Late relapse of Plasmodium ovale malaria–Philadelphia, Pennsylvania, November 2004

Approximately 1,300 cases of malaria are reported each year in the United States; nearly all of these cases occur in travelers, many of whom fail to receive or adhere to prescribed chemoprophylaxis or do not follow recommendations for prevention of mosquito bites. Malaria can persist if not treated or if treated incorrectly (e.g., with an ineffective drug or an incorrect dosage of an effective drug). Early treatment is required to avoid severe illness or death. Although malaria typically becomes clinically apparent within 1 month of infection, cases can occur years after the last presumed exposure. In November 2004, CDC received a report of a late relapse of malaria in a Nigerian man aged 23 years in Philadelphia, Pennsylvania. His malaria was determined to have been caused by Plasmodium ovale, one of the four species of Plasmodium parasite that are transmitted by mosquitoes and cause malaria. The patient had been treated for malaria in Nigeria on multiple occasions, most recently 6 years before onset of his illness in the United States. This report describes the Philadelphia case, which underscores the importance of taking a detailed travel and immigration history when evaluating unexplained fever and considering malaria in the differential diagnosis.