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

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Map of Southeast Asia. Credit: CIA Factbook

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 -- 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.

• Instruction and Specimen Submission Forms for Laboratories

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.

• Read the MMWR article: Simian Malaria in a US Traveler -- New York, 2008
• Read the NCZVED blog, Public Health Matters