PLASMODIUM-VIVAX INFECTIONS IN CHIMPANZEES FOR SPOROZOITE CHALLENGE STUDIES IN MONKEYS

The development and testing of vaccines directed against Plasmodium vi vax has relied on Saimiri and Aotus monkeys as the animal test system and on chimpanzees to provide infective gametocytes to produce sporozo ites for monkey challenge studies and vaccine development. One sporozo ite-induced and 29 blood-induced infections with the Salvador I strain of P. vivax were studied in splenectomized chimpanzees. Eighteen prim ary infections with P. vivax resulted in maximum parasite counts rangi ng from 1,519 to 81,810/mu l (median 29,100/mu l). Twelve infections i nduced in animals previously infected with the homologous or heterolog ous strains of P. vivax had maximum parasite counts ranging from 155 t o 14,136/mu l (median 1,736/mu l). A total of 202 of 237 lots containi ng a total of 293,175 Anopheles freeborni, An. stephensi, An. gambiae, An. dirus, An. quadrimaculatus, and An. maculatus mosquitoes were inf ected by membrane feeding on gametocytes from chimpanzees. Despite low er levels of parasitemia during secondary (reinfection) parasitemia, 6 6 of 70 lots of mosquitoes (94.3%) were infected. Based on the mean nu mber of oocysts per positive mosquito gut, An. freeborni was more heav ily infected than An. stephensi; An. stephensi was more heavily infect ed than An. gambiae; there was no significant difference between An. s tephensi and An. dirus. Sporozoites from An. stephensi, An. gambiae, A n. dirus, and An. freeborni infected with the Salvador I strain of P. vivax produced in chimpanzees were used to infect 193 Saimiri and six Aotus monkeys as well as one chimpanzee.