The Vectors of Simian Malaria: Identity, Biology, and Geographical Distribution

Abstract

Prior to 1960, no natural vectors were known for any species of simian malaria. In the course of investigations in Southeast Asia during the last 3 years, natural vectors for five of these malarias have been found; four have been transmitted in the laboratory. Natural vectors for the African and New World species are still unknown. In a series of tables, in the appendix, the authors summarize the literature on the potential experimental vectors. The ecology of simian malaria in Malaya is reviewed with particular reference to members of the Anopheles leucosphyrus group of mosquitoes in which three natural vectors of simian malaria have been identified. Because they are also vectors of human malaria, it is with this group of mosquitoes that the greatest possibility of a liaison between human and simian malaria exists in Southeast Asia. Interest in the vectors of simian malaria has been stimulated by the transmission of the Malayan monkey parasite Plasmodium cynomolgi bastianellii from man to monkeys by the bite of infected mosquitoes. The original infections in man were acquired accidentally in three different laboratories in the United States from experimentally infected Anopheles freeborni mosquitoes (Eyles et al., 1960; Schmidt et al., 1961). Subsequently other strains of Plasmodium cynomolgi, which is closely related to the human parasite P. vivax, were transmitted to man (Coatney et al., 1961) and it has been shown that man-to-man transmission of the parasite can occur under laboratory conditions. It is also known that the Central American monkey parasite, P. brasilianum, is transmissible to man (Contacos et al., 1963). These findings have led to efforts to determine the vectors of simian malaria in nature and to see whether there are ecological barriers Received for publication 8 October 1963. * Presented at the XVI International Congress of Zoology, Washington, D. C., on 21 August 1963 and sponsored by the American Society of Parasitologists and the British Society of Parasitology. t Present address: Division of Entomology, Commonwealth Scientific and Industrial Organization, Brisbane, Australia. which would prevent the transmission of monkey malaria to man under natural conditions in the field. These investigations have been centered mainly in Southeast Asia, particularly in Malaya, but it is pertinent at this stage to review briefly what is known about the vectors of simian malaria the world over. VECTORS OF SIMIAN MALARIA IN AFRICA Four members of the genus Plasmodium have been isolated from subhuman primates in Africa (Table I). Three species come from the great apes, Plasmodium reichenowi; a falciparum parasite of gorillas and chimpanzees; Plasmodium schwetzi, a vivax parasite of gorillas and chimpanzees; and Plasmodium malariae, a quartan parasite, similar to the human quartan parasite, of chimpanzees. The natural vectors of simian malaria are unknown in Africa, and information on the development of parasites under experimental conditions is scanty. Bray (1957) reported gut infections with Plasmodium reichenowi in experimentally fed Anopheles gambiae but mosquitoes dissected for gland infections were all negative. A similar observation was made by Rodhain and Lassman (1940) when they noted that A. atroparvus fed on chimpanzees infected with P. schwetzi developed gut infections, but no