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| Travelers to forested areas of Southeast Asia and South America have gotten malaria caused by a malaria parasite species—Plasmodium knowlesi—normally found only in monkeys. This species can cause severe illness and death in people, but under the microscope, the parasite looks similar to a more benign human malaria species. Physicians should take special care in diagnosis and treatment. |
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Long-tailed Macaque. Credit: Jupiter images |
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Treat P. knowlesi Malaria as an Emergency
Giemsa-stained thin blood smear with schizonts (block arrow) and ring forms (thin arrow) of P. knowlesi from the reported case. Credit: Div of Infectious Diseases, New York State Dept of Health
Under the microscope, mature forms of the simian malaria species Plasmodium knowlesi look very much like P. malariae. Consequently, P. knowlesi has sometimes been misdiagnosed as P. malariae. Because P. malariae usually causes a mild malaria infection syndrome, patients diagnosed with this parasite are typically given a prescription and then sent home. However, P. knowlesi can be fatal, and physicians should treat patients with P. knowlesi or P. malariae infection as they would patients with the most lethal strain of malaria, P. falciparum—as an emergency—and admit them to the hospital for treatment and observation.
Additional Species of Simian Malaria Can Also Confuse
Along with P. knowlesi, there are additional species of simian malaria found in parts of Asia and South America that might be causing human infections. These simian species resemble the four traditional human species of malaria and so would also be unrecognized by the standard diagnostic methods. Health-care providers and laboratories diagnosing a case of malaria from Asia or non-falciparum malaria from South America should refer specimens for species confirmation to a CLIA-approved State Health Reference Laboratory and/or the CDC Division of Parasitic Diseases Reference Laboratory for species confirmation by molecular testing.
Case Report
Simian Malaria in a US traveler — Suffolk County, New York, 2008, in CDC's March 2009 MMWR, includes a case report of a woman born in the Philippines but living in the United States for 25 years who returned to her home country to visit and contracted malaria caused by P. knowlesi. Note: She had not taken any drugs to prevent malaria and did not protect herself from mosquitoes.
Clinical Advice
Health-care providers with questions regarding diagnosis or treatment should call the CDC Malaria Hotline: 770-488-7788 (M-F, 8am-4:30pm, Eastern Standard Time). For emergency consultation after hours, call: 770-488-7100 and request to speak with a CDC Malaria Branch clinician.
Page last modified : March 12, 2009
Content source: Division of Parasitic Diseases
National Center for Zoonotic, Vector-Borne, and Enteric Diseases (ZVED)
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