THE EPIDEMIOLOGY OF PLASMODIUM-VIVAX CIRCUMSPOROZOITE PROTEIN POLYMORPHS IN THAILAND

Enzyme-linked immunosorbent assays (ELISAs) highly specific for the ch aracteristic repeat units of the circumsporozoite proteins of the VK 2 47 and VK 210 polymorphs of Plasmodium vivax were used to test sporozo ites produced by feeding mosquitoes on 1,711 human volunteers presenti ng at four locations in Thailand over five years. There was no evidenc e for the existence of any polymorph other than the two already descri bed. Based on the ELISAs, the overall prevalence of the VK 247 type wa s 29.5%, including those found mixed with VK 210. Relative proportions of VK 210 and VK 247 differed between collection sites. At all places , the ratio of VK 210 to VK 247 was significantly higher at the end of the nontransmission season than it was later during the annual monsoo n, suggesting that there may be intrinsic biological differences betwe en the polymorphs that affect their survival.