Repeated infection of Aotus monkeys with Plasmodium falciparum induces protection against subsequent challenge with homologous and heterologous strains of parasite

We evaluated repeated blood-stage infections with Plasmodium falciparum in eight Aotus lemurinus lemurinus monkeys. Over the course of seven infections with 10(4) P. falciparum (the Vietnam Oak Knell [FVO] strain), the pre-patent period lengthened from 8.2 to 30.8 days; the peak parasitemia decreased from 4.5 x 10(5) to 0 parasites/mul (Challenges 6 and 7), and the requirement for treatment decreased from 100% to 0% (Challenges 3 to 7). Five weeks after the seventh FVO challenge, the eight immune and three naive monkeys received 10(4) parasitized erythrocytes infected with P. falciparum (CAMP strain). The three control animals experienced uncontrolled parasitemias reaching between 4.8 and 7.7 x 10(5) parasites/mul (pre-patency = 6.3 days) and all required drug treatment; six of the eight immune monkeys became parasitemic (pre-patency = 8.8 days), but self-cured. Two of three of the monkeys having the greatest reductions in hematocrit (50-60%) also had the highest parasitemias (similar to 10(4) parasites/mul) before self-curing. Repeated homologous infections induced sterile immunity to homologous challenge; during heterologous challenge the monkeys developed clinically relevant, but not life-threatening, parasitemias and anemia.