The population dynamics in mosquitoes and humans of two Plasmodium vivax polymorphs distinguished by different circumsporozoite protein repeat regions.

The population dynamics of two Plasmodium vivax polymorphs were studied over a two-year period in a village in a hyperendemic area of Papua New Guinea in both the mosquito and human populations. Strains of P. vivax were distinguished by different circumsporozoite (CS) protein repeats, the VK210 (classic) and the VK247 (variant) polymorphs. In 1986, 34% of P. vivax CS protein-positive mosquitoes were of the VK247 type. Although the proportion of P. vivax sporozoite antigen-positive mosquitoes compared with all sporozoite-positive mosquitoes did not change from 1986 to 1987, the proportion of P. vivax-positive mosquitoes of the VK247 polymorph decreased significantly from 34% to 11% (5 of 45) in 1987. In 1986, 61% (47 of 77) of humans tested had IgGs that recognized the VK247 CS repeat, while only 26% (22 of 84) had IgGs that recognized the VK210 CS repeat. The observed fluctuation in the proportion of the two P. vivax CS protein polymorphs recorded in the mosquito population from 1986 to 1987 is consistent with a hypothesis of selection by humoral immune pressure on the VK247 strain.