Abstract
BackgroundPlasmodium vivax Duffy binding protein (PvDBP) plays an essential role in erythrocyte invasion and a potential asexual blood stage vaccine candidate antigen against P. vivax. The polymorphic nature of PvDBP, particularly amino terminal cysteine-rich region (PvDBPII), represents a major impediment to the successful design of a protective vaccine against vivax malaria. In this study, the genetic polymorphism and natural selection at PvDBPII among Myanmar P. vivax isolates were analysed.MethodsFifty-four P. vivax infected blood samples collected from patients in Myanmar were used. The region flanking PvDBPII was amplified by PCR, cloned into Escherichia coli, and sequenced. The polymorphic characters and natural selection of the region were analysed using the DnaSP and MEGA4 programs.ResultsThirty-two point mutations (28 non-synonymous and four synonymous mutations) were identified in PvDBPII among the Myanmar P. vivax isolates. Sequence analyses revealed that 12 different PvDBPII haplotypes were identified in Myanmar P. vivax isolates and that the region has evolved under positive natural selection. High selective pressure preferentially acted on regions identified as B- and T-cell epitopes of PvDBPII. Recombination may also be played a role in the resulting genetic diversity of PvDBPII.ConclusionsPvDBPII of Myanmar P. vivax isolates displays a high level of genetic polymorphism and is under selective pressure. Myanmar P. vivax isolates share distinct types of PvDBPII alleles that are different from those of other geographical areas. These results will be useful for understanding the nature of the P. vivax population in Myanmar and for development of PvDBPII-based vaccine.
Highlights
MethodsFifty-four P. vivax infected blood samples collected from patients in Myanmar were used
Plasmodium vivax Duffy binding protein (PvDBP) plays an essential role in erythrocyte invasion and a potential asexual blood stage vaccine candidate antigen against P. vivax
PvDBP is expressed on the merozoite of P. vivax and plays an essential role in erythrocyte invasion of the parasite by mediating irreversible binding with its corresponding receptor, the duffy antigen receptor for chemokines
Summary
Blood samples and DNA preparation The 54 blood samples used in this study were collected from patients who were infected with Plasmodium vivax at Wet-Won Station Hospital, Pyin Oo Lwin township, Mandalay Division, Myanmar between 2004 and 2006 [24]. The confirmation of P. vivax infection was performed by microscopic examination of thin and thick blood smears and polymerase chain reaction [24]. The number of segregating sites (S), haplotype diversity (Hd), nucleotide diversity (π), and average number of pairwise nucleotide differences within the population (K) were calculated using the DnaSP ver. Analysis of polymorphism associated with B- and T- cell epitopes To assess the possibility that diversity in PvDBPII within the Myanmar P. vivax isolates may have arisen from host’s immune pressure, the genetic diversity in predicted or known B- and T-cell epitopes [14] and MHC binding regions [30] in PvDBPII was examined. Recombination parameters and linkage disequilibrium The recombination parameter (R), which included the effective population size and probability of recombination between adjacent nucleotides per generation, and the minimum number of recombination events (Rm) were measured using DnaSP ver. Linkage disequilibrium (LD) between different polymorphic sites was computed in terms of the R2 index
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