Experimental infection of the squirrel monkey (Saimiri sciureus) with Plasmodium falciparum

Seventy-six squirrel monkeys, Saimiri sciureus, caught in Guyana and French Guiana, were examined for their susceptibility to infection with a strain of Plasmodium falciparum. Twenty-nine serial transfers were performed, both in splenectomized and intact animals. After a period of "adaptation," the strain became more virulent for the squirrel monkey and high parasitemias were obtained in splenectomized animals. Frequently, such infections led to the death of infected animals. In intact squirrel monkeys, a consistent parasitemia was observed in most animals, but with a less regular pattern and a lower level of infection. Cultivation of infected erythrocytes from squirrel monkeys and human erythrocytes confirmed that the parasite had kept its infectivity for human cells after a long period of serial syringe-transfers in the squirrel monkey, and tht the virulence for the Saimiri remained unchanged after 1-mo, in vitro progagation in human erythrocytes. All erythrocytic forms of the schizogonic cycle were observed in the bloodstream, and there was a certain synchronicity of the cycle. Gametocytes were not detected in infected animals nor in in vitro cultures derived from a parasitized squirrel monkey. Our results indicate that all the squirrel monkey can be a useful host in the laboratory for studies on P. falciparum, and it may become more important as the supply of other species of monkeys diminishes.