[Studies on Plasmodium atheruri].

Plasmodium atheruri, a parasite of the African porcupine Atherurus africanus, is infective to splenectomised laboratory Rats and Mice, to Hamsters and to 2 exotic rodents which are easily bred in captivity: Calomys callosus and Meriones unguiculatus. Sporogony develops in Anopheles stephensi fed on Atherurus and on laboratory rodents; it is similar to that of the Rodent Plasmodia. Exoerythrocytic schizogony usually lasts 4 to 6 days but schizonts have been found in the liver of a porcupine at day 8. Schizogony in the blood (induced by inoculation of infected blood or by injections of sporozoites) follows two stages which are morphologically distinct: a) acute infections developing in clean Atherurus, following splenectomy of infected Atherurus or in laboratory rodents; it is characterized by large trophozoïtes, schizonts with 8 to 16 merozoites, gametocytes and infectivity to Anopheles. b) chronic infection which only occurs in the blood of Atherurus and follows the acute stage 15 to 21 days after its onset; it is characterized by small trophozoites and schizonts producing 4 merozoites. Thus it is thought that the chronic stage only occurs in the natural host when it is immunized. We think that, in nature, chronic schizogony maintains the parasitaemia through periods of low transmission and is followed by "recrudescences". The mechanisms that trigger the "recrudescences" are unknown but are probably connected with a decrease in the immune status of the host.