Asymptomatic Natural Human Infections With the Simian Malaria Parasites Plasmodium cynomolgi and Plasmodium knowlesi

Background In Southeast Asia, Plasmodium knowlesi, a parasite of long-tailed macaques (Macaca fascicularis), is an important cause of human malaria. Plasmodium cynomolgi also commonly infects these monkeys, but only one naturally acquired symptomatic human case has been reported previously.