Studies in Human Malaria

Abstract

Summary and Conclusions A more than twenty-five-fold resistance to pyrimethamine was induced in the Chesson strain of Plasmodium vivax by treating blood-inoculated infections with gradually increasing dosages of the drug over prolonged periods. This acquired resistance was transferable by the mosquito. These pyrimethamine-resistant infections were also resistant to chlorguanide but remained as sensitive to chloroquine as the parent strain. Because the development of resistance was obtained only after careful planning and execution, it appears doubtful if resistance will become a serious problem under field conditions.