Plasmodium vivax: Prevalence of mutations associated with sulfadoxine–pyrimethamine resistance in Plasmodium vivax clinical isolates from Pakistan

Phylogenetic analysis suggests single and multiple origins of dihydrofolate reductase mutations in Plasmodium vivax

Pyrimethamine was first introduced for the treatment of malaria in Asia and Africa during the early 1980s, replacing chloroquine, and has become the first line of drugs in many countries. In recent years, development of pyrimethamine resistance in Plasmodium vivax has become a barrier to effective malaria control strategies. Here, we describe the use of meta-barcoded deep amplicon sequencing technology to assess the evolutionary origin of pyrimethamine resistance by analysing the flanking region of dihydrofolate reductase (dhfr) locus. The genetic modelling suggests that 58R and 173L single mutants and 58R/117N double mutants are present on a single lineage; suggesting a single origin of these mutations. The triple mutants (57L/58R/117N, 58R/61M/117N and 58R/117N/173L) share the lineage of 58R/117N, suggesting a common origin. In contrast, the 117N mutant is present on two separate lineages suggesting that there are multiple origins of this mutation. We characterised the allele frequency of the P. vivax dhfr locus. Our results support the view that the single mutation of 117N and double mutations of 58R/117N arise commonly, whereas the single mutation of 173L and triple mutations of 57L/58R/117N, 58R/61M/117N and 58R/117N/173L are less common. Our work will help to inform mitigation strategies for pyrimethamine resistance in P. vivax.

Polymorphisms in Plasmodium vivax antifolate resistance markers in Afghanistan between 2007 and 2017

BACKGROUND

Plasmodium vivax is the predominant Plasmodium species in Afghanistan. National guidelines recommend the combination of chloroquine and primaquine (CQ-PQ) for radical treatment of P. vivax malaria. Artesunate in combination with the antifolates sulfadoxine-pyrimethamine (SP) has been first-line treatment for uncomplicated falciparum malaria until 2016. Although SP has been the recommended treatment for falciparum and not vivax malaria, exposure of the P. vivax parasite population to SP might still have been quite extensive because of community based management of malaria. The change in the P. vivax antifolate resistance markers between 2007 and 2017 were investigated.

METHODS

Dried blood spots were collected (n = 185) from confirmed P. vivax patients in five malaria-endemic areas of Afghanistan bordering Tajikistan, Turkmenistan and Pakistan, including Takhar, Faryab, Laghman, Nangarhar, and Kunar, in 2007, 2010 and 2017. Semi-nested PCR, RFLP and nucleotide sequencing were used to assess the pyrimethamine resistant related mutations in P. vivax dihydrofolate reductase (pvdhfr I13L, P33L, N50I, F57L, S58R, T61I, S93H, S117N, I173L) and the sulfonamide resistance related mutations in P. vivax dihydropteroate synthase (pvdhps A383G, A553G).

RESULTS

In the 185 samples genotyped for pvdhfr and pvdhps mutations, 11 distinct haplotypes were observed, which evolved over time. In 2007, wild type pvdhfr and pvdhps were the most frequent haplotype in all study sites (81%, 80/99). However, in 2017, the frequency of the wild-type was reduced to 36%, (21/58; p value ≤ 0.001), with an increase in frequency of the double mutant pvdhfr and pvdhps haplotype S58RS117N (21%, 12/58), and the single pvdhfr mutant haplotype S117N (14%, 8/58). Triple and quadruple mutations were not found. In addition, pvdhfr mutations at position N50I (7%, 13/185) and the novel mutation S93H (6%, 11/185) were observed. Based on in silico protein modelling and molecular docking, the pvdhfr N50I mutation is expected to affect only moderately pyrimethamine binding, whereas the S93H mutation does not.

CONCLUSIONS

In the course of ten years, there has been a strong increase in the frequency pyrimethamine resistance related mutations in pvdhfr in the P. vivax population in Afghanistan, although triple and quadruple mutations conferring high grade resistance were not observed. This suggests relatively low drug pressure from SP on the P. vivax parasite population in the study areas. The impact of two newly identified mutations in the pvdhfr gene on pyrimethamine resistance needs further investigation.

Selective sweep and phylogenetic models for the emergence and spread of pyrimethamine resistance mutations in Plasmodium vivax

Pyrimethamine resistance is a major concern for the control of human haemoprotozoa, especially Plasmodium species. Currently, there is little understanding of how pyrimethamine resistance developed in Plasmodium vivax in the natural field conditions. Here, we present for the first time evidence of positive selection pressure on a dihydrofolate reductase locus and its consequences on the emergence and the spread of pyrimethamine resistance in P. vivax in the Punjab province of Pakistan. First, we examined the dihydrofolate reductase locus in 38 P. vivax isolates to look for evidence of positive selection pressure in human patients. The S58R (AGA)/S117N (AAC) double mutation was most common, being detected in 10/38 isolates. Single mutation S117N (AAC), I173L (CTT) and S58R (AGA) SNPs were detected in 8/38, 2/38 and 1/38 isolates, respectively. The F57L/I (TTA/ATA) and T61M (ATG) SNPs were not detected in any isolates examined. Although both soft and hard selective sweeps have occurred with striking differences between isolates, there was a predominance of hard sweeps. A single resistance haplotype was present at high frequency in 9/14 isolates, providing a strong evidence for single emergence of resistance by the single mutation, characteristics of hard selective sweeps. In contrast, 5/14 isolates carried multiple resistance haplotypes at high frequencies, providing an evidence of the emergence of resistance by recurrent mutations, characteristics of soft selective sweeps. Our phylogenetic relationship analysis suggests that S58R (AGA)/S117N (AAC) and S117N (AAC) mutations arose multiple times from a single origin and spread to multiple different cities in the Punjab province through gene flow. Interestingly, the I173L (CTT) mutation was present on a single haplotype, suggesting that it arises rarely and has not spread between cities. Our work shows the need for responsible use of existing and new antimicrobial drugs and their combinations, control the movement of infected patients and mosquito vector control strategies.

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.

Naturally acquired immune responses to thrombospondin-related adhesion protein (TRAP) of Plasmodium vivax in patients from areas of unstable malaria transmission

A key tool for the control, elimination, and eradication of Plasmodium vivax is the development of an effective vaccine. The thrombospondin-related adhesion protein (TRAP) is one of the major sporozoite antigens that plays an important role in the invasion of mosquito salivary glands and hepatocytes by sporozoites. The main goal of this study was to evaluate the naturally acquired antibodies to the P. vivax TRAP (PvTRAP) in patients from malaria-endemic areas of Iran (n=116), Afghanistan (n=50), and Pakistan (n=50). The PvTRAP gene was expressed in Escherichia coli Rosetta (DE3)-pET23a and used as antigen in enzyme-linked immunosorbent assay (ELISA). The profile of immunoglobulin G (IgG) isotype and the avidity of IgG, IgG1, and IgG3 to PvTRAP, as well as the association between anti-PvTRAP isotype responses and host age were evaluated. Only 42.24% of Iranian, 38% of Afghani, and 44% of Pakistani patients infected with P. vivax had positive anti-PvTRAP IgG, and the prevalence of responders in the three countries did not differ significantly (P>0.05). Moreover, the prevalence of IgG1 and IgG3 antibody responses to PvTRAP showed no significant correlation with age (P>0.05). Individuals exposed to vivax malaria in the unstable malaria transmission areas are able to produce antibodies to the TRAP antigen at all ages in response to P. vivax infections. Finally, the presence of mature IgG1 and IgG3 antibodies with high to intermediate avidity against PvTRAP antigen (>60%) provide more information to understand the interactions between the host and P. vivax parasite. In summary, the present study provides data that support the rational development of an effective pre-erythrocytic stage vaccine based on PvTRAP antigen.

Low prevalence of dihydro folate reductase (dhfr) and dihydropteroate synthase (dhps) quadruple and quintuple mutant alleles associated with SP resistance in Plasmodium vivax isolates of West Bengal, India

Background

Emergence of chloroquine resistant Plasmodium vivax is a serious obstacle towards malaria control in India. This study elucidates the temporal pattern of antifolate [sulfadoxine–pyrimethamine (SP)] resistance in P. vivax infection by means of genetic polymorphisms, especially analysing the single nucleotide polymorphisms of dihydrofolate reductase (pvdhfr) and dihydropteroate synthase (pvdhps) gene among the field isolates of urban Kolkata Municipal Corporation and rural Purulia region of West Bengal, India.

Methods

Blood samples were collected from 99 microscopically diagnosed P. vivax patients (52 from Kolkata Municipal Corporation and 47 from Purulia). Parasitic DNA was extracted followed by polymerase chain reaction and sequencing of different codons of pvdhfr gene (15, 33, 50, 57, 58, 61, 64, 117, and 173 codons) and pvdhps gene (373, 380, 382, 383, 384, 512, 553, 585, and 601 codons) were performed to identify the mutations.

Results

Prevalence of double mutant dhfr A₁₅P₃₃N₅₀F₅₇R₅₈T₆₁V₆₄N₁₁₇I₁₇₃ allele (53.85 %) was observed in Kolkata Municipal Corporation (KMC) whereas in Purulia, wild dhfr A₁₅P₃₃N₅₀F₅₇S₅₈T₆₁V₆₄S₁₁₇I₁₇₃ allele was predominated (48.94 %). In pvdhps gene a significant number of isolates (17.31 %) in KMC contained the double mutant S₃₇₃E₃₈₀S₃₈₂G₃₈₃P₃₈₄K₅₁₂G₅₅₃V₅₈₅M₆₀₁ allele. pvdhfr and pvdhps combination haplotype revealed the emergence of quadruple (13.46 %) and quintuple (3.84 %) mutant allele in KMC, which might result in poor clinical response against antifolate drugs.

Conclusion

The study reveals that P. vivax parasites in rural Purulia may still be susceptible to SP but additional caution should be taken for treatment of vivax malaria in KMC to limit the blooming of quadruple and quintuple mutant allele in the remainder of the West Bengal, India.

Mutations of pvdhfr and pvdhps genes in vivax endemic-malaria areas in Kota Marudu and Kalabakan, Sabah

Background

Malaria cases persist in some remote areas in Sabah and Sarawak despite the ongoing and largely successful malaria control programme conducted by the Vector Borne Disease Control Programme, Ministry Of Health, Malaysia. Point mutations in the genes that encode the two enzymes involved in the folate biosynthesis pathway, dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) enzymes confer resistance to pyrimethamine and sulfadoxine respectively, in both Plasmodium falciparum and P. vivax. The aim of the current study was to determine the mutation on both pvdhfr at codon 13, 33, 57, 58, 61, 117, and 173 and pvdhps genes at codon 383 and 553, which are potentially associated with resistance to pyrimethamine and sulfadoxine in P. vivax samples in Sabah.

Methods

Every individual was screened for presence of malaria infection using a commercial rapid dipstick assay, ParaMax-3™ (Zephyr Biomedical, India). Individuals tested positive for P. vivax had blood collected and parasite DNA extracted. The pvdhfr and pvdhps genes were amplified by nested-PCR. Restriction fragment length polymorphism (RFLP) was carried out for detection of specific mutations in pvdhfr at codons 13Leu, 33Leu, 57Ile/Leu, 58Arg, 61Met, 117Asn/Thr, and 173Leu and pvdhps at codons 383Gly and 553Gly. The PCR–RFLP products were analysed using the Agilent 2100 Bioanalyzer (Agilent Technology, AS).

Results

A total of 619 and 2119 individuals from Kalabakan and Kota Marudu, respectively participated in the study. In Kalabakan and Kota Marudu, 9.37 and 2.45 % were tested positive for malaria and the positivity for P. vivax infection was 4.2 and 0.52 %, respectively. No mutation was observed at codon 13, 33 and 173 on pvdhfr and at codon 553 on pvdhps gene on samples from Kalabakan and Kota Marudu. One-hundred per cent mutations on pvdhfr were at 57Leu and 117Thr. Mutation at 58Arg and 61Met was observed to be higher in Kota Marudu 72.73 %. Mutation at 383Gly on pvdhps was highest in Kalabakan with 80.77 %. There are four distinct haplotypes of pvdhfr/pvdhps combination.

Conclusions

The presence of triple and quintuple mutation combination suggest that the P. vivax isolates exhibit a high degree of resistant to sulfadoxine, pyrimethamine and sulfadoxine-pyrimethamine combination therapy.

Genetic Polymorphisms in Plasmodium vivax Dihydrofolate Reductase and Dihydropteroate Synthase in Isolates from the Philippines, Bangladesh, and Nepal

Genetic polymorphisms of pvdhfr and pvdhps genes of Plasmodium vivax were investigated in 83 blood samples collected from patients in the Philippines, Bangladesh, and Nepal. The SNP-haplotypes of the pvdhfr gene at the amino acid positions 13, 33, 57, 58, 61, 117, and 173, and that of the pvdhps gene at the positions 383 and 553 were analyzed by nested PCR-RFLP. Results suggest diverse polymorphic patterns of pvdhfr alone as well as the combination patterns with pvdhps mutant alleles in P. vivax isolates collected from the 3 endemic countries in Asia. All samples carried mutant combination alleles of pvdhfr and pvdhps. The most prevalent combination alleles found in samples from the Philippines and Bangladesh were triple mutant pvdhfr combined with single mutant pvdhps allele and triple mutant pvdhfr combined with double wild-type pvdhps alleles, respectively. Those collected from Nepal were quadruple mutant pvdhfr combined with double wild-type pvdhps alleles. New alternative antifolate drugs which are effective against sulfadoxine-pyrimethamine (SP)-resistant P. vivax are required.

Molecular surveillance of pvdhfr, pvdhps, and pvmdr-1 mutations in Plasmodium vivax isolates from Yunnan and Anhui provinces of China

BACKGROUND

Plasmodium vivax is the predominant species of human malaria parasites present in China. Although sulphadoxine-pyrimethamine (SP) and chloroquine (CQ) have been widely used for malaria treatment in China, the resistance profiles of these drugs are not available. Analysis of dihydrofolate reductase (dhfr), dihydropteroate synthase (dhps), and multidrug resistance (mdr-1) gene mutations in P. vivax isolates is a valuable molecular approach for mapping resistance to SP and CQ. This study investigates the prevalence of pvdhfr, pvdhps, and pvmdr-1 of P. vivax clinical isolates from China and provides baseline molecular epidemiologic data on SP- and CQ-associated resistance in P. vivax.

METHODS

Plasmodium vivax clinical isolates were collected from two malaria-endemic regions of China, subtropical (Xishuangbanna, Yunnan province) and temperate (Bozhou, Anhui province), from 2009 to 2012. All isolates were analysed for single nucleotide polymorphism haplotypes in pvdhfr, pvdhps, and pvmdr-1 using direct DNA sequencing.

RESULTS

In pvdhfr, 15% of Xishuangbanna isolates carried wild-type (WT) allele, whereas the majority of isolates carried mutant genes with substitutions at five codons. Eight mutant haplotypes of pvdhfr were detected, while limited polymorphism of pvdhfr was found in Bozhou isolates. A size polymorphism was present in pvdhfr, with the three-repeat type being the most predominate in both Xishuangbanna (79%) and Bozhou (97%) isolates. In pvdhps, mutations at four codons were detected in Xishuangbanna isolates leading to six haplotypes, including WT allele, single-mutation, double-mutation, and triple-mutation alleles. All Bozhou isolates carried WT pvhdps. In pvmdr-1, isolates from Xishuangbanna carried mutations at codons Y976F and F1076L, whereas all isolates from Bozhou had only a single mutation at codon F1076L.

CONCLUSIONS

Plasmodium vivax isolates from subtropical and temperate zones of China are shown to have dramatically different frequencies and patterns of mutations in pvdhfr, pvdhps, and pvmdr-1. Whereas P. vivax populations in subtropical China are highly resistant to SP and CQ, those in the temperate zone may still be susceptible to SP and CQ. This information is useful for establishing treatment policy and provides a baseline for molecular surveillance of drug-resistant P. vivax in these areas.

Imported Plasmodium vivax malaria ex Pakistan

BACKGROUND

According to WHO, 1.5 million cases of malaria are reported annually in Pakistan. Malaria distribution in Pakistan is heterogeneous, and some areas, including Punjab, are considered at low risk for malaria. The aim of this study is to describe the trend of imported malaria cases from Pakistan reported to the international surveillance systems from 2005 to 2012.

METHODS

Clinics reporting malaria cases acquired after a stay in Pakistan between January 1, 2005, and December 31, 2012, were identified from the GeoSentinel (http://www.geosentinel.org) and EuroTravNet (http://www.Eurotravnet.eu) networks. Demographic and travel-related information was retrieved from the database and further information such as areas of destination within Pakistan was obtained directly from the reporting sites. Standard linear regression models were used to assess the statistical significance of the time trend.

RESULTS

From January 2005 to December 2012, a total of 63 cases of malaria acquired in Pakistan were retrieved in six countries over three continents. A statistically significant increasing trend in imported Plasmodium vivax malaria cases acquired in Pakistan, particularly for those exposed in Punjab, was observed over time (p = 0.006).

CONCLUSIONS

Our observation may herald a variation in malaria incidence in the Punjab province of Pakistan. This is in contrast with the previously described decreasing incidence of malaria in travelers to the Indian subcontinent, and with reports that describe Punjab as a low risk area for malaria. Nevertheless, this event is considered plausible by international organizations. This has potential implications for changes in chemoprophylaxis options and reinforces the need for increased surveillance, also considering the risk of introduction of autochthonous P. vivax malaria in areas where competent vectors are present, such as Europe.

Prevalence of mutations in the antifolates resistance-associated genes (dhfr and dhps) in Plasmodium vivax parasites from Eastern and Central Sudan

Plasmodium vivax is the most geographically widespread species, and its burden has been increasingly documented in Eastern and Central Sudan. P. vivax becomes the crucial challenge during elimination programs; thus an effective treatment is necessary to prevent the development and the spread of resistant parasites. Therefore, the main objective of the present study was to provide data on the prevalence of molecular markers in two genes (pvdhfr and pvdhps) associated with SP resistance after nine years of AS+SP deployment among P. vivax parasites from Eastern and Central Sudan using PCR-RFLP. During 2012-2013, a number of 66 blood spots were obtained on filter paper. The samples were collected before treatment from febrile patients who were microscopically positive for P. vivax, from three states in Eastern and Central Sudan (Gezira, Gedarif, and Kassala). Mutations were detected in three codons of pvdhfr (I13L, S58R, and S117N) and none in pvdhps. The majority of P. vivax parasites had double mutations (58R/117N, 58%) in dhfr gene, while all parasites were wild type in dhps gene. In addition, limited distinct haplotypes (n=4) were detected. In conclusion, the prevalence of mutations associated with SP resistance is low in Eastern and Central Sudan. Such information is necessary for guiding malaria control measures in the frame of Roll Back Malaria strategies for the elimination of malaria in the world.

Prevalence and patterns of antifolate and chloroquine drug resistance markers in Plasmodium vivax across Pakistan

Background

Plasmodium vivax is the most prevalent malaria species in Pakistan, with a distribution that coincides with Plasmodium falciparum in many parts of the country. Both species are likely exposed to drug pressure from a number of anti-malarials including chloroquine, sulphadoxine-pyrimethamine (SP), and artemisinin combination therapy, yet little is known regarding the effects of drug pressure on parasite genes associated with drug resistance. The aims of this study were to determine the prevalence of polymorphisms in the SP resistance-associated genes pvdhfr, pvdhps and chloroquine resistance-associated gene pvmdr1 in P. vivax isolates collected from across the country.

Methods

In 2011, 801 microscopically confirmed malaria-parasite positive filter paper blood samples were collected at 14 sites representing four provinces and the capital city of Islamabad. Species-specific polymerase chain reaction (PCR) was used to identify human Plasmodium species infection. PCR-positive P. vivax isolates were subjected to sequencing of pvdhfr, pvdhps and pvmdr1 and to real-time PCR analysis to assess pvmdr1 copy number variation.

Results

Of the 801 samples, 536 were determined to be P. vivax, 128 were P. falciparum, 43 were mixed vivax/falciparum infections and 94 were PCR-negative for Plasmodium infection. Of PCR-positive P. vivax samples, 372 were selected for sequence analysis. Seventy-six of the isolates (23%) were double mutant at positions S58R and S117N in pvdhfr. Additionally, two mutations at positions N50I and S93H were observed in 55 (15%) and 24 (7%) of samples, respectively. Three 18 base pair insertion-deletions (indels) were observed in pvdhfr, with two insertions at different nucleotide positions in 36 isolates and deletions in 10. Ninety-two percent of samples contained the pvdhps (S382/A383G/K512/A553/V585) SAKAV wild type haplotype. For pvmdr1, all isolates were wild type at position Y976F and 335 (98%) carried the mutation at codon F1076L. All isolates harboured single copies of the pvmdr1 gene.

Conclusions

The prevalence of mutations associated with SP resistance in P. vivax is low in Pakistan. The high prevalence of P. vivax mutant pvmdr1 codon F1076L indicates that efficacy of chloroquine plus primaquine could be in danger of being compromised, but further studies are required to assess the clinical relevance of this observation. These findings will serve as a baseline for further monitoring of drug-resistant P. vivax malaria in Pakistan.

Prevalence of drug resistance associated mutations in Plasmodium vivax against sulphadoxine-pyrimethamine in southern Pakistan

Background

In Pakistan, Plasmodium vivax and Plasmodium falciparum co-exist and usage of sulphadoxine-pyrimethamine (SP) against P. falciparum exposes P. vivax to the drug leading to generation of resistant alleles. The main aim of this study was to investigate frequency distribution of drug resistance associated mutations in pvdhfr, pvdhps genes and provide baseline molecular epidemiological data on SP-associated resistance in P. vivax from southern Pakistan.

Methods

From January 2008 to May 2009, a total of 150 samples were collected from patients tested slide-positive for P. vivax, at the Aga Khan University Hospital, Karachi, or its collection units located in Baluchistan and Sindh Province. Nested PCR using pvdhfr and pvdhps specific primers was performed for all samples.91.3% (137/150) of the samples were tested PCR positive of which 87.3% (131/137) were successfully sequenced. Sample sequencing data was analysed and compared against wild type reference sequences.

Results

In dhfr, mutations were observed at codons F57L, S58R and S117N/T. Novel non-synonymous mutations were observed at codon positions N50I, G114R and E119K while a synonymous mutation was observed at codon position 69Y. In dhps, mutations were observed at codon position A383G and A553G while novel non-synonymous mutations were observed at codon positions S373T, E380K, P384L, N389T, V392D, T393P, D459A, M601I, A651D and A661V.

Conclusion

This is the first report from southern Pakistan on SP resistance in clinical isolates of P. vivax. Results from this study confirm that diverse drug resistant alleles are circulating within this region.

Drug resistance associated genetic polymorphisms in Plasmodium falciparum and Plasmodium vivax collected in Honduras, Central America

Background

In Honduras, chloroquine and primaquine are recommended and still appear to be effective for treatment of Plasmodium falciparum and Plasmodium vivax malaria. The aim of this study was to determine the proportion of resistance associated genetic polymorphisms in P. falciparum and P. vivax collected in Honduras.

Methods

Blood samples were collected from patients seeking medical attention at the Hospital Escuela in Tegucigalpa from 2004 to 2006 as well as three regional hospitals, two health centres and one regional laboratory during 2009. Single nucleotide polymorphisms in P. falciparum chloroquine resistance transporter (pfcrt), multidrug resistance 1 (pfmdr1), dihydrofolate reductase (pfdhfr) and dihydropteroate synthase (pfdhps) genes and in P. vivax multidrug resistance 1 (pvmdr1) and dihydrofolate reductase (pvdhfr) genes were detected using PCR based methods.

Results

Thirty seven P. falciparum and 64 P. vivax samples were collected. All P. falciparum infections acquired in Honduras carried pfcrt, pfmdr1, pfdhps and pfdhfr alleles associated with chloroquine, amodiaquine and sulphadoxine-pyrimethamine sensitivity only. One patient with parasites acquired on a Pacific Island had pfcrt 76 T and pfmdr1 86Y alleles. That patient and a patient infected in West Africa had pfdhfr 51I, 59 R and 108 N alleles. Pvmdr1 976 F was found in 7/37 and two copies of pvmdr1 were found in 1/37 samples. Pvdhfr 57 L + 58 R was observed in 2/57 samples.

Conclusion

The results indicate that P. falciparum from Honduras remain sensitive to chloroquine and sulphadoxine-pyrimethamine. This suggests that chloroquine and sulphadoxine-pyrimethamine should be efficacious for treatment of uncomplicated P. falciparum malaria, supporting current national treatment guidelines. However, genetic polymorphisms associated with chloroquine and sulphadoxine-pyrimethamine tolerance were detected in local P. vivax and imported P. falciparum infections. Continuous monitoring of the prevalence of drug resistant/tolerant P. falciparum and P. vivax is therefore essential also in Honduras.

Molecular assessment of dhfr/dhps mutations among Plasmodium vivax clinical isolates after introduction of sulfadoxine/pyrimethamine in combination with artesunate in Iran

The increasing use of sulfadoxine/pyrimethamine (SP) for treatment of chloroquine-resistant Plasmodium falciparum has resulted in increased exposure of Plasmodium vivax parasites in areas where both species co-exist. In this study, the extent of mutations/haplotypes in pvdhfr and pvdhps was examined using PCR-RFLP methods in 427 P. vivax isolates in Iran after 4 years of introducing SP as the first-line anti-malarial drug in Iran. Mutations were detected in three codons of pvdhfr (F57L, S58R and S117N) and in one of pvdhps (A383G) and the majority of isolates had double mutations (58R/117N, 45.4%). In addition, the frequency of 57L mutation was detected in 8.2% of P. vivax isolates. This frequency was significantly increased when compared with a similar study on P. vivax isolates in 2005 (X(2) test, P<0.0001). Moreover, there was an increase in the frequency of single nucleotide polymorphisms at position 383G in pvdhps (0-2.6%) was found. Furthermore, the number of haplotypes increased from 6 to 12 in the study areas during 2006-2010. Interestingly, when combining the two loci, the frequency of parasites carrying pvdhfr/pvdhps pure mutations (L(57)R(58)/G(383), R(58)N(117)/G(383)) increased from 0% in 2006 to 2.1% in 2010. In conclusion, the present results suggest that SP could be effective in treatment against the erythrocytic stages of vivax malaria in Iran; however, the increased frequency of mutant haplotypes in Iran since 2006 is worrying and indicates the emergence of drug-tolerant/resistant P. vivax isolates in Iran in near future.