Abstract
Genetic diversity and population structure of Plasmodium vivax parasites are valuable to the prediction of the origin and spread of novel variants within and between populations, and to the program evaluation of malaria control measures. Using two polymorphic genetic markers, the merozoite surface protein genes PvMSP-3α and PvMSP-3β, we investigated the genetic diversity of four Southeast Asian P. vivax populations, representing both subtropical and temperate strains with dramatically divergent relapse patterns. PCR amplification of PvMSP-3α and PvMSP-3β genes detected three and four major size polymorphisms among the 235 infections examined, respectively, while restriction analysis detected 15 and 19 alleles, respectively. Samples from different geographical areas differed dramatically in their PvMSP-3α and PvMSP-3β allele composition and frequency. Samples tended to cluster on the basis of their PCR-RFLP polymorphism. These results indicated that different parasite genotypes were circulating in each endemic area, and that geographic isolation may exist. Multiple infections were detected in all four parasite populations, ranging from 20.5% to 31.8%, strongly indicating that P. vivax populations were highly diverse and multiple clonal infections are common in these malaria-hypoendemic regions of Southeast Asia.