Studies on Malaria in Chimpanzees

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Abstract
Summary Anopheles gambiae was fed on human subjects and on chimpanzees harboring Plasmodium malariae on 38 occasions. In many cases the mosquitoes became infected and on 5 occasions sporozoites of P. malariae of human origin were transmitted successfully to chimpanzees. No correlation between observed gametocytemia and infection in the mosquito was found. All attempts to infect A. gambiae with P. malariae of chimpanzee origin failed, but A. gambiae could be infected by feeding on chimpanzees harboring P. malariae of human origin. Pre-erythrocytic schizonts of P. malariae, 8, 9, 10, 11, 12 and 12.5 days old are described from the liver of chimpanzees. They lie in parenchyma cells, enlarge the host cell nucleus, show a peripheral vacuolation and in general are distinct from similar forms of other species of malaria parasites. The pre-erythrocytic schizonts of P. malariae found in one chimpanzee were apparently abnormal, being much smaller than normal, and they displayed a distinct distribution in the liver, being found in “nests” and close to the outside surfaces of the liver. The appearance of the gametocytes of P. malariae and their infectivity to A. gambiae are discussed. It is concluded that, while the microgametocyte of P. malariae is distinctive, the macrogametocyte cannot be distinguished. No conclusions about the infectivity of these gametocytes were possible. The interrelationships between man, chimpanzee, A. gambiae and their malaria parasites are described and discussed in relation to a possible zoonosis involving P. malariae and in relation to the phylogeny of the human malaria parasites. It is concluded that while a P. malariae zoonosis is possible it does not constitute an important threat at present.

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