patients were enrolled, 78 (88.6%) of whom completed the 28 days of follow-up. Overall, 76 (97.4%) patients had adequate clinical and parasitological responses, and two patients had late parasitological failures. The initial therapeutic response was rapid, with 100% clearance of asexual parasitaemia within 48 h.

CONCLUSION

Despite previous reports of declining chloroquine efficacy against P. vivax, CQ retains high therapeutic efficacy in southern Ethiopia, supporting the current national treatment guidelines. Ongoing clinical monitoring of CQ efficacy supported by advanced molecular methods is warranted to inform national surveillance and ensure optimal treatment guidelines.

A systematic review of CQ-resistant Plasmodium vivax malaria infections in India

INTRODUCTION

Chloroquine (CQ) is the drug of choice for treating uncomplicated Plasmodium vivax (P. vivax) malaria in India. The knowledge about the exact burden of CQ resistance in P. vivax in India is scarce. Therefore, this systematic review aimed to assess the prevalence of CQ resistance in reported P. vivax cases from India.

METHODS

PubMed, EMBASE, and Web of Science, were searched using the search string: 'Malaria AND vivax AND chloroquine AND (resistance OR resistant) AND India'. We systematically reviewed in-vivo and in-vitro drug efficacy studies that investigated the CQ efficacy of P. vivax malaria between January 1995 and December 2022. Those studies where patients were followed up for at least 28 days after initiation of treatment were included.

RESULTS

We identified 12 eligible CQ therapeutic efficacy studies involving 2470 patients, Of these 2329 patients were assessed by in-vivo therapeutic efficacy methods and the remaining 141 were assessed by in-vitro methods. CQ resistance was found in 25/1787 (1.39%) patients from in-vivo and in 11/141 (7.8%) patients from in-vitro drug efficacy studies.

CONCLUSION

Based on the available studies, the prevalence of CQ resistance in P. vivax was found to be relatively lower in India. However, continued surveillance and monitoring are crucial to identify the emergence of CQ resistance.

Genomic analysis of Plasmodium vivax describes patterns of connectivity and putative drivers of adaptation in Ethiopia

Ethiopia has the greatest burden of Plasmodium vivax in Africa, but little is known about the epidemiological landscape of parasites across the country. We analysed the genomic diversity of 137 P. vivax isolates collected nine Ethiopian districts from 2012 to 2016. Signatures of selection were detected by cross-country comparisons with isolates from Thailand (n = 104) and Indonesia (n = 111), representing regions with low and high chloroquine resistance respectively. 26% (35/137) of Ethiopian infections were polyclonal, and 48.5% (17/35) of these comprised highly related clones (within-host identity-by-descent > 25%), indicating frequent co-transmission and superinfection. Parasite gene flow between districts could not be explained entirely by geographic distance, with economic and cultural factors hypothesised to have an impact on connectivity. Amplification of the duffy binding protein gene (pvdbp1) was prevalent across all districts (16-75%). Cross-population haplotype homozygosity revealed positive selection in a region proximal to the putative chloroquine resistance transporter gene (pvcrt-o). An S25P variant in amino acid transporter 1 (pvaat1), whose homologue has recently been implicated in P. falciparum chloroquine resistance evolution, was prevalent in Ethiopia (96%) but not Thailand or Indonesia (35-53%). The genomic architecture in Ethiopia highlights circulating variants of potential public health concern in an endemic setting with evidence of stable transmission.

Genomics of Plasmodium vivax in Colombia reveals evidence of local bottle-necking and inter-country connectivity in the Americas

Colombia aims to eliminate malaria by 2030 but remains one of the highest burden countries in the Americas. Plasmodium vivax contributes half of all malaria cases, with its control challenged by relapsing parasitaemia, drug resistance and cross-border spread. Using 64 Colombian P. vivax genomes collected between 2013 and 2017, we explored diversity and selection in two major foci of transmission: Chocó and Córdoba. Open-access data from other countries were used for comparative assessment of drug resistance candidates and to assess cross-border spread. Across Colombia, polyclonal infections were infrequent (12%), and infection connectivity was relatively high (median IBD = 5%), consistent with low endemicity. Chocó exhibited a higher frequency of polyclonal infections (23%) than Córdoba (7%), although the difference was not significant (P = 0.300). Most Colombian infections carried double pvdhfr (95%) and single pvdhps (71%) mutants, but other drug resistance mutations were less prevalent (< 10%). There was no evidence of selection at the pvaat1 gene, whose P. falciparum orthologue has recently been implicated in chloroquine resistance. Global population comparisons identified other putative adaptations. Within the Americas, low-level connectivity was observed between Colombia and Peru, highlighting potential for cross-border spread. Our findings demonstrate the potential of molecular data to inform on infection spread and adaptation.

No Association between the Plasmodium vivax crt-o MS334 or In9pvcrt Polymorphisms and Chloroquine Failure in a Pre-Elimination Clinical Cohort from Malaysia with a Large Clonal Expansion

Increasing reports of resistance to a frontline malaria blood-stage treatment, chloroquine (CQ), raises concerns for the elimination of Plasmodium vivax. The absence of an effective molecular marker of CQ resistance in P. vivax greatly constrains surveillance of this emerging threat. A recent genetic cross between CQ sensitive (CQS) and CQ resistant (CQR) NIH-1993 strains of P. vivax linked a moderate CQR phenotype with two candidate markers in P. vivax CQ resistance transporter gene (pvcrt-o): MS334 and In9pvcrt. Longer TGAAGH motif lengths at MS334 were associated with CQ resistance, as were shorter motifs at the In9pvcrt locus. In this study, high-grade CQR clinical isolates of P. vivax from a low endemic setting in Malaysia were used to investigate the association between the MS334 and In9pvcrt variants and treatment efficacy. Among a total of 49 independent monoclonal P. vivax isolates assessed, high-quality MS334 and In9pvcrt sequences could be derived from 30 (61%) and 23 (47%), respectively. Five MS334 and six In9pvcrt alleles were observed, with allele frequencies ranging from 2 to 76% and 3 to 71%, respectively. None of the clinical isolates had the same variant as the NIH-1993 CQR strain, and none of the variants were associated with CQ treatment failure (all P > 0.05). Multi-locus genotypes (MLGs) at 9 neutral microsatellites revealed a predominant P. vivax strain (MLG6) accounting for 52% of Day 0 infections. The MLG6 strain comprised equal proportions of CQS and CQR infections. Our study reveals complexity in the genetic basis of CQ resistance in the Malaysian P. vivax pre-elimination setting and suggests that the proposed pvcrt-o MS334 and In9pvcrt markers are not reliable markers of CQ treatment efficacy in this setting. Further studies are needed in other endemic settings, applying hypothesis-free genome-wide approaches, and functional approaches to understand the biological impact of the TGAAGH repeats linked to CQ response in a cross are warranted to comprehend and track CQR P. vivax.

Treatment of uncomplicated Plasmodium vivax with chloroquine plus radical cure with primaquine without G6PDd testing is safe in Arba Minch, Ethiopia: assessment of clinical and parasitological response

BACKGROUND

Ethiopia rolled out primaquine nationwide in 2018 for radical cure along with chloroquine for the treatment of uncomplicated Plasmodium vivax malaria in its bid for malaria elimination by 2030. The emergence of anti-malarial drug resistance would challenge the elimination goal. There is limited evidence on the emergence of chloroquine drug resistance. The clinical and parasitological outcomes of treatment of P. vivax with chloroquine plus radical cure using low dose 14 days primaquine were assessed in an endemic area of Ethiopia.

METHODS

A semi-directly observed 42-days follow up in-vivo therapeutic efficacy study was conducted from October 2019 to February 2020. Plasmodium vivax mono-species infected patients (n = 102) treated with a 14 days low dose (0.25 mg/kg body weight per day) primaquine plus chloroquine (a total dose of 25 mg base/kg for 3 days) were followed for 42 days to examine clinical and parasitological outcomes. Samples collected at recruitment and days of recurrence were examined by 18 S based nested polymerase chain reaction (nPCR) and Pvmsp3α nPCR-restriction fragment length polymorphism. Asexual parasitaemia and the presence of gametocytes were assessed on the scheduled days using microscopy. Clinical symptoms, haemoglobin levels, and Hillmen urine test were also assessed.

RESULTS

Of the 102 patients followed in this study, no early clinical and parasitological failure was observed. All patients had adequate clinical and parasitological responses within the 28 days of follow up. Late clinical (n = 3) and parasitological (n = 6) failures were observed only after day 28. The cumulative incidence of failure was 10.9% (95% confidence interval, 5.8-19.9%) on day 42. Among the paired recurrent samples, identical clones were detected only in two samples on day 0 and day of recurrences (day 30 and 42) using Pvmsp3α genotyping. No adverse effect was detected related to the low dose 14 days primaquine administrations.

CONCLUSION

Co-administration of CQ with PQ in the study area is well tolerated and there was no recurrence of P. vivax before 28 days of follow up. Interpretation of CQ plus PQ efficacy should be done with caution especially when the recurrent parasitaemia occurs after day 28. Therapeutic efficacy studies with appropriate design might be informative to rule out chloroquine or primaquine drug resistance and/or metabolism in the study area.

Retrospective analysis of Plasmodium vivax genomes from a pre-elimination China inland population in the 2010s

Introduction

In malaria-free countries, imported cases are challenging because interconnections with neighboring countries with higher transmission rates increase the risk of parasite reintroduction. Establishing a genetic database for rapidly identifying malaria importation or reintroduction is crucial in addressing these challenges. This study aimed to examine genomic epidemiology during the pre-elimination stage by retrospectively reporting whole-genome sequence variation of 10 Plasmodium vivax isolates from inland China.

Methods

The samples were collected during the last few inland outbreaks from 2011 to 2012 when China implemented a malaria control plan. After next-generation sequencing, we completed a genetic analysis of the population, explored the geographic specificity of the samples, and examined clustering of selection pressures. We also scanned genes for signals of positive selection.

Results

China's inland populations were highly structured compared to the surrounding area, with a single potential ancestor. Additionally, we identified genes under selection and evaluated the selection pressure on drug-resistance genes. In the inland population, positive selection was detected in some critical gene families, including sera, msp3, and vir. Meanwhile, we identified selection signatures in drug resistance, such as ugt, krs1, and crt, and noticed that the ratio of wild-type dhps and dhfr-ts increased after China banned sulfadoxine-pyrimethamine (SP) for decades.

Discussion

Our data provides an opportunity to investigate the molecular epidemiology of pre-elimination inland malaria populations, which exhibited lower selection pressure on invasion and immune evasion genes than neighbouring areas, but increased drug resistance in low transmission settings. Our results revealed that the inland population was severely fragmented with low relatedness among infections, despite a higher incidence of multiclonal infections, suggesting that superinfection or co-transmission events are rare in low-endemic circumstances. We identified selective signatures of resistance and found that the proportion of susceptible isolates fluctuated in response to the prohibition of specific drugs. This finding is consistent with the alterations in medication strategies during the malaria elimination campaign in inland China. Such findings could provide a genetic basis for future population studies, assessing changes in other pre-elimination countries.

A molecular barcode and web-based data analysis tool to identify imported Plasmodium vivax malaria

Traditionally, patient travel history has been used to distinguish imported from autochthonous malaria cases, but the dormant liver stages of Plasmodium vivax confound this approach. Molecular tools offer an alternative method to identify, and map imported cases. Using machine learning approaches incorporating hierarchical fixation index and decision tree analyses applied to 799 P. vivax genomes from 21 countries, we identified 33-SNP, 50-SNP and 55-SNP barcodes (GEO33, GEO50 and GEO55), with high capacity to predict the infection's country of origin. The Matthews correlation coefficient (MCC) for an existing, commonly applied 38-SNP barcode (BR38) exceeded 0.80 in 62% countries. The GEO panels outperformed BR38, with median MCCs > 0.80 in 90% countries at GEO33, and 95% at GEO50 and GEO55. An online, open-access, likelihood-based classifier framework was established to support data analysis (vivaxGEN-geo). The SNP selection and classifier methods can be readily amended for other use cases to support malaria control programs.

Genetic Diversity of Circumsporozoite Surface Protein of Plasmodium vivax from the Central Highlands, Vietnam

The circumsporozoite surface protein of Plasmodium vivax (PvCSP) plays a critical role in parasite biology. It has been extensively studied as a leading vivax-malaria-vaccine candidate. In this study, the genetic polymorphism and natural selection of pvcsp in P. vivax isolates collected from the Central Highlands, Vietnam were analyzed to understand the genetic structure of the parasite circulating in the endemic area and to provide baseline information for effective vaccine development based on the protein. Only two major alleles, VK210 and VK247, were detected in Vietnamese pvcsp, with VK247 being the predominant one. The N-terminal and C-terminal regions of Vietnamese VK210 and VK247 variants showed a low genetic diversity. Amino acid substitutions, insertions of a single amino acid or octapeptide (ANKKAEDA in VK210 and ANKKAGDA in VK247), and tetrapeptide repeat motifs (GGNA) were the main factors generating genetic diversity in the two regions of the Vietnamese VK210 and VK247 variants. Interestingly, these two regions of Vietnamese pvcsp displayed a unique natural selection pressure distinct from global pvcsp, particularly with the neighboring Southeast Asian pvcsp population. Meanwhile, the central repeat region (CRR) in both the VK210 and VK247 variants showed a high degree of polymorphic characters, caused by varying numbers, types, and combinations of peptide repeat motifs (PRMs) in Vietnamese pvcsp. Highly complicated polymorphic patterns of the CRR were also detected in global pvcsp. These results expand our understanding of the genetic structure of Vietnamese pvcsp and the population dynamics of P. vivax in the Central Highlands, Vietnam.

Antimalarial activity of solvent fractions of a leaf of Eucalyptus globulus labill against Plasmodium berghei infected mice

Introduction

The leaf of Eucalyptus globulus is commonly used in the traditional management of malaria. However, the efficacy of solvent fractions are didn’t study yet scientifically. Thus, this study aimed to investigate the antimalarial efficacy of the solvent fractions of the leaf of Eucalyptus globulus in mice against P.berghei.

Methods

The antimalarial activity of the fractions was tested in a 4-day suppressive test, Rane’s test, and prophylactic test models within P.berghei infected mice. The results were analyzed using a one-way analysis of variance (ANOVA) followed by a post hoc Tukey’s test in version 20 SPSS.

Results

All fractions at all test doses in the three test models suppressed parasitemia (p < 0.001) compared to the negative controls. In addition, the CF and EA at all three test doses and the AF at 400 mg/kg in three antimalarial test models showed 50% and above parasitemia suppression. In compliance with this, all fractions at all test doses in all test models prolonged the mean survival time of the mice greater than 12 days, except the AF at a lower dose. All fractions at 400 mg/kg in the three test models prevented (p < 0.001) loss of body weight and rectal temperature compared to the negative controls. Furthermore, all fractions in all test models and doses prevented packed cell volume reduction (p < 0.05 to p < 0.001) compared to the negative controls..

Conclusion

The findings of this study showed that CF and EAF had greater antimalarial activity compared to AF. This could be attributed to the presence of few phytochemicals in the AF in contrast to the CF and EAF. Overall, the results of this study further support the in vitro antimalarial activity study and the traditional use of the leaf in the management of malaria.

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.

Whole Genome Sequencing Contributions and Challenges in Disease Reduction Focused on Malaria

Malaria elimination remains an important goal that requires the adoption of sophisticated science and management strategies in the era of the COVID-19 pandemic. The advent of next generation sequencing (NGS) is making whole genome sequencing (WGS) a standard today in the field of life sciences, as PCR genotyping and targeted sequencing provide insufficient information compared to the whole genome. Thus, adapting WGS approaches to malaria parasites is pertinent to studying the epidemiology of the disease, as different regions are at different phases in their malaria elimination agenda. Therefore, this review highlights the applications of WGS in disease management, challenges of WGS in controlling malaria parasites, and in furtherance, provides the roles of WGS in pursuit of malaria reduction and elimination. WGS has invaluable impacts in malaria research and has helped countries to reach elimination phase rapidly by providing required information needed to thwart transmission, pathology, and drug resistance. However, to eliminate malaria in sub-Saharan Africa (SSA), with high malaria transmission, we recommend that WGS machines should be readily available and affordable in the region.

Prevalence and temporal changes of mutations linked to anti-malarial drug resistance in Plasmodium falciparum and Plasmodium vivax in Palawan, Philippines

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Plasmodium falciparum and Plasmodium vivax isolates from the Philippines were analysed.

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Varying mutations were found in markers linked to resistance to antimalarial drugs.

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None of the mutations were particularly of high prevalence.

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Clear temporal patterns in these mutations were observed within the past 15 years.

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Decrease in pfcrt and pfmdr mutations are in line with antimalarial policy change.

Objective

This study provides 2016 data on the prevalence of key single nucleotide polymorphisms (SNPs) associated with antimalarial drug resistance in Palawan, Philippines. Findings were combined with historical data to model temporal changes in the prevalence of these SNPs in Plasmodium isolates.

Methods

Plasmodium isolates were genotyped using drug resistance markers pfmdr1, pfcrt, pfdhfr, pfdhps, kelch-13, pvmdr1, pvdhfr, and pvdhps. Temporal trends in the probability of mutations were estimated as a function of time using a binomial generalised linear model.

Results

All samples sequenced for Plasmodium falciparum chloroquine markers pfmdr1 and pfcrt had wild-type alleles. Varying mutation patterns were observed for the sulphadoxine/pyrimethamine markers pfdhps and pfdhfr; complete quintuplet mutations were not found. No SNPs were observed for the artemisinin marker kelch-13. For Plasmodium vivax, differing patterns were detected for pvmdr1, pvdhfr, and pvdhps.

Conclusions

The study findings suggest that the current drugs remain effective and that there is limited importation and establishment of resistant parasites in the area. Clear temporal trends were recognised, with prominent decreases in the proportions of pfcrt and pfmdr mutations detected within the past 15 years, consistent with a change in antimalarial drug policy. Continuous surveillance of antimalarial drug resistance is important to support malaria elimination efforts.

Evaluation of the Antimalarial Activity of Crude Extract of Eucalyptus globulus Labill. Leaf against Plasmodium berghei in Mice

Introduction

Traditional medicinal plants are used as a common source of developing new and effective antimalarial drugs. E. globulus leaf has been used in the traditional management of malaria in different countries, including Ethiopia. However, there is no in vivo study done on the antimalarial activity of the plant. Thus, this study aimed to evaluate the antimalarial activity of crude extract of E. globulus Labill. leaf in P. berghei-infected mice.

Method

The fresh leaves of E. globulus were collected, washed, air-dried, and made as coarse powder. Either sex of mice aged 6 to 8 weeks was used in the experiment. The antimalarial activity of the crude extract was tested in four-day suppressive, curative (Rane's), and prophylactic (repository) tests. The parameters like level of parasitemia, packed cell volume, body weight, rectal temperature, and mean survival time were recorded. The analysis of the data was done with SPSS version 20 with a 95% confidence interval in one-way ANOVA followed by Tukey's post hoc test.

Results

In all three antimalarial test models, the extract of leaf of E. globulus at all three doses suppressed the level of parasitemia significantly (p < 0.001), increased survival time (p < 0.05 to p < 0.001), and prevented a decrease in body weight as compared to the negative control. The middle and large doses of the extract also decreased loss of body temperature (p < 0.05 to p < 0.001) compared to the negative control. Reduction of packed cell volume was prevented within the three test doses of the extract in both curative and prophylactic tests and middle and large doses in the 4-day suppressive test compared to the negative control.

Conclusion

The crude extract of the plant showed promising antimalarial activity. This supports the traditional use and the in vitro test result of the plant.

High Proportion of Genome-Wide Homology and Increased Pretreatment pvcrt Levels in Plasmodium vivax Late Recurrences: a Chloroquine Therapeutic Efficacy Study

Chloroquine (CQ) is the first-line treatment for Plasmodium vivax malaria in most countries where malaria is endemic. Monitoring P. vivax CQ resistance (CQR) is critical but remains challenged by the difficulty to distinguish real treatment failure from reinfection or liver relapse. The therapeutic efficacy of CQ against uncomplicated P. vivax malaria was evaluated in Gia Lai Province, Vietnam. Sixty-seven patients were enrolled and followed for 42 days using microscopy and quantitative PCR. Adequate clinical and parasitological response (ACPR) was 100% (66/66) on day 28 but 75.4% (49/65) on day 42. Eighteen recurrences (27.7%) were detected, with a median time to recurrence of 42 days (interquartile range [IQR], 35 to 42) and blood CQ concentration of <100 ng/ml. Primary infections leading to recurrence occurred in younger individuals (median age for ACPR = 25 years [IQR, 20 to 28]; recurrences = 18 [16 to 21]; P = 0.002) had a longer parasite clearance time (PCT for ACPR = 47.5 h [IQR, 36.2 to 59.8 h]; recurrences = 54.2 [48.4 to 62.0]; P = 0.035) and higher pvcrt gene expression (median relative expression ratio for ACPR = 0.09 [IQR, 0.05 to 0.22]; recurrences = 0.20 [0.15 to 0.56]; P = 0.002), but showed no differences in ex vivo CQ sensitivity. Parasite genotyping by microsatellites, single nucleotide polymorphism (SNP) barcoding, and whole-genome sequencing (WGS) identified a majority of homologous recurrences, with 80% (8/10) showing >98% identity by descent to paired day 0 samples. This study shows that CQ remained largely efficacious to treat P. vivax in Gia Lai; i.e., recurrences occurred late (>day 28) and in the presence of low blood CQ concentrations. However, the combination of both WGS and gene expression analysis (pvcrt) data with clinical data (PCT) allowed us to identify potential emergence of low-grade CQR, which should be closely monitored. (This study has been registered at ClinicalTrials.gov under identifier NCT02610686.).

The changing epidemiology of Plasmodium vivax: Insights from conventional and novel surveillance tools

Sarah Auburn and co-authors discuss the unique biology and epidemiology of P. vivax and current evidence on conventional and new approaches to surveillance.

Monitoring Plasmodium vivax resistance to antimalarials: Persisting challenges and future directions

Emerging antimalarial drug resistance may undermine current efforts to control and eliminate Plasmodium vivax, the most geographically widespread yet neglected human malaria parasite. Endemic countries are expected to assess regularly the therapeutic efficacy of antimalarial drugs in use in order to adjust their malaria treatment policies, but proper funding and trained human resources are often lacking to execute relatively complex and expensive clinical studies, ideally complemented by ex vivo assays of drug resistance. Here we review the challenges for assessing in vivo P. vivax responses to commonly used antimalarials, especially chloroquine and primaquine, in the presence of confounding factors such as variable drug absorption, metabolism and interaction, and the risk of new infections following successful radical cure. We introduce a simple modeling approach to quantify the relative contribution of relapses and new infections to recurring parasitemias in clinical studies of hypnozoitocides. Finally, we examine recent methodological advances that may render ex vivo assays more practical and widely used to confirm P. vivax drug resistance phenotypes in endemic settings and review current approaches to the development of robust genetic markers for monitoring chloroquine resistance in P. vivax populations.

Multi-locus genotyping reveals established endemicity of a geographically distinct Plasmodium vivax population in Mauritania, West Africa

BACKGROUND

Plasmodium vivax has been recently discovered as a significant cause of malaria in Mauritania, although very rare elsewhere in West Africa. It has not been known if this is a recently introduced or locally remnant parasite population, nor whether the genetic structure reflects epidemic or endemic transmission.

METHODOLOGY/PRINCIPAL FINDINGS

To investigate the P. vivax population genetic structure in Mauritania and compare with populations previously analysed elsewhere, multi-locus genotyping was undertaken on 100 clinical isolates, using a genome-wide panel of 38 single nucleotide polymorphisms (SNPs), plus seven SNPs in drug resistance genes. The Mauritanian P. vivax population is shown to be genetically diverse and divergent from populations elsewhere, indicated consistently by genetic distance matrix analysis, principal components analyses, and fixation indices. Only one isolate had a genotype clearly indicating recent importation, from a southeast Asian source. There was no linkage disequilibrium in the local parasite population, and only a small number of infections appeared to be closely genetically related, indicating that there is ongoing genetic recombination consistent with endemic transmission. The P. vivax diversity in a remote mining town was similar to that in the capital Nouakchott, with no indication of local substructure or of epidemic population structure. Drug resistance alleles were virtually absent in Mauritania, in contrast with P. vivax in other areas of the world.

CONCLUSIONS/SIGNIFICANCE

The molecular epidemiology indicates that there is long-standing endemic transmission that will be very challenging to eliminate. The virtual absence of drug resistance alleles suggests that most infections have been untreated, and that this endemic infection has been more neglected in comparison to P. vivax elsewhere.

Estimating the Proportion of Plasmodium vivax Recurrences Caused by Relapse: A Systematic Review and Meta-Analysis

Plasmodium vivax and Plasmodium ovale form dormant liver hypnozoites that can reactivate weeks to months following initial infection. Malaria recurrences caused by relapses are an important cause of morbidity and source of transmission. To estimate the proportions of P. vivax malaria recurrences caused by relapses in different geographical locations, we systematically reviewed clinical efficacy studies of uncomplicated P. vivax malaria, in which patients were randomized to treatment with or without radical cure primaquine regimens and were followed up for 1 year. The minimum proportion of recurrences caused by relapses was estimated for each study site by assuming primaquine prevented all relapses and did not augment blood-stage efficacy. Of the 261 studies identified, six were eligible enrolling 4,092 patients from 14 treatment arm comparisons across seven countries. Of the 2,735 patients treated with primaquine, 24.3% received low dose (2.5 to < 5.0 mg/kg total) and 75.7% received high-dose primaquine (≥ 5.0 mg/kg total). The overall pooled incidence rate ratio of P. vivax relapses for patients treated with primaquine versus no primaquine was 0.15 (95% CI: 0.10-0.21; I ² = 83.3%), equating to a minimum of 79% of recurrences attributable to relapse. Country-specific incidence rate ratios ranged from 0.05 (95% CI: 0.01-0.34; one estimate) in Pakistan to 0.34 in Nepal (95% CI: 0.12-0.83; one estimate) and Afghanistan (95% CI: 0.22-0.51; three estimates). Relapses account for a very high proportion of recurrent infections following schizontocidal treatment of acute P. vivax malaria across diverse geographic locations. This emphasizes the importance of implementing hypnozoitocidal treatment.

Molecular surveillance for drug resistance markers in Plasmodium vivax isolates from symptomatic and asymptomatic infections at the China-Myanmar border

BACKGROUND

In the Greater Mekong sub-region, Plasmodium vivax has become the predominant species and imposes a major challenge for regional malaria elimination. This study aimed to investigate the variations in genes potentially related to drug resistance in P. vivax populations from the China-Myanmar border area. In addition, this study also wanted to determine whether divergence existed between parasite populations associated with asymptomatic and acute infections.

METHODS

A total of 66 P. vivax isolates were obtained from patients with acute malaria who attended clinics at the Laiza area, Kachin State, Myanmar in 2015. In addition, 102 P. vivax isolates associated with asymptomatic infections were identified by screening of volunteers without signs or symptoms from surrounding villages. Slide-positive samples were verified with nested PCR detecting the 18S rRNA gene. Multiclonal infections were further excluded by genotyping at msp-3α and msp-3β genes. Parasite DNA from 60 symptomatic cases and 81 asymptomatic infections was used to amplify and sequence genes potentially associated with drug resistance, including pvmdr1, pvcrt-o, pvdhfr, pvdhps, and pvk12.

RESULTS

The pvmdr1 Y976F and F1076L mutations were present in 3/113 (2.7%) and 97/113 (85.5%) P. vivax isolates, respectively. The K10 insertion in pvcrt-o gene was found in 28.2% of the parasites. Four mutations in the two antifolate resistance genes reached relatively high levels of prevalence: pvdhfr S58R (53.4%), S117N/T (50.8%), pvdhps A383G (75.0%), and A553G (36.3%). Haplotypes with wild-type pvmdr1 (976Y/997K/1076F) and quadruple mutations in pvdhfr (13I/57L/58R/61M/99H/117T/173I) were significantly more prevalent in symptomatic than asymptomatic infections, whereas the pvmdr1 mutant haplotype 976Y/997K/1076L was significantly more prevalent in asymptomatic than symptomatic infections. In addition, quadruple mutations at codons 57, 58, 61 and 117 of pvdhfr and double mutations at codons 383 and 553 of pvdhps were found both in asymptomatic and symptomatic infections with similar frequencies. No mutations were found in the pvk12 gene.

CONCLUSIONS

Mutations in pvdhfr and pvdhps were prevalent in both symptomatic and asymptomatic P. vivax infections, suggestive of resistance to antifolate drugs. Asymptomatic carriers may act as a silent reservoir sustaining drug-resistant parasite transmission necessitating a rational strategy for malaria elimination in this region.

Population genomics identifies a distinct Plasmodium vivax population on the China-Myanmar border of Southeast Asia

Plasmodium vivax has become the predominant malaria parasite and a major challenge for malaria elimination in the Greater Mekong Subregion (GMS). Yet, our knowledge about the evolution of P. vivax populations in the GMS is fragmental. We performed whole genome sequencing on 23 P. vivax samples from the China-Myanmar border (CMB) and used 21 high-coverage samples to compare to over 200 samples from the rest of the GMS. Using genome-wide single nucleotide polymorphisms (SNPs), we analyzed population differentiation, genetic structure, migration and potential selection using an array of methods. The CMB parasites displayed a higher proportion of monoclonal infections, and 52% shared over 90% of their genomes in identity-by-descent segments with at least one other sample from the CMB, suggesting preferential expansion of certain parasite strains in this region, likely resulting from the P. vivax outbreaks occurring during this study period. Principal component, admixture, fixation index and phylogenetic analyses all identified that parasites from the CMB were genetically distinct from parasites from eastern parts of the GMS (Cambodia, Laos, Vietnam, and Thailand), whereas the eastern GMS parasite populations were largely undifferentiated. Such a genetic differentiation pattern of the P. vivax populations from the GMS parasite was largely explainable through geographic distance. Using the genome-wide SNPs, we narrowed down to a set of 36 SNPs for differentiating parasites from different areas of the GMS. Genome-wide scans to determine selection in the genome with two statistical methods identified genes potentially under drug selection, including genes associated with antifolate resistance and genes linked to chloroquine resistance in Plasmodium falciparum.

Implementing parasite genotyping into national surveillance frameworks: feedback from control programmes and researchers in the Asia-Pacific region

The Asia-Pacific region faces formidable challenges in achieving malaria elimination by the proposed target in 2030. Molecular surveillance of Plasmodium parasites can provide important information on malaria transmission and adaptation, which can inform national malaria control programmes (NMCPs) in decision-making processes. In November 2019 a parasite genotyping workshop was held in Jakarta, Indonesia, to review molecular approaches for parasite surveillance and explore ways in which these tools can be integrated into public health systems and inform policy. The meeting was attended by 70 participants from 8 malaria-endemic countries and partners of the Asia Pacific Malaria Elimination Network. The participants acknowledged the utility of multiple use cases for parasite genotyping including: quantifying the prevalence of drug resistant parasites, predicting risks of treatment failure, identifying major routes and reservoirs of infection, monitoring imported malaria and its contribution to local transmission, characterizing the origins and dynamics of malaria outbreaks, and estimating the frequency of Plasmodium vivax relapses. However, the priority of each use case varies with different endemic settings. Although a one-size-fits-all approach to molecular surveillance is unlikely to be applicable across the Asia-Pacific region, consensus on the spectrum of added-value activities will help support data sharing across national boundaries. Knowledge exchange is needed to establish local expertise in different laboratory-based methodologies and bioinformatics processes. Collaborative research involving local and international teams will help maximize the impact of analytical outputs on the operational needs of NMCPs. Research is also needed to explore the cost-effectiveness of genetic epidemiology for different use cases to help to leverage funding for wide-scale implementation. Engagement between NMCPs and local researchers will be critical throughout this process.

An unlabelled probe-based real time PCR and modified semi-nested PCR as molecular tools for analysis of chloroquine resistant Plasmodium vivax isolates from Afghanistan

Background

Plasmodium vivax resistance to chloroquine (CQ) has been reported from many endemic regions in the world. Plasmodium vivax is responsible for 95% of malaria cases in Afghanistan and CQ is the first-line treatment given for vivax malaria. The pvmdr-1 and pvcrt-o (K10 insertion) genes are possible markers for CQ-resistance in P. vivax isolates. There have been no studies done on the presence or absence of molecular markers for CQ-resistance P. vivax in Afghanistan. The present work aimed to evaluate the frequency of mutations in the pvmdr-1 and K10 insertion in the pvcrt-o genes of P. vivax.

Methods

Plasmodium vivax isolates were collected from Laghman, Baghlan and Khost provinces. For investigation of polymorphisms of desired regions in pvmdr-1 and pvcrt-o genes, sequencing was applied on the PCR products. A new asymmetric qPCR and melting analysis assay based on unlabelled probe developed for scanning of K10 insertion in pvcrt-o gene.

Results

The analysis of sequencing data of the pvmdr-1 gene showed wild type Y976 and K997 and mutant M958 and L1076 in 33 isolates from three provinces. Of the 36 samples evaluated for K10 insertion in pvcrt-o, 2/18(11%), 0/10(0%) and 0/8(0%) isolates from Laghman, Baghlan and Khost province, respectively, possessed K10 insertion, confirmed by either sequencing and unlabelled probes.

Conclusion

Two samples with K10 insertion and 33 samples with pvmdr1 polymorphism, indicating on the possibility of CQ resistance in P. vivax populations in Afghanistan. Furthermore, unlabelled probes are simple and inexpensive alternative tools for screening of P. vivax mutations.

Ex vivo susceptibilities of Plasmodium vivax isolates from the China-Myanmar border to antimalarial drugs and association with polymorphisms in Pvmdr1 and Pvcrt-o genes

BACKGROUND

Vivax malaria is an important public health problem in the Greater Mekong Subregion (GMS), including the China-Myanmar border. Previous studies have found that Plasmodium vivax has decreased sensitivity to antimalarial drugs in some areas of the GMS, but the sensitivity of P. vivax to antimalarial drugs is unclear in the China-Myanmar border. Here, we investigate the drug sensitivity profile and genetic variations for two drug resistance related genes in P. vivax isolates to provide baseline information for future drug studies in the China-Myanmar border.

METHODOLOGY/PRINCIPAL FINDINGS

A total of 64 P. vivax clinical isolates collected from the China-Myanmar border area were assessed for ex vivo susceptibility to eight antimalarial drugs by the schizont maturation assay. The medians of IC50 (half-maximum inhibitory concentrations) for chloroquine, mefloquine, pyronaridine, piperaquine, quinine, artesunate, artemether, dihydroartemisinin were 84.2 nM, 34.9 nM, 4.0 nM, 22.3 nM, 41.4 nM, 2.8 nM, 2.1 nM and 2.0 nM, respectively. Twelve P. vivax clinical isolates were found over the cut-off IC50 value (220 nM) for chloroquine resistance. In addition, sequence polymorphisms in pvmdr1 (P. vivax multidrug resistance-1), pvcrt-o (P. vivax chloroquine resistance transporter-o), and difference in pvmdr1 copy number were studied. Sequencing of the pvmdr1 gene in 52 samples identified 12 amino acid substitutions, among which two (G698S and T958M) were fixed, M908L were present in 98.1% of the isolates, while Y976F and F1076L were present in 3.8% and 78.8% of the isolates, respectively. Amplification of the pvmdr1 gene was only detected in 4.8% of the samples. Sequencing of the pvcrt-o in 59 parasite isolates identified a single lysine insertion at position 10 in 32.2% of the isolates. The pvmdr1 M908L substitutions in pvmdr1 in our samples was associated with reduced sensitivity to chloroquine, mefloquine, pyronaridine, piperaquine, quinine, artesunate and dihydroartemisinin.

CONCLUSIONS

Our findings depict a drug sensitivity profile and genetic variations of the P. vivax isolates from the China-Myanmar border area, and suggest possible emergence of chloroquine resistant P. vivax isolates in the region, which demands further efforts for resistance monitoring and mechanism studies.

Plasmodium vivax in the Era of the Shrinking P. falciparum Map

Plasmodium vivax is an important cause of malaria, associated with a significant public health burden. Whilst enhanced malaria-control activities have successfully reduced the incidence of Plasmodium falciparum malaria in many areas, there has been a consistent increase in the proportion of malaria due to P. vivax in regions where both parasites coexist. This article reviews the epidemiology and biology of P. vivax, how the parasite differs from P. falciparum, and the key features that render it more difficult to control and eliminate. Since transmission of the parasite is driven largely by relapses from dormant liver stages, its timely elimination will require widespread access to safe and effective radical cure.

Early transmission of sensitive strain slows down emergence of drug resistance in Plasmodium vivax

The spread of drug resistance of Plasmodium falciparum and Plasmodium vivax parasites is a challenge towards malaria elimination. P. falciparum has shown an early and severe drug resistance in comparison to P. vivax in various countries. In fact, P. vivax differs in its life cycle and treatment in various factors: development and duration of sexual parasite forms differ, symptoms severity are unequal, relapses present only in P. vivax cases and the Artemisinin-based combination therapy (ACT) is only mandatory in P. falciparum cases. We compared the spread of drug resistance for both species through two compartmental models using ordinary differential equations. The model structure describes how sensitive and resistant parasite strains infect a human population treated with antimalarials. We found that an early transmission,i.e., before treatment and low effectiveness of drug coverage, supports the prevalence of sensitive parasites delaying the emergence of resistant P. vivax. These results imply that earlier attention of both symptomatic cases and reservoirs of P. vivax are essential in controlling transmission but also accelerate the spread of drug resistance.

Molecular detection of antimalarial drug resistance in Plasmodium vivax from returned travellers to NSW, Australia during 2008-2018

To monitor drug resistance in Plasmodium vivax, a multidrug resistance 1 (Pvmdr1) gene and a putative transporter protein (Pvcrt-o) gene were used as molecular markers for chloroquine resistance. The biomarkers, the dihydrofolate reductase (Pvdhfr) gene and the dihydropteroate synthetase (Pvdhps) gene, were also used for the detection of resistance to sulphadoxine-pyrimethamine (SP); this drug is often accidentally used to treat P. vivax infections. Clinical blood samples (n = 120) were collected from patients who had been to one of eight malaria-endemic countries and diagnosed with P. vivax infection. The chloroquine resistance marker, the Pvmdr1 gene, showed F976:L1076 mutations and L1076 mutation. A K10 insertion in the Pvcrt-o gene was also found among the samples successfully sequenced. A combination of L/I57:R58:M61:T117 mutations in the Pvdhfr gene and G383:G553 mutations in the Pvdhps gene were also observed. Mutations found in these genes indicate that drug resistance is present in these eight countries. Whether or not countries are using chloroquine to treat P. vivax, there appears to be an increase in mutation numbers in resistance gene markers. The detected changes in mutation rates of these genes do suggest that there is still a trend towards increasing P. vivax resistance to chloroquine. The presence of the mutations associated with SP resistance indicates that P. vivax has had exposure to SP and this may be a consequence of either misdiagnosis or coinfections with P. falciparum in the past.

Genomic Analysis of Plasmodium vivax in Southern Ethiopia Reveals Selective Pressures in Multiple Parasite Mechanisms

The Horn of Africa harbors the largest reservoir of Plasmodium vivax in the continent. Most of sub-Saharan Africa has remained relatively vivax-free due to a high prevalence of the human Duffy-negative trait, but the emergence of strains able to invade Duffy-negative reticulocytes poses a major public health threat. We undertook the first population genomic investigation of P. vivax from the region, comparing the genomes of 24 Ethiopian isolates against data from Southeast Asia to identify important local adaptions. The prevalence of the Duffy binding protein amplification in Ethiopia was 79%, potentially reflecting adaptation to Duffy negativity. There was also evidence of selection in a region upstream of the chloroquine resistance transporter, a putative chloroquine-resistance determinant. Strong signals of selection were observed in genes involved in immune evasion and regulation of gene expression, highlighting the need for a multifaceted intervention approach to combat P. vivax in the region.

Molecular detection of drug resistant malaria in Southern Thailand

BACKGROUND

Drug resistance within the major malaria parasites Plasmodium vivax and Plasmodium falciparum threatens malaria control and elimination in Southeast Asia. Plasmodium vivax first-line treatment drug is chloroquine together with primaquine, and the first-line treatment for P. falciparum malaria is artemisinin in combination with a partner drug. Plasmodium vivax and P. falciparum parasites resistant to their respective first-line therapies are now found within Southeast Asia. The resistance perimeters may include high transmission regions of Southern Thailand which are underrepresented in surveillance efforts.

METHODS

This study investigated blood samples from malaria centres in Southern Thailand. Genetic loci associated with drug resistance were amplified and sequenced. Drug resistance associated genes Pvmdr1, Pvcrt-o, Pvdhfr, and Pvdhps were characterized for 145 cases of P. vivax malaria, as well as the artemisinin resistance-associated Pfkelch13 gene from 91 cases of P. falciparum malaria.

RESULTS

Plasmodium vivax samples from Southern Thai provinces showed numerous chloroquine and antifolate resistance-associated mutations, including SNP and Pvcrt-o K10-insertion combinations suggestive of chloroquine resistant P. vivax phenotypes. A high proportion of the C580Y coding mutation (conferring artemisinin resistance) was detected in P. falciparum samples originating from Ranong and Yala (where the mutation was previously unreported).

CONCLUSIONS

The results demonstrate a risk of chloroquine and antifolate resistant P. vivax phenotypes in Southern Thailand, and artemisinin resistant P. falciparum observed as far south as the Thai-Malaysian border region. Ongoing surveillance of antimalarial drug resistance markers is called for in Southern Thailand to inform case management.

Plasmodium knowlesi as a model system for characterising Plasmodium vivax drug resistance candidate genes

Plasmodium vivax causes the majority of malaria outside Africa, but is poorly understood at a cellular level partly due to technical difficulties in maintaining it in in vitro culture conditions. In the past decades, drug resistant P. vivax parasites have emerged, mainly in Southeast Asia, but while some molecular markers of resistance have been identified, none have so far been confirmed experimentally, which limits interpretation of the markers, and hence our ability to monitor and control the spread of resistance. Some of these potential markers have been identified through P. vivax genome-wide population genetic analyses, which highlighted genes under recent evolutionary selection in Southeast Asia, where chloroquine resistance is most prevalent. These genes could be involved in drug resistance, but no experimental proof currently exists to support this hypothesis. In this study, we used Plasmodium knowlesi, the most closely related species to P. vivax that can be cultured in human erythrocytes, as a model system to express P. vivax genes and test for their role in drug resistance. We adopted a strategy of episomal expression, and were able to express fourteen P. vivax genes, including two allelic variants of several hypothetical resistance genes. Their expression level and localisation were assessed, confirming cellular locations conjectured from orthologous species, and suggesting locations for several previously unlocalised proteins, including an apical location for PVX_101445. These findings establish P. knowlesi as a suitable model for P. vivax protein expression. We performed chloroquine and mefloquine drug assays, finding no significant differences in drug sensitivity: these results could be due to technical issues, or could indicate that these genes are not actually involved in drug resistance, despite being under positive selection pressure in Southeast Asia. These data confirm that in vitro P. knowlesi is a useful tool for studying P. vivax biology. Its close evolutionary relationship to P. vivax, high transfection efficiency, and the availability of markers for colocalisation, all make it a powerful model system. Our study is the first of its kind using P. knowlesi to study unknown P. vivax proteins and investigate drug resistance mechanisms.

Use cases for genetic epidemiology in malaria elimination

Background

While traditional epidemiological approaches have supported significant reductions in malaria incidence across many countries, higher resolution information about local and regional malaria epidemiology will be needed to efficiently target interventions for elimination. The application of genetic epidemiological methods for the analysis of parasite genetics has, thus far, primarily been confined to research settings. To illustrate how these technical methods can be used to advance programmatic and operational needs of National Malaria Control Programmes (NMCPs), and accelerate global progress to eradication, this manuscript presents seven use cases for which genetic epidemiology approaches to parasite genetic data are informative to the decision-making of NMCPs.

Methods

The use cases were developed through a highly iterative process that included an extensive review of the literature and global guidance documents, including the 2017 World Health Organization’s Framework for Malaria Elimination, and collection of stakeholder input. Semi-structured interviews were conducted with programmatic and technical experts about the needs and opportunities for genetic epidemiology methods in malaria elimination.

Results

Seven use cases were developed: Detect resistance, Assess drug resistance gene flow, Assess transmission intensity, Identify foci, Determine connectivity of parasite populations, Identify imported cases, and Characterize local transmission chains. The method currently used to provide the information sought, population unit for implementation, the pre-conditions for using these approaches, and post-conditions intended as a product of the use case were identified for each use case.

Discussion

This framework of use cases will prioritize research and development of genetic epidemiology methods that best achieve the goals of NMCPs, and ultimately, inform the establishment of normative policy guidance for their uses. With significant engagement of stakeholders from malaria endemic countries and collaboration with local programme experts to ensure strategic implementation, genetic epidemiological approaches have tremendous potential to accelerate global malaria elimination efforts.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2784-0) contains supplementary material, which is available to authorized users.

Monitoring the Efficacy of Chloroquine-Primaquine Therapy for Uncomplicated Plasmodium vivax Malaria in the Main Transmission Hot Spot of Brazil

Emerging Plasmodium vivax resistance to chloroquine (CQ) may undermine malaria elimination efforts in South America. CQ-resistant P. vivax has been found in the major port city of Manaus but not in the main malaria hot spots across the Amazon Basin of Brazil, where CQ is routinely coadministered with primaquine (PQ) for radical cure of vivax malaria. Here we randomly assigned 204 uncomplicated vivax malaria patients from Juruá Valley, northwestern Brazil, to receive either sequential (arm 1) or concomitant (arm 2) CQ-PQ treatment. Because PQ may synergize the blood schizontocidal effect of CQ and mask low-level CQ resistance, we monitored CQ-only efficacy in arm 1 subjects, who had PQ administered only at the end of the 28-day follow-up. We found adequate clinical and parasitological responses in all subjects assigned to arm 2. However, 2.2% of arm 1 patients had microscopy-detected parasite recrudescences at day 28. When PCR-detected parasitemias at day 28 were considered, response rates decreased to 92.1% and 98.8% in arms 1 and 2, respectively. Therapeutic CQ levels were documented in 6 of 8 recurrences, consistent with true CQ resistance in vivo In contrast, ex vivo assays provided no evidence of CQ resistance in 49 local P. vivax isolates analyzed. CQ-PQ coadministration was not found to potentiate the antirelapse efficacy of PQ over 180 days of surveillance; however, we suggest that larger studies are needed to examine whether and how CQ-PQ interactions, e.g., CQ-mediated inhibition of PQ metabolism, modulate radical cure efficacy in different P. vivax-infected populations. (This study has been registered at ClinicalTrials.gov under identifier NCT02691910.).

The effect of chloroquine dose and primaquine on Plasmodium vivax recurrence: a WorldWide Antimalarial Resistance Network systematic review and individual patient pooled meta-analysis

BACKGROUND

Chloroquine remains the mainstay of treatment for Plasmodium vivax malaria despite increasing reports of treatment failure. We did a systematic review and meta-analysis to investigate the effect of chloroquine dose and the addition of primaquine on the risk of recurrent vivax malaria across different settings.

METHODS

A systematic review done in MEDLINE, Web of Science, Embase, and Cochrane Database of Systematic Reviews identified P vivax clinical trials published between Jan 1, 2000, and March 22, 2017. Principal investigators were invited to share individual patient data, which were pooled using standardised methods. Cox regression analyses with random effects for study site were used to investigate the roles of chloroquine dose and primaquine use on rate of recurrence between day 7 and day 42 (primary outcome). The review protocol is registered in PROSPERO, number CRD42016053310.

FINDINGS

Of 134 identified chloroquine studies, 37 studies (from 17 countries) and 5240 patients were included. 2990 patients were treated with chloroquine alone, of whom 1041 (34·8%) received a dose below the target 25 mg/kg. The risk of recurrence was 32·4% (95% CI 29·8-35·1) by day 42. After controlling for confounders, a 5 mg/kg higher chloroquine dose reduced the rate of recurrence overall (adjusted hazard ratio [AHR] 0·82, 95% CI 0·69-0·97; p=0·021) and in children younger than 5 years (0·59, 0·41-0·86; p=0·0058). Adding primaquine reduced the risk of recurrence to 4·9% (95% CI 3·1-7·7) by day 42, which is lower than with chloroquine alone (AHR 0·10, 0·05-0·17; p<0·0001).

INTERPRETATION

Chloroquine is commonly under-dosed in the treatment of vivax malaria. Increasing the recommended dose to 30 mg/kg in children younger than 5 years could reduce substantially the risk of early recurrence when primaquine is not given. Radical cure with primaquine was highly effective in preventing early recurrence and may also improve blood schizontocidal efficacy against chloroquine-resistant P vivax.

FUNDING

Wellcome Trust, Australian National Health and Medical Research Council, and Bill & Melinda Gates Foundation.

Genomic analysis of a pre-elimination Malaysian Plasmodium vivax population reveals selective pressures and changing transmission dynamics

The incidence of Plasmodium vivax infection has declined markedly in Malaysia over the past decade despite evidence of high-grade chloroquine resistance. Here we investigate the genetic changes in a P. vivax population approaching elimination in 51 isolates from Sabah, Malaysia and compare these with data from 104 isolates from Thailand and 104 isolates from Indonesia. Sabah displays extensive population structure, mirroring that previously seen with the emergence of artemisinin-resistant P. falciparum founder populations in Cambodia. Fifty-four percent of the Sabah isolates have identical genomes, consistent with a rapid clonal expansion. Across Sabah, there is a high prevalence of loci known to be associated with antimalarial drug resistance. Measures of differentiation between the three countries reveal several gene regions under putative selection in Sabah. Our findings highlight important factors pertinent to parasite resurgence and molecular cues that can be used to monitor low-endemic populations at the end stages of P. vivax elimination.

Molecular evaluation of pvdhfr and pvmdr-1 mutants in Plasmodium vivax isolates after treatment with sulfadoxine/pyrimethamine and chloroquine in Iran during 2001-2016

The rising use of sulfadoxine/pyrimethamine (SP) in the treatment of chloroquine (CQ)-resistant Plasmodium falciparum has resulted in increased exposure to P. vivax isolates in Iran, where both species are being circulated. In this investigation, the frequency of pvdhfr and pvmdr-1 mutants was assessed in P. vivax strains during 2001-2016 after the introduction of SP/CQ in malarious areas of Iran. The P. vivax isolates (n, 52) were obtained from autochthonous samples in Southeast Iran during 2015-2016. The genomic DNA was extracted and examined using nested polymerase chain reaction-(PCR) and sequencing. Mutations were detected in pvdhfr codons P33L (21.2%), T61 M (25%), S93H (3.9%), and S117 T (1.9%) and 5 isolates showed double mutations (33 L/61 M, 7.7%; 33 L/117 T, 1.9%). No mutation was identified in pvdhfr codons F57 and S58. The pvmdr-1 1076 L mutation was detected in 93.3% of P. vivax isolates. The findings indicated that the frequency of three codons of pvdhfr F57/S58/S117 has decreased from 2001 (1.05%/7.0%/16.9%) to 2016 (0%/0%/1.9%). Genomic analysis of pvmdr-1 showed that the frequency of 1076 L has gradually increased from 2013 (93%) to 2016 (93.3%) (P > .05). The results demonstrated that P. vivax isolates are probably being exited under SP pressure, which reflects the appropriate level of training for field microscopists, as established by Iranian policymakers. Emergent pvdhfr codons 33L, 61M, and 93H should be noticed in plausible drug tolerance and treatment plans. The high prevalence of pvmdr-1 1076L mutation shows that efficacy of CQ combination with primaquine may be in danger of being compromised, however further investigations are needed to evaluate the clinical importance of CQ-resistant P. vivax isolates.

Simultaneous detection of Plasmodium vivax dhfr, dhps, mdr1 and crt-o resistance-associated mutations in the Colombian Amazonian region

Background

Malaria continues being a public health problem worldwide. Plasmodium vivax is the species causing the largest number of cases of malaria in Asia and South America. Due to the lack of a completely effective anti-malarial vaccine, controlling this disease has been based on transmission vector management, rapid diagnosis and suitable treatment. However, parasite resistance to anti-malarial drugs has become a major yet-to-be-overcome challenge. This study was thus aimed at determining pvmdr1, pvdhfr, pvdhps and pvcrt-o gene mutations and haplotypes from field samples obtained from an endemic area in the Colombian Amazonian region.

Methods

Fifty samples of parasite DNA infected by a single P. vivax strain from symptomatic patients from the Amazonas department in Colombia were analysed by PCR and the pvdhfr, pvdhps, pvmdr1 and pvcrt-o genes were sequenced. Diversity estimators were calculated from the sequences and the haplotypes circulating in the Colombian Amazonian region were obtained.

Conclusion

pvdhfr, pvdhps, pvmdr1 and pvcrt-o genes in the Colombian Amazonian region are characterized by low genetic diversity. Some resistance-associated mutations were found circulating in this population. New variants are also being reported. A selective sweep signal was located in pvdhfr and pvmdr1 genes, suggesting that these mutations (or some of them) could be providing an adaptive advantage.

Enhanced Ex Vivo Plasmodium vivax Intraerythrocytic Enrichment and Maturation for Rapid and Sensitive Parasite Growth Assays

Plasmodium vivax chloroquine resistance has been documented in nearly every region where this malaria-causing parasite is endemic. Unfortunately, P. vivax resistance surveillance and drug discovery are challenging due to the low parasitemias of patient isolates and poor parasite survival through ex vivo maturation that reduce the sensitivity and scalability of current P. vivax antimalarial assays. Using cryopreserved patient isolates from Brazil and fresh patient isolates from India, we established a robust enrichment method for P. vivax parasites. We next performed a medium screen for formulations that enhance ex vivo survival. Finally, we optimized an isotopic metabolic labeling assay for measuring P. vivax maturation and its sensitivity to antimalarials. A KCl Percoll density gradient enrichment method increased parasitemias from small-volume ex vivo isolates by an average of >40-fold. The use of Iscove's modified Dulbecco's medium for P. vivax ex vivo culture approximately doubled the parasite survival through maturation. Coupling these with [³H]hypoxanthine metabolic labeling permitted sensitive and robust measurements of parasite maturation, which was used to measure the sensitivities of Brazilian P. vivax isolates to chloroquine and several novel antimalarials. These techniques can be applied to rapidly and robustly assess the P. vivax isolate sensitivities to antimalarials for resistance surveillance and drug discovery.

SLCO1A2, SLCO1B1 and SLCO2B1 polymorphisms influences chloroquine and primaquine treatment in Plasmodium vivax malaria

AIM

The association of transporters gene polymorphisms with chloroquine/primaquine malaria treatment response was investigated in a Brazilian population.

PATIENTS & METHODS

Totally, 164 Plasmodium vivax malaria infected patients were included. Generalized estimating equations were performed to determine gene influences on parasitemia and/or gametocytemia clearance over treatment time.

RESULTS

Significant interaction between SLCO2B1 genotypes and treatment over time for parasitemia clearance rate on day 2 were observed (p FDR = 0.002). SLCO1A2 and SLCO1B1 gene treatment over time interactions were associated with gametocytemia clearance rate (p FDR = 0.018 and p FDR = 0.024). ABCB1, ABCC4 and SLCO1B3 were not associated with treatment response.

CONCLUSION

The present work presents the first pharmacogenetic report of an association between chloroquine/primaquine responses with OATP transporters.

Plasma metabolomics reveals membrane lipids, aspartate/asparagine and nucleotide metabolism pathway differences associated with chloroquine resistance in Plasmodium vivax malaria

Background

Chloroquine (CQ) is the main anti-schizontocidal drug used in the treatment of uncomplicated malaria caused by Plasmodium vivax. Chloroquine resistant P. vivax (PvCR) malaria in the Western Pacific region, Asia and in the Americas indicates a need for biomarkers of resistance to improve therapy and enhance understanding of the mechanisms associated with PvCR. In this study, we compared plasma metabolic profiles of P. vivax malaria patients with PvCR and chloroquine sensitive parasites before treatment to identify potential molecular markers of chloroquine resistance.

Methods

An untargeted high-resolution metabolomics analysis was performed on plasma samples collected in a malaria clinic in Manaus, Brazil. Male and female patients with Plasmodium vivax were included (n = 46); samples were collected before CQ treatment and followed for 28 days to determine PvCR, defined as the recurrence of parasitemia with detectable plasma concentrations of CQ ≥100 ng/dL. Differentially expressed metabolic features between CQ-Resistant (CQ-R) and CQ-Sensitive (CQ-S) patients were identified using partial least squares discriminant analysis and linear regression after adjusting for covariates and multiple testing correction. Pathway enrichment analysis was performed using Mummichog.

Results

Linear regression and PLS-DA methods yielded 69 discriminatory features between CQ-R and CQ-S groups, with 10-fold cross-validation classification accuracy of 89.6% using a SVM classifier. Pathway enrichment analysis showed significant enrichment (p<0.05) of glycerophospholipid metabolism, glycosphingolipid metabolism, aspartate and asparagine metabolism, purine and pyrimidine metabolism, and xenobiotics metabolism. Glycerophosphocholines levels were significantly lower in the CQ-R group as compared to CQ-S patients and also to independent control samples.

Conclusions

The results show differences in lipid, amino acids, and nucleotide metabolism pathways in the plasma of CQ-R versus CQ-S patients prior to antimalarial treatment. Metabolomics phenotyping of P. vivax samples from patients with well-defined clinical CQ-resistance is promising for the development of new tools to understand the biological process and to identify potential biomarkers of PvCR.

Population-level estimates of the proportion of Plasmodium vivax blood-stage infections attributable to relapses among febrile patients attending Adama Malaria Diagnostic Centre, East Shoa Zone, Oromia, Ethiopia

Background

Malaria is ranked as the leading communicable disease in Ethiopia, where Plasmodium falciparum and Plasmodium vivax are co-endemic. The incidence of P. vivax is usually considered to be less seasonal than P. falciparum. Clinical cases of symptomatic P. falciparum exhibit notable seasonal variation, driven by rainfall-dependent variation in the abundance of Anopheles mosquitoes. A similar peak of clinical cases of P. vivax is usually observed during the rainy season. However, the ability of P. vivax to relapse causing new blood-stage infections weeks to months after an infectious mosquito bite can lead to substantial differences in seasonal patterns of clinical cases. These cannot be detected with currently available diagnostic tools and are not cleared upon treatment with routinely administered anti-malarial drugs.

Methods

A health- facility based cross-sectional study was conducted in Adama malaria diagnostic centre from May 2015 to April 2016. Finger-prick blood samples were collected for thin and thick blood film preparation from participants seeking treatment for suspected cases of febrile malaria. Informed consent was obtained from each study participant or their guardians. Seasonal patterns in malaria cases were analysed using statistical models, identifying the peaks in cases, and the seasonally varying proportion of P. vivax cases attributable to relapses.

Results

The proportion of patients with malaria detectable by light microscopy was 36.1% (1141/3161) of which P. vivax, P. falciparum, and mixed infections accounted for 71.4, 25.8 and 2.8%, respectively. Of the febrile patients diagnosed, 2134 (67.5%) were males and 1919 (60.7%) were urban residents. The model identified a primary peak in P. falciparum and P. vivax cases from August to October, as well as a secondary peak of P. vivax cases from February to April attributable to cases arising from relapses. During the secondary peak of P. vivax cases approximately 77% (95% CrI 68, 84%) of cases are estimated to be attributable to relapses. During the primary peak from August to October, approximately 40% (95% CrI 29, 57%) of cases are estimated to be attributable to relapses.

Discussion

It is not possible to diagnose whether a P. vivax case has been caused by blood-stage infection from a mosquito bite or a relapse. However, differences in seasonal patterns of P. falciparum and P. vivax cases can be used to estimate the population-level proportion of P. vivax cases attributable to relapses. These observations have important implications for the epidemiological assessment of vivax malaria, and initiating therapy that is effective against both blood stages and relapses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1944-3) contains supplementary material, which is available to authorized users.

Chloroquine efficacy for Plasmodium vivax in Myanmar in populations with high genetic diversity and moderate parasite gene flow

BACKGROUND

Plasmodium vivax malaria remains a major public health burden in Myanmar. Resistance to chloroquine (CQ), the first-line treatment for P. vivax, has been reported in the country and has potential to undermine local control efforts.

METHODS

Patients over 6 years of age with uncomplicated P. vivax mono-infection were enrolled into clinical efficacy studies in Myawaddy in 2014 and Kawthoung in 2012. Study participants received a standard dose of CQ (25 mg/kg over 3 days) followed by weekly review until day 28. Pvmdr1 copy number (CN) and microsatellite diversity were assessed on samples from the patients enrolled in the clinical study and additional cross-sectional surveys undertaken in Myawaddy and Shwegyin in 2012.

RESULTS

A total of 85 patients were enrolled in the CQ clinical studies, 25 in Myawaddy and 60 in Kawthoung. One patient in Myawaddy (1.2%) had an early treatment failure and two patients (2.3%) in Kawthoung presented with late treatment failures on day 28. The day 28 efficacy was 92.0% (95% CI 71.6-97.9) in Myawaddy and 98.3% (95% CI 88.7-99.8) in Kawthoung. By day 2, 92.2% (23/25) in Myawaddy and 85.0% (51/60) in Kawthoung were aparasitaemic. Genotyping and pvmdr1 CN assessment was undertaken on 43, 52 and 46 clinical isolates from Myawaddy, Kawthoung and Shwegyin respectively. Pvmdr1 amplification was observed in 3.2% (1/31) of isolates in Myawaddy, 0% (0/49) in Kawthoung and 2.5% (1/40) in Shwegyin. Diversity was high in all sites (H _E 0.855-0.876), with low inter-population differentiation (F _ST 0.016-0.026, P < 0.05).

CONCLUSIONS

Treatment failures after chloroquine were observed following chloroquine monotherapy, with pvmdr1 amplification present in both Myawaddy and Shwegyin. The results emphasize the importance of ongoing P. vivax drug resistance surveillance in Myanmar, particularly given the potential connectivity between parasite population at different sites.

Comparison of artemether-lumefantrine and chloroquine with and without primaquine for the treatment of Plasmodium vivax infection in Ethiopia: A randomized controlled trial

BACKGROUND

Recent efforts in malaria control have resulted in great gains in reducing the burden of Plasmodium falciparum, but P. vivax has been more refractory. Its ability to form dormant liver stages confounds control and elimination efforts. To compare the efficacy and safety of primaquine regimens for radical cure, we undertook a randomized controlled trial in Ethiopia.

METHODS AND FINDINGS

Patients with normal glucose-6-phosphate dehydrogenase status with symptomatic P. vivax mono-infection were enrolled and randomly assigned to receive either chloroquine (CQ) or artemether-lumefantrine (AL), alone or in combination with 14 d of semi-supervised primaquine (PQ) (3.5 mg/kg total). A total of 398 patients (n = 104 in the CQ arm, n = 100 in the AL arm, n = 102 in the CQ+PQ arm, and n = 92 in the AL+PQ arm) were followed for 1 y, and recurrent episodes were treated with the same treatment allocated at enrolment. The primary endpoints were the risk of P. vivax recurrence at day 28 and at day 42. The risk of recurrent P. vivax infection at day 28 was 4.0% (95% CI 1.5%-10.4%) after CQ treatment and 0% (95% CI 0%-4.0%) after CQ+PQ. The corresponding risks were 12.0% (95% CI 6.8%-20.6%) following AL alone and 2.3% (95% CI 0.6%-9.0%) following AL+PQ. On day 42, the risk was 18.7% (95% CI 12.2%-28.0%) after CQ, 1.2% (95% CI 0.2%-8.0%) after CQ+PQ, 29.9% (95% CI 21.6%-40.5%) after AL, and 5.9% (95% CI 2.4%-13.5%) after AL+PQ (overall p < 0.001). In those not prescribed PQ, the risk of recurrence by day 42 appeared greater following AL treatment than CQ treatment (HR = 1.8 [95% CI 1.0-3.2]; p = 0.059). At the end of follow-up, the incidence rate of P. vivax was 2.2 episodes/person-year for patients treated with CQ compared to 0.4 for patients treated with CQ+PQ (rate ratio: 5.1 [95% CI 2.9-9.1]; p < 0.001) and 2.3 episodes/person-year for AL compared to 0.5 for AL+PQ (rate ratio: 6.4 [95% CI 3.6-11.3]; p < 0.001). There was no difference in the occurrence of adverse events between treatment arms. The main limitations of the study were the early termination of the trial and the omission of haemoglobin measurement after day 42, resulting in an inability to estimate the cumulative risk of anaemia.

CONCLUSIONS

Despite evidence of CQ-resistant P. vivax, the risk of recurrence in this study was greater following treatment with AL unless it was combined with a supervised course of PQ. PQ combined with either CQ or AL was well tolerated and reduced recurrence of vivax malaria by 5-fold at 1 y.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01680406.

Clinical and molecular surveillance of drug resistant vivax malaria in Myanmar (2009-2016)

BACKGROUND

One of the major challenges for control and elimination of malaria is ongoing spread and emergence of drug resistance. While epidemiology and surveillance of the drug resistance in falciparum malaria is being explored globally, there are few studies on drug resistance vivax malaria.

METHODS

To assess the spread of drug-resistant vivax malaria in Myanmar, a multisite, prospective, longitudinal study with retrospective analysis of previous therapeutic efficacy studies, was conducted. A total of 906 from nine study sites were included in retrospective analysis and 208 from three study sites in prospective study. Uncomplicated vivax mono-infected patients were recruited and monitored with longitudinal follow-up until day 28 after treatment with chloroquine. Amplification and sequence analysis of molecular markers, such as mutations in pvcrt-O, pvmdr1, pvdhps and pvdhfr, were done in day-0 samples in prospective study.

RESULTS

Clinical failure cases were found only in Kawthaung, southern Myanmar and western Myanmar sites within 2009-2016. Chloroquine resistance markers, pvcrt-O 'AAG' insertion and pvmdr1 mutation (Y976F) showed higher mutant rate in southern and central Myanmar than western site: 66.7, 72.7 vs 48.3% and 26.7, 17.0 vs 1.7%, respectively. A similar pattern of significantly higher mutant rate of antifolate resistance markers, pvdhps (S382A, K512M, A553G) and pvdhfr (F57L/I, S58R, T61M, S117T/N) were noted.

CONCLUSIONS

Although clinical failure rate was low, widespread distribution of chloroquine and antifolate resistance molecular makers alert to the emergence and spread of drug resistance vivax malaria in Myanmar. Proper strategy and action plan to eliminate and contain the resistant strain strengthened together with clinical and molecular surveillance on drug resistance vivax is recommended.

Diagnosis and Treatment of Plasmodium vivax Malaria

The diagnosis and treatment of Plasmodium vivax malaria differs from that of Plasmodium falciparum malaria in fundamentally important ways. This article reviews the guiding principles, practices, and evidence underpinning the diagnosis and treatment of P. vivax malaria.

Molecular Epidemiology of P. vivax in Iran: High Diversity and Complex Sub-Structure Using Neutral Markers, but No Evidence of Y976F Mutation at pvmdr1

BACKGROUND

Malaria remains endemic at low levels in the south-eastern provinces of Iran bordering Afghanistan and Pakistan, with the majority of cases attributable to P. vivax. The national guidelines recommend chloroquine (CQ) as blood-stage treatment for uncomplicated P. vivax, but the large influx of imported cases enhances the risk of introducing CQ resistance (CQR).

METHODOLOGY AND PRINCIPAL FINDINGS

The genetic diversity at pvmdr1, a putative modulator of CQR, and across nine putatively neutral short tandem repeat (STR) markers were assessed in P. vivax clinical isolates collected between April 2007 and January 2013 in Hormozgan Province, south-eastern Iran. One hundred blood samples were collected from patients with microscopy-confirmed P. vivax enrolled at one of five district clinics. In total 73 (73%) were autochthonous cases, 23 (23%) imported cases from Afghanistan or Pakistan, and 4 (4%) with unknown origin. 97% (97/100) isolates carried the F1076L mutation, but none carried the Y976F mutation. STR genotyping was successful in 71 (71%) isolates, including 57(57%) autochthonous and 11 (11%) imported cases. Analysis of population structure revealed 2 major sub-populations, K1 and K2, with further sub-structure within K2. The K1 sub-population had markedly lower diversity than K2 (HE = 0.06 vs HE = 0.82) suggesting that the sub-populations were sustained by distinct reservoirs with differing transmission dynamics, possibly reflecting local versus imported/introduced populations. No notable separation was observed between the local and imported cases although the sample size was limited.

CONCLUSIONS

The contrasting low versus high diversity in the two sub-populations (K1 and K2) infers that a combination of local transmission and cross-border malaria from higher transmission regions shape the genetic make-up of the P. vivax population in south-eastern Iran. There was no molecular evidence of CQR amongst the local or imported cases, but ongoing clinical surveillance is warranted.

Dissecting malaria biology and epidemiology using population genetics and genomics

Molecular approaches have an increasingly recognized utility in surveillance of malaria parasite populations, not only in defining prevalence and incidence with higher sensitivity than traditional methods, but also in monitoring local and regional parasite transmission patterns. In this review, we provide an overview of population genetic and genomic studies of human-infecting Plasmodium species, highlighting recent advances in the field. In accordance with the renewed impetus for malaria eradication, many studies are now using genetic and genomic epidemiology to support local evidence-based intervention strategies. Microsatellite genotyping remains a popular approach for both Plasmodium falciparum and Plasmodium vivax. However, with the increasing availability of whole genome sequencing data enabling effective single nucleotide polymorphism-based panels tailored to a given study question and setting, this approach is gaining popularity. The availability of new reference genomes for Plasmodium malariae and Plasmodium ovale should see a surge in similar molecular studies on these currently neglected species. Genomic studies are revealing new insights into important adaptive mechanisms of the parasite including antimalarial drug resistance. The advent of new methodologies such as selective whole genome amplification for dealing with extensive human DNA in low density field isolates should see genome-wide approaches becoming routine for parasite surveillance once the economic costs outweigh the current cost benefits of targeted approaches.

Genomic Analysis Reveals a Common Breakpoint in Amplifications of the Plasmodium vivax Multidrug Resistance 1 Locus in Thailand

In regions of coendemicity for Plasmodium falciparum and Plasmodium vivax where mefloquine is used to treat P. falciparum infection, drug pressure mediated by increased copy numbers of the multidrug resistance 1 gene (pvmdr1) may select for mefloquine-resistant P. vivax Surveillance is not undertaken routinely owing in part to methodological challenges in detection of gene amplification. Using genomic data on 88 P. vivax samples from western Thailand, we identified pvmdr1 amplification in 17 isolates, all exhibiting tandem copies of a 37.6-kilobase pair region with identical breakpoints. A novel breakpoint-specific polymerase chain reaction assay was designed to detect the amplification. The assay demonstrated high sensitivity, identifying amplifications in 13 additional, polyclonal infections. Application to 132 further samples identified the common breakpoint in all years tested (2003-2015), with a decline in prevalence after 2012 corresponding to local discontinuation of mefloquine regimens. Assessment of the structure of pvmdr1 amplification in other geographic regions will yield information about the population-specificity of the breakpoints and underlying amplification mechanisms.

Efficacy of Artesunate-mefloquine for Chloroquine-resistant Plasmodium vivax Malaria in Malaysia: An Open-label, Randomized, Controlled Trial

BACKGROUND

Chloroquine (CQ)-resistant Plasmodium vivax is increasingly reported throughout southeast Asia. The efficacy of CQ and alternative artemisinin combination therapies (ACTs) for vivax malaria in Malaysia is unknown.

METHODS

A randomized, controlled trial of CQ vs artesunate-mefloquine (AS-MQ) for uncomplicated vivax malaria was conducted in 3 district hospitals in Sabah, Malaysia. Primaquine was administered on day 28. The primary outcome was the cumulative risk of treatment failure by day 28 by Kaplan-Meier analysis.

RESULTS

From 2012 to 2014, 103 adults and children were enrolled. Treatment failure by day 28 was 61.1% (95% confidence interval [CI], 46.8-75.6) after CQ and 0% (95% CI, 0-.08) following AS-MQ (P < .001), of which 8.2% (95% CI, 2.5-9.6) were early treatment failures. All patients with treatment failure had therapeutic plasma CQ concentrations at day 7. Compared with CQ, AS-MQ was associated with faster parasite clearance (normalized clearance slope, 0.311 vs 0.127; P < .001) and fever clearance (mean, 19.0 vs 37.7 hours; P =001) and with lower risk of anemia at day 28 (odds ratio = 3.7; 95% CI, 1.5-9.3; P =005). Gametocytes were present at day 28 in 23.8% (10/42) of patients following CQ vs none with AS-MQ (P < .001). AS-MQ resulted in lower bed occupancy: 4037 vs 6510 days/1000 patients (incidence rate ratio 0.62; 95% CI, .60-.65; P < .001). One patient developed severe anemia not regarded as related to their AS-MQ treatment.

CONCLUSIONS

High-grade CQ-resistant P. vivax is prevalent in eastern Malaysia. AS-MQ is an efficacious ACT for all malaria species. Wider CQ-efficacy surveillance is needed in vivax-endemic regions with earlier replacement with ACT when treatment failure is detected.Clinical Trials Registration NCT01708876.

Targeting vivax malaria in the Asia Pacific: The Asia Pacific Malaria Elimination Network Vivax Working Group

The Asia Pacific Malaria Elimination Network (APMEN) is a collaboration of 18 country partners committed to eliminating malaria from within their borders. Over the past 5 years, APMEN has helped to build the knowledge, tools and in-country technical expertise required to attain this goal. At its inaugural meeting in Brisbane in 2009, Plasmodium vivax infections were identified across the region as a common threat to this ambitious programme; the APMEN Vivax Working Group was established to tackle specifically this issue. The Working Group developed a four-stage strategy to identify knowledge gaps, build regional consensus on shared priorities, generate evidence and change practice to optimize malaria elimination activities. This case study describes the issues faced and the solutions found in developing this robust strategic partnership between national programmes and research partners within the Working Group. The success of the approach adopted by the group may facilitate similar applications in other regions seeking to deploy evidence-based policy and practice.