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 infection s with 10(4) P. falciparum (the Vietnam Oak Knell [FVO] strain), the pre-pa tent period lengthened from 8.2 to 30.8 days; the peak parasitemia decrease d from 4.5 x 10(5) to 0 parasites/mul (Challenges 6 and 7), and the require ment for treatment decreased from 100% to 0% (Challenges 3 to 7). Five week s 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 re aching between 4.8 and 7.7 x 10(5) parasites/mul (pre-patency = 6.3 days) a nd all required drug treatment; six of the eight immune monkeys became para sitemic (pre-patency = 8.8 days), but self-cured. Two of three of the monke ys having the greatest reductions in hematocrit (50-60%) also had the highe st parasitemias (similar to 10(4) parasites/mul) before self-curing. Repeat ed homologous infections induced sterile immunity to homologous challenge; during heterologous challenge the monkeys developed clinically relevant, bu t not life-threatening, parasitemias and anemia.