Simian Malaria in a U.S. Traveler—New York, 2008

Four species of intraerythrocytic protozoa of the genus Plasmodium are known to cause malaria in humans. However, recent reports from Asia suggest the possibility that a fifth malaria species, Plasmodium knowlesi, is emerging as an important zoonotic human pathogen. Although more than 20 species of Plasmodium can infect non-human primates, until recently, naturally acquired human infections of simian malaria were viewed as rare events lacking public health significance. When viewed by light microscopy, many of the simian species are almost indistinguishable from the four Plasmodium species that cause infection in humans. Molecular techniques, such as polymerase chain reaction amplification and microsatellite analysis, are needed for definitive species determination. Here, the first recognized case of imported simian malaria in the US is described. A CDC editorial note is included.