Abstract
BackgroundKnowledge of the population genetics and transmission dynamics of Plasmodium vivax is crucial in predicting the emergence of drug resistance, relapse pattern and novel parasite phenotypes, all of which are relevant to the control of vivax infections. The aim of this study was to analyse changes in the genetic diversity of P. vivax genes from field isolates collected at different times along the Thai–Myanmar border.MethodsTwo hundred and fifty-four P. vivax isolates collected during two periods 10 years apart along the Thai–Myanmar border were analysed. The parasites were genotyped by nested-PCR and PCR–RFLP targeting selected polymorphic loci of Pvmsp1, Pvmsp3α and Pvcsp genes.ResultsThe total number of distinguishable allelic variants observed for Pvcsp, Pvmsp1, and Pvmsp3α was 17, 7 and 3, respectively. High genetic diversity was observed for Pvcsp (HE = 0.846) and Pvmsp1 (HE = 0.709). Of the 254 isolates, 4.3 and 14.6 % harboured mixed Pvmsp1 and Pvcsp genotypes with a mean multiplicity of infection (MOI) of 1.06 and 1.15, respectively. The overall frequency of multiple genotypes was 16.9 %. When the frequencies of allelic variants of each gene during the two distinct periods were analysed, significant differences were noted for Pvmsp1 (P = 0.018) and the Pvcsp (P = 0.033) allelic variants.ConclusionDespite the low malaria transmission levels in Thailand, P. vivax population exhibit a relatively high degree of genetic diversity along the Thai–Myanmar border of Thailand, in particular for Pvmsp1 and Pvcsp, with indication of geographic and temporal variation in frequencies for some variants. These results are of relevance to monitoring the emergence of drug resistance and to the elaboration of measures to control vivax malaria.
Highlights
Knowledge of the population genetics and transmission dynamics of Plasmodium vivax is crucial in predicting the emergence of drug resistance, relapse pattern and novel parasite phenotypes, all of which are relevant to the control of vivax infections
Most targeted polymorphic loci are found on single-copy P. vivax genes: msp1 coding for merozoite surface proteins (MSP1) (Pvmsp1), msp3alpha coding for another merozoite surface protein (Pvmsp3α), and csp coding for circumsporozoite protein (CSP)(Pvcsp)
This study aims to assess the genetic diversity using Pvmsp1F3, Pvmsp3α and circumsporozoite surface protein gene of Plasmodium vivax (Pvcsp) loci in P. vivax isolates collected along the Thai– Myanmar border, and to investigate whether variations in frequencies occur geographically and temporally
Summary
Knowledge of the population genetics and transmission dynamics of Plasmodium vivax is crucial in predicting the emergence of drug resistance, relapse pattern and novel parasite phenotypes, all of which are relevant to the control of vivax infections. The control of P. vivax poses particular problems because of this parasite’s propensity to relapse This is compounded by the emergence of drug resistance; recently, Many polymorphic genetic markers are available for characterizing P. vivax populations [4,5,6,7,8,9,10,11]. Pvmsp gene has a mosaic structure, with seven conserved blocks and six variable blocks [16]. Among these blocks, the variable block 10, previously designated as F3 fragment, is highly polymorphic and as such is a suitable genetic marker for population studies [5, 7, 17]. The three loci above are considered to be under selective immune pressure
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