Immunization of Man against Falciparum and Vivax Malaria by Use of Attenuated Sporozoites

David F. ClydeUniversity of Maryland School of Medicine, Baltimore, Maryland 21201

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Vincent C. McCarthyUniversity of Maryland School of Medicine, Baltimore, Maryland 21201

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Roger M. MillerUniversity of Maryland School of Medicine, Baltimore, Maryland 21201

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William E. WoodwardUniversity of Maryland School of Medicine, Baltimore, Maryland 21201

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With strict adherence to ethical guidelines, a volunteer was immunized against sporozoites of Plasmodium falciparum and P. vivax, the antigen consisting of attenuated sporozoites of each species inoculated through bites of mosquitoes X-irradiated at a minimum dosage of 15,000 rads. On one occasion this dosage did not render all P. vivax sporozoites noninfective. Species specificity of antigen and antibody was demonstrated, but within each species a wide geographical diversity of strains proved interchangeably antigenic and susceptible to the antibody. Once immunized, the volunteer was protected for not more than 3 months and 6 months, respectively, from infective P. falciparum and P. vivax sporozoites, the duration of protection being reflected by a positive species-specific circumsporozoite reaction. Studies in this volunteer, and in two others immunized with P. falciparum sporozoites, did not reveal any increase in serum levels of immunoglobulins G and M.

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