Exploring genetic polymorphisms among Plasmodium vivax isolates from the Thai-Myanmar borders using circumsporozoite protein (pvcsp) and ookinete surface protein (pvs25) encoding genes.

ABSTRACT

Plasmodium vivax malaria cases remain high along the Thai-Myanmar and Thai-Cambodia borders. Plasmodium vivax circumsporozoite protein (pvcsp) and Plasmodium vivax ookinete surface protein (pvs25) genes are promising molecular markers of the genetic diversity of P. vivax. This study investigated the genetic diversity of pvcsp and pvs25 in P. vivax isolates collected from the Thai-Myanmar border. The DNA samples were amplified, and the genotypes were analyzed by PCR-RFLP and DNA sequencing. Pvcsp genotypes, VK210, VK247, and mixed types, were found in 203 (91.9%), 15 (6.8%), and 3 (1.3%) of the isolates, respectively. Twenty-four allelic variants were observed, of which a high prevalence of VK210E and VK247E were reported. Two pvcsp variants, VK210C and VK210M showed significantly higher parasite density (46,234 (1154-144,000) vs. 25,606 (1373-68,878), respectively). The genetic diversity of pvcsp along the Thai-Myanmar border during 2002-2015 showed dynamic changes with both positive and negative selection. The frequency and distribution of pvcsp pattern might be changed over time and might be other factors contributing to gene selection. Three amino acid substitutions of pvs25, i.e., E97Q, I130T, and Q131K, were investigated with frequencies of 10 (4.5%), 221 (100%), and 204 (92.3%) isolates, respectively. There was no association between parasite density and pvs25 polymorphisms. The frequency of pvs25 polymorphism was similar to that previously reported, with the absence of random mutation. In conclusion, the genetic variation of pvcsp was changed over times whereas the genetic diversity of pvs25 was limited; these variations would be helpful for further vaccine development against P. vivax malaria.