Sporozoites of 3 isolates of Plasmodium cynomolgi dissected from the salivary glands of Anopheles dirus and Anopheles quadrimaculatus were injected intravenously into 9 New World monkeys. Liver stage parasites were demonstrated in all 9 animals; 7 of these animals also produced blood stages after prepatent periods of 9 to 23 days.

Studies were conducted to determine the susceptibility of Anopheles farauti to different species and strains of Plasmodium. Mosquitoes were infected by feeding on animals or cultures infected with different strains of P. vivax, P. falciparum, P. ovale, P. coatneyi, P. gonderi, P. simiovale, P. knowlesi, and P. brasilianum. Infections of P. vivax and P. coatneyi were transmitted via sporozoites from An. farauti to monkeys. Comparative infection studies indicated that An. farauti was less susceptible to infection than An. stephensi, An. gambiae, An. freeborni, and An. dirus with the Salvador I strain of P. vivax, but more susceptible than An. stephensi and An. gambiae to infection with the coindigenous Indonesian XIX strain.

Attempts were made to infect Aotus and Saimiri monkeys with sporozoites of 3 strains of Plasmodium knowlesi to determine the potential of these animals in a monkey/malaria model. Splenectomized Saimiri and Aotus monkeys were infected with the H strain of P. knowlesi via sporozoites from Anopheles dirus mosquitoes. Prepatent periods ranged from 5 to 16 days. Saimiri monkeys infected with the Philippine strain had prepatent periods ranging from 6 to 8 days. Saimiri monkeys infected with the Hackeri strain had prepatent periods ranging from 6 to 11 days. Exoerythrocytic (EE) stages of the Philippine strain were readily demonstrated; EE stages of the H strain were less abundant. Results indicate that the Philippine strain of P. knowlesi in Saimiri monkeys has a course of parasitemia and EE stages similar to those previously seen in macaques and could serve as a reproducible model for biologic and immunologic studies.