Exploring Genetic Polymorphism of Plasmodium vivax Variant Interspersed Repeats (vir) 12, Subfamily E, in Clinical Samples From Thailand.

The Plasmodium vivax variant interspersed repeat (vir) gene family is the largest multigene family in human malaria parasites and belongs to the pir superfamily. These genes encode variant surface antigens that are thought to contribute to immune evasion and disease pathogenesis. Among them, vir 12 of subfamily E is relatively conserved but exhibits polymorphism that may provide useful insights into the genetic diversity of P. vivax. A total of 100 P. vivax DNA samples were collected from finger-prick blood specimens in Yala province, Thailand, between 2017 and 2019. The vir 12 gene was amplified and sequenced, and analyses were conducted to assess genetic diversity and neutrality tests. The vir 12 gene exhibited low genetic diversity (π = 0.00016) among studied isolates with 6 haplotypes. Neutrality tests indicated evidence of purifying selection, suggesting immune-driven evolutionary pressures. Comparative analysis with other geographic populations revealed both shared and region-specific alleles, highlighting localized transmission dynamics and underlying parasite population structure. This study demonstrates low genetic polymorphism of vir 12 in P. vivax populations from Yala province, Thailand, consistent with reports from other regions but with distinct patterns across endemic areas. These findings underscore the importance of investigating conserved members of the vir family to enhance our understanding of parasite adaptation and host-parasite interactions, with implications for malaria control and vaccine development.