The effect of pyrimethamine on the BI strain of Plasmodium gallinaceum.

Abstract

Summary Pyrimethamine, in large single doses administered on the seventh day of a sporozoite-induced BI strain Plasmodium gallinaceum infection, did not cure the infection though it did prevent death from exoerythrocytic parasites. After a period in which there were no microscopically detectable parasites and which varied slightly with the dose of drug, normal pigmented parasites were found. Erythrocytic parasites could be demonstrated by subinoculation of blood into susceptible recipients as early as 11 to 13 days after inoculation. Variable and reduced numbers of exoerythrocytic parasites were found rarely on direct examination as late as 36 days after inoculation, and more frequently by subinoculation of blood at least as late as the nineteenth day. Mosquitoes could be infected when parasitemia was on the increase. The resulting sporozoites produced only exoerythrocytic infections in untreated recipients, indicating no essential change in the characteristics of the strain. The response of the parasite to the drug remained unchanged during four such serial transfers, using treated chicks as donors.