Walsh & Hoyt: Clinical Manifestations

The clinical manifestations of babesiosis differ markedly between European and North American cases. Cases reported in Europe generally occur in splenectomized patients and present as a fulminant, febrile, hemolytic, and often fatal disease that initially may be mistaken for malaria. In contrast, most infections with Babesia species in the United States occur in otherwise healthy persons and produce either subclinical infection or a mild illness characterized by fever, hemolysis, and hemoglobinuria. Severe cases in the United States usually occur either in asplenic patients or in patients who are immunocompromised by age, drugs, or disease such as AIDS, but even severe cases are rarely fatal, as they are in Europe. In patients with Lyme disease and simultaneous babesiosis that is not fatal, the illness tends to be both more prolonged and more severe than with babesiosis alone. Most patients who develop babesiosis are adults, but children may also be infected.