Immunization of owl monkeys to Plasmodium falciparum with merozoites from cultures of a knobless clone.

Summary Aotus trivirgatus monkeys of karyotype 2 were treated as follows. Three received two injections of purified merozoites of a knobless (K-) clone of Plasmodium falciparum with muramyl dipeptide as adjuvant; three received similar injections but with merozoites of a wild-type knobby (K+) strain; three controls received MDP with human erythrocytes in the amounts estimated to be present as contaminants in the merozoite preparations. A month after the second injection all nine monkeys were inoculated with parasites of the wild-type knobby strain from another infected Aotus. The monkeys that had received the K- material developed only extremely low infections markedly different from the infections in the controls. Of those that received K+ material, one died early with low parasitaemia, one was protected and one had the same level of infection as the controls. In the combined group of immunized animals, four out of six were protected.