Gamete vaccines and transmission-blocking immunity in malaria.

We have recently proposed an approach to malaria control based on immunization of the host against extracellular malarial gametes, the stage in the mosquito guts, in order to block transmission by the mosquito vector. Our studies with avian and primate models have demonstrated that immunization of the host with extracellular gametes totally suppresses infectivity to the mosquito of a subsequent blood meal. Gametocytes within the erythrocytes are unaffected by the immunity, since resuspending the gametocytes in serum from normal nonimmune animals restores their infectivity to mosquitos. Immunity is mediated by antibodies that are ingested with the blood meal. These antibodies interact with extracellular gametes and prevent fertilization (the fusion of male and female gametes). Thus the infection in the mosquito is blocked, and in this way transmission is interrupted.