Effect of pyrimethamine upon sporogony and pre-erythrocytic schizogony of Laverania falciparum.

Studies have been conducted in Liberia on the effect of pyrimethamine on the sporogony and, for the first time, on the pre-erythrocytic schizogony of Laverania falciparum. From the results reported here it is concluded that it may reasonably be assumed that a mass monthly regimen of pyrimethamine in Liberia could afford protection to the individual and to the mosquito and thus to the population at large, provided that resistance to pyrimethamine does not intervene.Pyrimethamine in single doses of 25 mg or 50 mg administered to gametocyte carriers was able to render gametocytes of L. falciparum uninfective to A. gambiae for periods up to 28 days after administration.Mosquitos feeding upon a malaria-free pyrimethamine-treated subject before or after feeding upon a non-treated gametocyte carrier became infected and sporozoites appeared in the salivary glands.Pyrimethamine administered in 12.5-mg doses 13 days before, 6 days before and 2 days after sporozoite infection or administered in 25-mg doses 35 days and 7 days before sporozoite infection disallowed the development of the pre-erythrocytic schizonts of L. falciparum in the livers of two chimpanzees.