Molecular epidemiology and genetic diversity of disappearing Plasmodium vivax in southern Thailand.

The evolution of genetic diversity and population structure of Plasmodium vivax as malaria elimination approaches remains unclear. This study analyzed the genetic variation and molecular epidemiology of P. vivax from Yala Province in southern Thailand, an area in the pre-elimination phase. Seventy P. vivax isolates, collected between 2017 and 2020, were genotyped for domain II of pvdbp and the 42-kDa region of pvmsp1 using amplicon deep sequencing. Data from Yala province were compared to published data from Tak province, where transmission was higher. Key analyses included nucleotide diversity (π), haplotype diversity (Hd), natural selection, recombination rates, and complexity of infection (COI). Genetic diversity in Yala was relatively low (π = 0.008 and 0.014; Hd = 0.774 and 0.407) compared to Tak (π = 0.012 and 0.027; Hd = 0.849 and 0.962). In Yala, polyclonal infections were found in 53.7% of pvdbp and 47.8% of pvmsp1 isolates, with average COI of 1.6 and 1.7. Both genes were under balancing selection. Distinct genetic differences were found between Yala and Tak in pvmsp1, providing a local genotypic profile useful for tracing parasite origins.