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colon; Based on successful work with nonhuman malarias, an attempt was made to immunize man against mosquito-borne stages of Plasmodium falciparum. Strict ethical guidelines were followed. Mosquitoes carrying sporozoites of P. falciparum were X-irradiated and then fed on volunteers who had not previously been exposed to malaria. The sporozoites were inactivated at a minimum dosage of 15,000 rads, and did not produce adverse reactions in the volunteers. Three volunteers were each exposed during 84 days to 379 infected irradiated mosquitoes, and on day 98 were fed on by nonirradiated mosquitoes heavily infected with homologous strain P. falciparum. One of these men did not develop malaria, and continued to be immunized during the ensuing 217 days with 819 infected mosquitoes. On day 327, when antisporozoite antibody was first demonstrated in his serum by the circumsporozoite precipitation test, he was fed on by nonirradiated mosquitoes carrying homologous strain P. falciparum, and did not develop malaria. Possible causes of his failure to become infected were investigated, and it was concluded that he had become immunized to falciparum sporozoites of that strain. His continued susceptibility to strain-specific falciparum malaria induced by direct blood transfer was demonstrated.

(C) Copyright 1973 Southern Society for Clinical Investigation