The patient has babesiosis caused by Babesia microti, which is transmitted by a tick bite. Most cases occur in the coastal northeast United States. Patients usually present with fever and hemolysis and occasionally splenomegaly. The illness closely mimics malaria, but malaria is not endemic in the United States. Although Lyme disease is transmitted by the same vector, this patients presentation is not compatible with Lyme disease (eg, erythema migrans; in later stages, fever and malaise associated with meningitis and heart block). Bartonellosis is caused by cat exposure and is not usually associated with hemolysis. This patients splenomegaly, anemia due to hemolysis, and thrombocytopenia are not compatible with a viral illness.
Mandell GL, Bennett JE, Dolin R, editors. Mandell, Douglas, and Bennetts principles and practice of infectious diseases. 6th ed. New York: Elsevier/Churchill Livingstone; 2005.
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