With strict adherence to ethical guidelines, a semi-immune volunteer was exposed to homologous and heterologous blood challenges with strains of Plasmodium falciparum from Vietnam and Tanzania. On both occasions infections developed, but clinical manifestations were moderated, prepatent periods increased, and parasitemias limited. Gametocytes produced by these infections failed to infect Anopheles stephensi. Possible reasons for this are discussed.
Present address: Department of Tropical Medicine and Medical Parasitology, Louisiana State University Medical Center, 1542 Tulane Avenue, New Qrleans, Louisiana 70112.