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

Surveillance of drug resistance molecular markers in Plasmodium vivax before and after introduction of dihydroartemisinin and piperaquine in Thailand: 2009-2019

Resistance to antimalarial drugs is a serious issue around the world. Widespread Plasmodium vivax and P. falciparum coinfections are commonly found in Thailand. Dihydroartemisinin and piperaquine (DHA-PPQ) have been used as first-line treatments for P. falciparum since 2015, and chloroquine (CQ) and primaquine (PQ) have remained first-line drugs for P. vivax for more than 60 years. Coinfections may lead parasites to evolve with regard to genetics under selective drug pressure. This study is aimed at investigating genes linked to antimalarial resistance in P. vivax before and after introduction of DHA-PPQ as a new drug regimen in Thailand. A total of 400 P. vivax isolates were collected from samples along the Thai-Myanmar and Thai-Malaysian borders before (2009-2015) and after (2016-2019) introduction of DHA-PPQ. Genomic DNA of P. vivax was obtained and subjected to analysis of five drug resistance-associated genes (Pvdhfr, Pvdhps, Pvmdr1, Pvcrt-o, and PvK12) by nested polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP), and nucleotide sequencing. A high prevalence of Pvdhfr was found in both endemic areas over the period. The quadruple (57I/58R/61M/117T) Pvdhfr haplotype was predominant in both periods in both endemic areas. Although the wild-type haplotype of Pvdhps was predominant in Thai-Malaysian isolates in both periods, a single mutant haplotype (383G) was dominant in Thai-Myanmar isolates during both periods. A low prevalence of the Pvmdr1 976F mutation was found in both periods among Thai-Myanmar isolates. A significant decrease in Pvmdr1 976F was identified in Thai-Malaysian isolates from the second period (p < 0.01). Only one nonsynonymous mutation of Pvcrt-o (193E) and one synonymous mutation of PvK12 (R584) were detected in four isolates (4.7%) and one isolate (0.5%) in the first period among Thai-Myanmar isolates, respectively. Thus, with limited clinical efficacy data, the low prevalence of drug-resistance markers may suggest that there is a low prevalence of P. vivax-resistant strains and that the current drug regimen for P. vivax is still effective for treating this P. vivax parasite population. Continued surveillance of antimalarial drug resistance markers and monitoring of clinical drug efficacy should be conducted for epidemiological and policy implications.

Molecular surveillance of chloroquine resistance in Plasmodium vivax isolates from malaria cases in Yunnan Province of China using pvcrt-o gene polymorphisms

BACKGROUND

The efficacy of chloroquine treatment for vivax malaria has been rarely evaluated due to a lack of an appropriate testing method. The objective of this study was to conduct molecular monitoring of chloroquine resistance in Plasmodium vivax strains from vivax malaria patients in Yunnan Province, focusing on the analysis of polymorphism in the P. vivax chloroquine resistance transporter protein orthologous gene (pvcrt-o).

METHODS

In accordance with the principles of a cohort study, blood samples were collected from malaria cases diagnosed with a P. vivax mono-infection in Yunnan Province from 2020 to 2022. Segmental PCR was used to amplify the whole pvcrt-o gene in the blood samples and their products were subsequently sequenced. The sequencing data were arranged to obtain the full coding DNA sequence (CDS) as well as the gene's promoter region sequences. The CDSs were aligned with the reference sequence (XM_001613407.1) of the P. vivax SalI isolate to identify the mutant loci.

RESULTS

From a total of 375 blood samples taken from vivax malaria cases, 272 both whole gene CDSs (1272-1275 bp) and promoter DNA sequences (707 bp) of pvcrt-o gene were obtained. Among the whole CDSs, there were 7 single nucleotide polymorphic sites in which c.7 A>G was the minor allele frequency (MAF) site with 4.4% (12/272) detection rate. The mutation detection rate showed a significant decrease from 9.8% (10/102) in 2020 to 1.1% (1/92) in 2021 and 1.3% (1/78) in 2022, indicating statistical significance (χ2 = 11.256, P < 0.05). Among the identified 12 haplotypes, the majority of which were wild type (75.7%; 206/272). These four mutant haplotypes (Hap_3, Hap_5, Hap_9, and Hap_10) were classified as "K10 insertion type" and accounted for 12.1% (33/272). The detection rate of Hap_3 increased from 1.0% (1/102) in 2020 to 13.0% (12/92) in 2021 and 14.1% (11/78) in 2022, indicating statistical significance. A total of 23.8% (65/272) of the samples exhibited 14 bp (bp) deletions in the promoter region, occurring most frequently in the wild type haplotype (Hap_1) samples at a rate of 28.6% (59/206).

CONCLUSIONS

In recent years in Yunnan Province, a notable proportion of vivax malaria patients are infected by P. vivax strains with a "K10 insertion" and partial sequence deletions in the promoter region of the pvcrt-o gene, necessitating vigilance.

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.

A review of malaria molecular markers for drug resistance in Plasmodium falciparum and Plasmodium vivax in China

China has now achieved the elimination of malaria, but it still faces severe challenges in the post-elimination stage. China continues to be plagued by imported malaria cases, and preventing re-transmission of imported malaria is critical. The effectiveness of antimalarial drugs for malaria control largely depends on the study of drug resistance markers in vitro. Monitoring molecular markers of parasite-associated drug resistance can help predict and manage drug resistance. There is currently a lack of systematic reviews of molecular markers for indigenous and imported malaria in China. Therefore, this review summarizes the published articles related to molecular marker polymorphism of indigenous and imported malaria cases in China in the past two decades, to study the mutation frequency and distribution of crt, mdr1, dhps, dhfr and K13 gene resistance-related loci. This can provide a whole picture of molecular markers and the resistance mutations of imported cases in China, which has certain significance for drug resistance surveillance planning, safe and effective treatment, and preventing the recurrence of local transmission by imported malaria in China in the future.

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.

Molecular Profiles of Multiple Antimalarial Drug Resistance Markers in Plasmodium falciparum and Plasmodium vivax in the Mandalay Region, Myanmar

Emergence and spreading of antimalarial drug resistant malaria parasites are great hurdles to combating malaria. Although approaches to investigate antimalarial drug resistance status in Myanmar malaria parasites have been made, more expanded studies are necessary to understand the nationwide aspect of antimalarial drug resistance. In the present study, molecular epidemiological analysis for antimalarial drug resistance genes in Plasmodium falciparum and P. vivax from the Mandalay region of Myanmar was performed. Blood samples were collected from patients infected with P. falciparum and P. vivax in four townships around the Mandalay region, Myanmar in 2015. Partial regions flanking major mutations in 11 antimalarial drug resistance genes, including seven genes (pfdhfr, pfdhps, pfmdr-1, pfcrt, pfk13, pfubp-1, and pfcytb) of P. falciparum and four genes (pvdhfr, pvdhps, pvmdr-1, and pvk12) of P. vivax were amplified, sequenced, and overall mutation patterns in these genes were analyzed. Substantial levels of mutations conferring antimalarial drug resistance were detected in both P. falciparum and P. vivax isolated in Mandalay region of Myanmar. Mutations associated with sulfadoxine-pyrimethamine resistance were found in pfdhfr, pfdhps, pvdhfr, and pvdhps of Myanmar P. falciparum and P. vivax with very high frequencies up to 90%. High or moderate levels of mutations were detected in genes such as pfmdr-1, pfcrt, and pvmdr-1 associated with chloroquine resistance. Meanwhile, low frequency mutations or none were found in pfk13, pfubp-1, pfcytb, and pvk12 of the parasites. Overall molecular profiles for antimalarial drug resistance genes in malaria parasites in the Mandalay region suggest that parasite populations in the region have substantial levels of mutations conferring antimalarial drug resistance. Continuous monitoring of mutations linked with antimalarial drug resistance is necessary to provide useful information for policymakers to plan for proper antimalarial drug regimens to control and eliminate malaria in the country.

Polymorphisms of potential drug resistant molecular markers in Plasmodium vivax from China–Myanmar border during 2008‒2017

Background

Plasmodium vivax remains the predominant species at the China–Myanmar border, imposing a major challenge to the recent gains in regional malaria elimination. To closely supervise the emerging of drug resistance in this area, we surveyed the variations in genes potentially correlated with drug resistance in P. vivax parasite and the possible drug selection with time.

Methods

A total of 235 P. vivax samples were collected from patients suffering uncomplicated malaria at Yingjiang, Tengchong, and Longling counties, and Nabang port in China, Yunnan province, and Laiza sub-township in Myanmar, from 2008 to 2017. Five potential drug resistance genes were amplified utilizing nested-PCR and analyzed, including pvdhfr, pvdhps, pvmdr1, pvcrt-o, and pvk12. The Pearson’s Chi-squared test or Fisher’s exact test were applied to determine the statistical frequency differences of mutations between categorical data.

Results

The pvdhfr F57I/L, S58R, T61M and S117T/N presented in 40.6%, 56.7%, 40.1%, and 56.0% of the sequenced P. vivax isolates, and these mutations significantly decreased with years. The haplotype formed by these quadruple mutations predominated in Yingjiang, Tengchong, Longling and Nabang. While a mutation H99S/R (56.6%) dominated in Laiza and increased with time. In pvdhps, the A383G prevailed in 69.2% of the samples, which remained the most prevalent haplotype. However, a significant decrease of its occurrence was also noticed over the time. The S382A/C and A553G existed in 8.4% and 30.8% of the isolates, respectively. In pvmdr1, the mutation Y976F occurred at a low frequency in 5/232 (2.2%), while T958M was fixed and F1076L was approaching fixed (72.4%). The K10 insertion was detected at an occurrence of 33.2% in pvcrt-o, whereas there was no significant difference among the sites or over the time. No mutation was identified in pvk12.

Conclusions

Mutations related with resistance to antifolate drugs are prevalent in this area, while their frequencies decrease significantly with time, suggestive of increased susceptibility of P. vivax parasite to antifolate drugs. Resistance to chloroquine (CQ) is possibly emerging. However, since the molecular mechanisms underneath CQ resistance is yet to be better understood, close supervision of clinical drug efficiency and continuous function investigation is urgently needed to alarm drug resistance.

Graphical abstract

Genetic polymorphisms in genes associated with drug resistance in Plasmodium vivax parasites from northeastern Myanmar

Background

Anti-malarial drug resistance is still a major threat to malaria elimination in the Great Mekong Sub-region. Plasmodium vivax parasites resistant to anti-malarial drugs are now found in Myanmar. Molecular surveillance on drug resistance genes in P. vivax parasites from northeastern Myanmar was aimed at estimating the underlying drug resistance in this region.

Methods

Blood samples from patients with vivax malaria were collected from Laiza city in northeastern Myanmar in 2020. Drug resistance genes including Pvcrt-o, Pvmdr1, Pvdhfr and Pvdhps were amplified and sequenced. Genetic polymorphisms and haplotypes were analysed to evaluate the prevalence of mutant alleles associated with drug resistance.

Results

A total of 149 blood samples from P. vivax patients were collected. The prevalence of Pvmdr1 mutations at codons 958 and 1076 was 100.0% and 52.0%, respectively, whereas no single nucleotide polymorphism was present at codon 976. The proportions of single and double mutant types were 48.0% and 52.0%, respectively. A K10 “AAG” insertion in the Pvcrt-o gene was not detected. Mutations in Pvdhfr at codons 57, 58, 61, 99 and 117 were detected in 29.9%, 54.3%, 27.6%, 44.9% and 55.1% of the samples, respectively. Wild type was predominant (46.3%), followed by quadruple and double mutant haplotypes. Of three types of tandem repeat variations of Pvdhfr, Type B, with three copies of GGDN repeats, was the most common. Pvdhps mutations were only detected at codons 383 and 553 and the wild type Pvdhps was dominant (78.0%). Eleven haplotypes were identified when combining the mutations of Pvdhfr and Pvdhps, among which the predominant one was the wild type (33.9%), followed by double mutant alleles S58R/S117N /WT (24.6%).

Conclusions

This study demonstrated resistant P. vivax phenotypes exists in northeastern Myanmar. Continued surveillance of drug resistance markers is needed to update treatment guidelines in this region.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04084-y.

Therapeutic efficacy of chloroquine for uncomplicated Plasmodium vivax malaria in southeastern and western border areas of Myanmar

BACKGROUND

In the Greater Mekong Subregion of Southeast Asia, Plasmodium vivax malaria is endemic and causes significant morbidity. In this study, the efficacy of chloroquine for treating uncomplicated P. vivax malaria at the eastern and western borders of Myanmar was investigated.

METHODS

A total of 197 participants with microscopically confirmed P. vivax infection were enrolled from three townships of the southeastern (Thanbyuzayat and Kawthoung) and western (Kyauktaw) borders of Myanmar. Patients were treated with chloroquine according to the national malaria treatment guidelines and followed for 28 days.

RESULTS

Among the 197 enrollments, 172 completed the 28-day follow-up. Twelve recurrent P. vivax infections, all occurring in the third and fourth week, were detected, resulting in an overall cumulative rate of recurrence of 4.7% [95% confidence interval (CI) 1.5-7.8]. The incidence rate of recurrence varied among the three sites. In Thanbyuzayat township, no patients had recurrent parasitemia between days 7 and 28. In contrast, Kyauktaw township had a day 28 cumulative incidence rate of recurrence of 7.2% (95% CI 0.6-13.9%) compared to 6.9% (95% CI 0.6-13.2) in Kawthoung township.

CONCLUSION

While this study confirmed the relatively high clinical efficacy of chloroquine for treating P. vivax in Myanmar with modest rates of recurrent infections within 28 days of the treatment, it also revealed considerable geographical heterogeneity of chloroquine efficacy, which warrants continuous surveillance efforts.

Molecular Surveillance and Ex Vivo Drug Susceptibilities of Plasmodium vivax Isolates From the China-Myanmar Border

Drug resistance in Plasmodium vivax may pose a challenge to malaria elimination. Previous studies have found that P. vivax has a decreased sensitivity to antimalarial drugs in some areas of the Greater Mekong Sub-region. This study aims to investigate the ex vivo drug susceptibilities of P. vivax isolates from the China–Myanmar border and genetic variations of resistance-related genes. A total of 46 P. vivax clinical isolates were assessed for ex vivo susceptibility to seven antimalarial drugs using the schizont maturation assay. The medians of IC₅₀ (half-maximum inhibitory concentrations) for chloroquine, artesunate, and dihydroartemisinin from 46 parasite isolates were 96.48, 1.95, and 1.63 nM, respectively, while the medians of IC₅₀ values for piperaquine, pyronaridine, mefloquine, and quinine from 39 parasite isolates were 19.60, 15.53, 16.38, and 26.04 nM, respectively. Sequence polymorphisms in pvmdr1 (P. vivax multidrug resistance-1), pvmrp1 (P. vivax multidrug resistance protein 1), pvdhfr (P. vivax dihydrofolate reductase), and pvdhps (P. vivax dihydropteroate synthase) were determined by PCR and sequencing. Pvmdr1 had 13 non-synonymous substitutions, of which, T908S and T958M were fixed, G698S (97.8%) and F1076L (93.5%) were highly prevalent, and other substitutions had relatively low prevalences. Pvmrp1 had three non-synonymous substitutions, with Y1393D being fixed, G1419A approaching fixation (97.8%), and V1478I being rare (2.2%). Several pvdhfr and pvdhps mutations were relatively frequent in the studied parasite population. The pvmdr1 G698S substitution was associated with a reduced sensitivity to chloroquine, artesunate, and dihydroartemisinin. This study suggests the possible emergence of P. vivax isolates resistant to certain antimalarial drugs at the China–Myanmar border, which demands continuous surveillance for drug resistance.

Limited polymorphism in k13 gene of Plasmodium falciparum and k12 of Plasmodium vivax isolates imported from African and Asian countries between 2014 and 2019 in Hangzhou city, China

Background

Malaria causes major public health problems globally and drug resistance hinders its control and elimination. Molecular markers associated with drug resistance are considered as a beneficial tool to monitor the disease trends, evolution and distribution so as to help improve drug policy.

Methods

We collected 148 Plasmodium falciparum and 20 Plasmodium vivax isolates imported into Hangzhou city, China between 2014 and 2019. k13 gene of P. falciparum and k12 of P. vivax were sequenced. Polymorphisms and prevalence of k13 and k12 were analyzed.

Results

Most (98.65%, 146/148) P. falciparum infections were imported from Africa, and half P. vivax cases came from Africa and the other half from Asia. Nucleotide mutation prevalence was 2.03% (3/148) and the proportion of amino acid mutations was 0.68% (1/148). The amino acid mutation, A676S, was observed in an isolate from Nigeria. No mutation of k12 was observed from the parasites from African and Asian countries.

Conclusions

Limited polymorphism in k13 gene of P. falciparum isolates imported from African countries, but no evidence for the polymorphism of k12 in P. vivax samples from African and Asian countries was found. These results provide information for drug policy update in study region.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06579-6.

The molecular basis of antimalarial drug resistance in Plasmodium vivax

Plasmodium vivax is the most geographically widespread cause of human malaria and is responsible for the majority of cases outside of the African continent. While great progress has been made towards eliminating human malaria, drug resistant parasite strains pose a threat towards continued progress. Resistance has arisen to multiple antimalarials in P. vivax, including to chloroquine, which is currently the first line therapy for P. vivax in most regions. Despite its importance, an understanding of the molecular mechanisms of drug resistance in this species remains elusive, in large part due to the complex biology of P. vivax and the lack of in vitro culture. In this review, we will cover the extent and challenges of measuring clinical and in vitro drug resistance in P. vivax. We will consider the roles of candidate drug resistance genes. We will highlight the development of molecular approaches for studying P. vivax biology that provide the opportunity to validate the role of putative drug resistance mutations as well as identify novel mechanisms of drug resistance in this understudied parasite. Validated molecular determinants and markers of drug resistance are essential for the rapid and cost-effective monitoring of drug resistance in P. vivax, and will be useful for optimizing drug regimens and for informing drug policy in control and elimination settings.

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Drug resistance is emerging in Plasmodium vivax, an important cause of malaria.

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The complex biology of P. vivax and the limited range of research tools make it difficult to identify drug resistance.

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The molecular mechanisms of drug resistance in P. vivax remain elusive.

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This review highlights the extent of drug resistance, the putative mechanisms of resistance and new technologies for the study of P. vivax drug resistance.

Efficacy and Safety of Pyronaridine-Artesunate for the Treatment of Uncomplicated Plasmodium falciparum and Plasmodium vivax Malaria in Myanmar

Four single-arm, prospective, clinical studies of pyronaridine–artesunate efficacy in uncomplicated Plasmodium falciparum or Plasmodium vivax malaria were conducted in Myanmar between 2017 and 2019. Eligible subjects were aged at least 6 years, with microscopically confirmed P. falciparum (n = 196) or P. vivax mono-infection (n = 206). Patients received pyronaridine–artesunate once daily for 3 days with follow-up until day 42 for P. falciparum or day 28 for P. vivax. For the primary efficacy analysis, adequate clinical and parasitological response (ACPR) in the per-protocol population at day 42 for P. falciparum malaria was 100% (88/88; 95% CI: 95.9, 100) in northern Myanmar (Kachin State and northern Shan State), and 100% (101/101; 95% CI: 96.4, 100) in southern Myanmar (Tanintharyi Region and Kayin State). Plasmodium falciparum day-3 parasite clearance was observed for 96.9% (190/196) of patients. Mutations in the P. falciparum Kelch propeller domain (K13) were detected in 39.0% (69/177) of isolates: F446I (14.7% [26/177]), R561H (13.0% [23/177]), C580Y (10.2% [18/177]), and P574L (1.1% [2/177]). For P. vivax, the day-28 ACPR was 100% (104/104; 95% CI: 96.5, 100) in northern Myanmar and 100% (97/97; 95% CI: 96.3, 100) in southern Myanmar. Across both P. vivax studies, 100% (206/206) of patients had day-3 parasite clearance. There were no adverse events. Pyronaridine–artesunate had excellent efficacy in Myanmar against P. falciparum and P. vivax and was well tolerated. This study supports the inclusion of pyronaridine–artesunate in national malaria treatment guidelines for Myanmar.

Distribution pattern of amino acid mutations in chloroquine and antifolate drug resistance associated genes in complicated and uncomplicated Plasmodium vivax isolates from Chandigarh, North India

BACKGROUND

The increasing antimalarial drug resistance is a significant hindrance to malaria control and elimination programs. For the last six decades, chloroquine (CQ) plus pyrimethamine remains the first-line treatment for P. vivax malaria. Regions where both P. falciparum and P. vivax co-exist, P. vivax is exposed to antifolate drugs due to either misdiagnosis or improper treatment that causes selective drug pressure to evolve. Therefore, the present study aims to estimate antimalarial drug resistance among the complicated and uncomplicated P. vivax patients.

METHODS

A total of 143 P. vivax malaria positive patients were enrolled in this study, and DNA was isolated from their blood samples. Pvcrt-o, Pvmdr-1, Pvdhps, and Pvdhfr genes were PCRs amplified, and drug resistance-associated gene mutations were analyzed. Statistical analysis of the drug resistance genes and population diversity was performed using MEGA vs. 7.0.21 and DnaSP v software.

RESULTS

Among the CQ resistance marker gene Pvcrt-o, the prevalence of K10 insertion was 17.5% (7/40) and 9.5% (7/73) of complicated and uncomplicated P vivax group isolates respectively. In Pvmdr-1, double mutant haplotype (M₉₅₈/L₁₀₇₆) was found in 99% of the clinical isolates. Among the pyrimethamine resistance-associated gene Pvdhfr, the double mutant haplotype I₁₃P₃₃F₅₇R₅₈T₆₁N₁₁₇I₁₇₃ was detected in 23% (11/48) in complicated and 20% (17/85) in uncomplicated group isolates. In the sulphadoxine resistance-associated Pvdhps gene, limited polymorphism was observed with the presence of a single mutant (D459A) among 16 and 5% of the clinical isolates in the complicated and uncomplicated group respectively.

CONCLUSION

The study presents the situations of polymorphism in the antimalarial drug resistance-associated genes and emphasizes the need for regular surveillance. It is imperative for the development of suitable antimalarial drug policy in India.

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.

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.

Prevalence of molecular markers associated with drug resistance of Plasmodium vivax isolates in Western Yunnan Province, China

BACKGROUND

Plasmodium vivax is the most widely distributed malaria parasite, and its drug resistance poses unique challenges to malaria elimination. The Greater Mekong Subregion (GMS) is known as the global epicenter of multidrug resistance. Surveillance of molecular markers associated with drug resistance in this area will help to inform drug policy.

METHODS

Dry blood spots from 58 patients out of 109 with P. vivax infection between 2017, December and 2019, March were obtained from Yingjiang County, Yunnan Province, along the China-Myanmar border. Pvdhfr, Pvdhps, Pvmdr1 and Pvcrt-o were amplified and sequenced to assess gene mutations. The polymorphism and prevalence of these molecular markers were analyzed.

RESULTS

Mutations in Pvdhfr at codons 57, 58, 61, 99 and 117 were detected in 27.59, 48.28, 27.59, 32.76 and 48.28% of the isolates, respectively. Single mutant haplotype (I13F57S58T61S99S117I173) was the most frequent (29.31%, 17/58), followed by double mutant haplotype (20.69%, 12/58). Of three types of tandem repeat variations of Pvdhfr, deletion type was the most common. Pvdhps showed a lower prevalence among mutation genotypes. Single mutant was dominant and accounted for 34.48% (20/58). Prevalence of Pvmdr1 mutations at codons 958 and 1076 were 100.00% and 84.48%, respectively. The proportion of double and single mutant types was 84.48% (49/58) and 15.52% (9/58), respectively. Eleven samples (18.97%, 11/58) showed K10 "AAG" insertion in chloroquine resistance transporter gene Pvcrt-o.

CONCLUSIONS

There was moderate diversity of molecular patterns of resistance markers of Pvdhfr, Pvdhps, Pvmdr1 and Pvcrt-o in imported P. vivax cases to Yingjiang county in Western Yunnan, along the China-Myanmar border. Prevalence and molecular pattern of candidate drug resistance markers Pvdhfr, Pvdhps, Pvmdr1 and Pvcrt-o were demonstrated in this current study, which would help to update drug policy.

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.

Genetic diversity, natural selection and haplotype grouping of Plasmodium vivax Duffy-binding protein genes from eastern and western Myanmar borders

Background

Merozoite proteins of the malaria parasites involved in the invasion of red blood cells are selected by host immunity and their diversity is greatly influenced by changes in malaria epidemiology. In the Greater Mekong Subregion (GMS), malaria transmission is concentrated along the international borders and there have been major changes in malaria epidemiology with Plasmodium vivax becoming the dominant species in many regions. Here, we aimed to evaluate the genetic diversity of P. vivax Duffy-binding protein gene domain II (pvdbp-II) in isolates from the eastern and western borders of Myanmar, and compared it with that from global P. vivax populations.

Methods

pvdbp-II sequences were obtained from 85 and 82 clinical P. vivax isolates from the eastern and western Myanmar borders, respectively. In addition, 504 pvdbp-II sequences from nine P. vivax populations of the world were retrieved from GenBank and used for comparative analysis of genetic diversity, recombination and population structure of the parasite population.

Results

The nucleotide diversity of the pvdbp-II sequences from the Myanmar border parasite isolates was not uniform, with the highest diversity located between nucleotides 1078 and 1332. Western Myanmar isolates had a unique R391C mutation. Evidence of positive natural selection was detected in pvdbp-II gene in P. vivax isolates from the eastern Myanmar area. P. vivax parasite populations in the GMS, including those from the eastern, western, and central Myanmar as well as Thailand showed low-level genetic differentiation (F_ST, 0.000–0.099). Population genetic structure analysis of the pvdbp-II sequences showed a division of the GMS populations into four genetic clusters. A total of 60 PvDBP-II haplotypes were identified in 210 sequences from the GMS populations. Among the epitopes in PvDBP-II, high genetic diversity was found in epitopes 45 (379-SIFGT(D/G)(E/K)(K/N)AQQ(R/H)(R/C)KQ-393, π = 0.029) and Ia (416-G(N/K)F(I/M)WICK(L/I)-424], Ib [482-KSYD(Q/E)WITR-490, π = 0.028) in P. vivax populations from the eastern and western borders of Myanmar.

Conclusions

The pvdbp-II gene is genetically diverse in the eastern and western Myanmar border P. vivax populations. Positive natural selection and recombination occurred in pvdbp-II gene. Low-level genetic differentiation was identified, suggesting extensive gene flow of the P. vivax populations in the GMS. These results can help understand the evolution of the P. vivax populations in the course of regional malaria elimination and guide the design of PvDBP-II-based vaccine.

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.

Characterization of Plasmodium vivax pvmdr1 Polymorphisms in Isolates from Mangaluru, India

India accounts for approximately half of the global Plasmodium vivax cases, but information as to the presence of chloroquine (CQ) resistance is scarce. In an observational study in Mangaluru, south-western India, of 116 vivax malaria patients analyzed, 89.5% (102/114) had cleared parasitemia on days two or three of CQ treatment. Two remaining patients presented on days four and five without parasitemia. One hundred eight isolates of these 116 patients were successfully sequenced for pvmdr1 polymorphisms. Eight non-synonymous polymorphisms but no wild-type isolate were detected. Ten pvmdr1 haplotypes were observed with mutations T958M and F1076L occurring in all isolates, whereas the candidate CQ resistance marker Y976F was present in one isolate only. Pvmdr1 polymorphisms were not associated with early parasite clearance. The high proportion of early parasite clearance and the virtual absence of pvmdr1 Y976F and of sextuple pvmdr1 mutants suggest that CQ in the study area is still sufficiently effective. However, the abundance of pvmdr1 mutations in the local parasite population warrants monitoring.

Assessment of drug resistance associated genetic diversity in Mauritanian isolates of Plasmodium vivax reveals limited polymorphism

Background

Plasmodium vivax is the predominant malaria species in northern Mauritania. Molecular data on P. vivax isolates circulating in West Africa are scarce. The present study analysed molecular markers associated with resistance to antifolates (Pvdhfr and Pvdhps), chloroquine (Pvmdr1), and artemisinin (Pvk12) in P. vivax isolates collected in two cities located in the Saharan zone of Mauritania.

Methods

Blood samples were obtained from P. vivax-infected patients recruited for chloroquine therapeutic efficacy study in 2013 and febrile patients spontaneously consulting health facilities in Nouakchott and Atar in 2015–2016. Fragments of Pvdhfr (codons 13, 33, 57, 58, 61, 117, and 174), Pvdhps (codons 382, 383, 512, 553, and 585), Pvmdr1 (codons 976 and 1076) and Pvk12 (codon 552) genes were amplified by PCR and sequenced.

Results

Most of the isolates in Nouakchott (126/154, 81.8%) and Atar (44/45, 97.8%) carried the wild-type Pvdhfr allelic variant (IPFSTSI). In Nouakchott, all mutants (28/154; 18.2%) had double Pvdhfr mutations in positions 58 and 61 (allelic variant IPFRMSI), whereas in Atar only 1 isolate was mutant (S117N, allelic variant IPFSTNI). The wild-type Pvdhps allelic variant (SAKAV) was found in all tested isolates (Nouakchott, n = 93; Atar, n = 37). Few isolates in Nouakchott (5/115, 4.3%) and Atar (3/79, 3.8%) had the mutant Pvmdr1 allele 976F or 1076L, but not both, including in pre-treatment isolates obtained from patients treated successfully with chloroquine. All isolates (59 in Nouakchott and 48 in Atar) carried the wild-type V552 allele in Pvk12.

Conclusions

Polymorphisms in Pvdhfr, Pvdhps, Pvmdr1, and Pvk12 were limited in P. vivax isolates collected recently in Nouakchott and Atar. Compared to the isolates collected in Nouakchott in 2007–2009, there was no evidence for selection of mutants. The presence of one, but not both, of the two potential markers of chloroquine resistance in Pvmdr1 in pre-treatment isolates did not influence the clinical outcome, putting into question the role of Pvmdr1 mutant alleles 976F and 1076L in treatment failure. Molecular surveillance is an important component of P. vivax malaria control programme in the Saharan zone of Mauritania to predict possible emergence of drug-resistant parasites.

Chloroquine resistance is associated to multi-copy pvcrt-o gene in Plasmodium vivax malaria in the Brazilian Amazon

Background

The resistance of Plasmodium vivax to chloroquine has become an obstacle to control strategies based on the use of anti-malarials. The current study investigated the association between P. vivax CQ-resistance in vivo with copy number variation and mutations in the promoter region in pvcrt-o and pvmdr1 genes.

Methods

The study included patients with P. vivax that received supervised treatment with chloroquine and primaquine. Recurrences were actively recorded during this period.

Results

Among the 60 patients with P. vivax, 25 were CQ-resistant and 35 CQ-susceptible. A frequency of 7.1% of multi-copy pvcrt-o was observed in CQ-susceptible samples and 7.7% in CQ-resistant at D0 (P > 0.05) and 33.3% in CQ-resistant at DR (P < 0.05). For pvmdr1, 10.7% of the CQ-susceptible samples presented multiple copies compared to 11.1% in CQ-resistant at D0 and 0.0% in CQ-resistant at DR (P > 0.05). A deletion of 19 bp was found in 11/23 (47.6%) of the patients with CQ-susceptible P. vivax and 3/10 (23.1%) of the samples with in CQRPv at D0. At day DR, 55.5% of the samples with CQRPv had the 19 bp deletion. For the pvmdr-1 gene, was no variation in the analysed gene compared to the P. vivax reference Sal-1.

Conclusions

This was the first study with 42-day clinical follow-up to evaluate the variation of the number of copies and polymorphisms in the promoter region of the pvcrt-o and pvmdr1 genes in relation to treatment outcomes. Significantly higher frequency of multi-copy pvcrt-o was found in CQRPv samples at DR compared to CQ-susceptible, indicating parasite selection of this genotype after CQ treatment and its association with CQ-resistance in vivo.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2411-5) contains supplementary material, which is available to authorized users.

The prevalence of molecular markers of drug resistance in Plasmodium vivax from the border regions of Thailand in 2008 and 2014

The prevalence of Plasmodium vivax is increasing in the border regions of Thailand; one potential problem confounding the control of malaria in these regions is the emergence and spread of drug resistance. The aim of this study was to determine the genetic diversity in genes potentially linked to drug resistance in P. vivax parasites isolated from four different border regions of Thailand; Thai-Myanmar (Tak, Mae Hong Son and Prachuap Khiri Khan Provinces), and Thai-Cambodian borders (Chanthaburi Province). Isolates were collected from 345 P. vivax patients in 2008 and 2014, and parasite DNA extracted and subjected to nucleotide sequencing at five putative drug-resistance loci (Pvdhfr, Pvdhps, Pvmdr1, Pvcrt-o and Pvk12). The prevalence of mutations in Pvdhfr, Pvdhps and Pvmdr1 were markedly different between the Thai-Myanmar and Thai-Cambodian border areas and also varied between sampling times. All isolates carried the Pvdhfr (58R and 117N/T) mutation, however, whereas the quadruple mutant allele (I₅₇R₅₈M₆₁T₁₁₇) was the most prevalent (69.6%) in the Thai-Myanmar border region, the double mutant allele (F₅₇R₅₈T₆₁N₁₁₇) was at fixation on the Thai-Cambodian border (100%). The most prevalent genotypes of Pvdhps and Pvmdr1 were the double mutant (S₃₈₂G₃₈₃K₅₁₂G₅₅₃) (65.1%) and single mutant (M₉₅₈Y₉₇₆F₁₀₇₆) (46.5%) alleles, respectively on the Thai-Myanmar border while the single Pvdhps mutant (S₃₈₂G₃₈₃K₅₁₂A₅₅₃) (52.7%) and the triple Pvmdr1 mutant (M₉₅₈F₉₇₆L₁₀₇₆) (81%) alleles were dominant on the Thai-Cambodian border. No mutations were observed in the Pvcrt-o gene in either region. Novel mutations in the Pvk12 gene, the P. vivax orthologue of PfK13, linked to artemisinin resistance in Plasmodium falciparum, were observed with three nonsynonymous and three synonymous mutations in six isolates (3.3%).

Measuring ex vivo drug susceptibility in Plasmodium vivax isolates from Cambodia

Background

While intensive Plasmodium falciparum multidrug resistance surveillance continues in Cambodia, relatively little is known about Plasmodium vivax drug resistance in Cambodia or elsewhere. To investigate P. vivax anti-malarial susceptibility in Cambodia, 76 fresh P. vivax isolates collected from Oddar Meanchey (northern Cambodia) in 2013–2015 were assessed for ex vivo drug susceptibility using the microscopy-based schizont maturation test (SMT) and a Plasmodium pan-species lactate dehydrogenase (pLDH) ELISA. P. vivax multidrug resistance gene 1 (pvmdr1) mutations, and copy number were analysed in a subset of isolates.

Results

Ex vivo testing was interpretable in 80% of isolates using the pLDH-ELISA, but only 25% with the SMT. Plasmodium vivax drug susceptibility by pLDH-ELISA was directly compared with 58 P. falciparum isolates collected from the same locations in 2013–4, tested by histidine-rich protein-2 ELISA. Median pLDH-ELISA IC₅₀ of P. vivax isolates was significantly lower for dihydroartemisinin (3.4 vs 6.3 nM), artesunate (3.2 vs 5.7 nM), and chloroquine (22.1 vs 103.8 nM) than P. falciparum but higher for mefloquine (92 vs 66 nM). There were not significant differences for lumefantrine or doxycycline. Both P. vivax and P. falciparum had comparable median piperaquine IC₅₀ (106.5 vs 123.8 nM), but some P. falciparum isolates were able to grow in much higher concentrations above the normal standard range used, attaining up to 100-fold greater IC₅₀s than P. vivax. A high percentage of P. vivax isolates had pvmdr1 Y976F (78%) and F1076L (83%) mutations but none had pvmdr1 amplification.

Conclusion

The findings of high P. vivax IC₅₀ to mefloquine and piperaquine, but not chloroquine, suggest significant drug pressure from drugs used to treat multidrug resistant P. falciparum in Cambodia. Plasmodium vivax isolates are frequently exposed to mefloquine and piperaquine due to mixed infections and the long elimination half-life of these drugs. Difficulty distinguishing infection due to relapsing hypnozoites versus blood-stage recrudescence complicates clinical detection of P. vivax resistance, while well-validated molecular markers of chloroquine resistance remain elusive. The pLDH assay may be a useful adjunctive tool for monitoring for emerging drug resistance, though more thorough validation is needed. Given high grade clinical chloroquine resistance observed recently in neighbouring countries, low chloroquine IC₅₀ values seen here should not be interpreted as susceptibility in the absence of clinical data. Incorporating pLDH monitoring with therapeutic efficacy studies for individuals with P. vivax will help to further validate this field-expedient method.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-2034-2) contains supplementary material, which is available to authorized users.

Distribution of Mutations Associated with Antifolate and Chloroquine Resistance among Imported Plasmodium vivax in the State of Qatar

Plasmodium vivax is the most prevalent parasite worldwide, escalating by spread of drug resistance. Currently, in Qatar, chloroquine (CQ) plus primaquine are recommended for the treatment of P. vivax malaria. The present study examined the prevalence of mutations in dihydrofolate reductase (dhfr), dihydropteroate synthase (dhps) genes and CQ resistance transporter (crt-o) genes, associated with sulphadoxine-pyrimethamine (SP) and chloroquine resistance, among imported P. vivax cases in Qatar. Blood samples were collected from patients positive for P. vivax and seeking medical treatment at Hamad General Hospital, Doha, during 2013-2016. The Sanger sequencing method was performed to examine the single nucleotide polymorphisms in Pvdhfr, Pvdhps, and Pvcrt-o genes. Of 314 examined P. vivax isolates, 247 (78.7%), 294 (93.6%) and 261 (83.1%) were successfully amplified and sequenced for Pvdhfr, Pvdhps, and Pvcrt-o, respectively. Overall, 53.8% (N = 133) carried mutant alleles (58R/117N) in Pvdhfr, whereas 77.2% (N = 227) and 90% (N = 235) isolates possessed wild type allele in Pvdhps and Pvcrt-o genes, respectively. In addition, a total of eleven distinct haplotypes were detected in Pvdhfr/Pvdhps genes. Interestingly, K10 insertion in the Pvcrt-o gene was observed only in patients originating from the Indian subcontinent. The results suggested that CQ remains an acceptable treatment regimen but further clinical data are required to assess the effectiveness of CQ and SP in Qatar to support the current national treatment guidelines. In addition, limited distribution of genetic polymorphisms associated with CQ and SP resistance observed in imported P. vivax infections, necessitates regular monitoring of drug resistant P. vivax malaria in Qatar.

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.