Clinical Features:
Most infections are probably asymptomatic, as indicated by serologic surveys.  Manifestations of disease include fever, chills, sweating, myalgias, fatigue, hepatosplenomegaly, and hemolytic anemia.  Symptoms typically occur after an incubation period of 1 to 4 weeks, and can last several weeks.  The disease is more severe in patients who are immunosuppressed, splenectomized, and/or elderly.  Infections caused by B. divergens tend to be more severe (frequently fatal if not appropriately treated) than those due to B. microti, where clinical recovery usually occurs.

Laboratory Diagnosis:
Diagnosis can be made by microscopic examination of thick and thin blood smears stained with Giemsa.  Repeated smears may be needed.

Diagnostic findings

• Microscopy
• Antibody detection by indirect fluorescent antibody (IFA) test is a complementary diagnostic test.
• Molecular methods

Isolation of the organisms by inoculation of patient blood into hamsters or gerbils may also assist in diagnosis.  Animals inoculated with infective blood typically develop parasitemia within 1 to 4 weeks.

Treatment:
Treatment with clindamycin* plus quinine or atovaquone* plus azithromycin* are the options.  The Medical Letter notes that exchange transfusion has been used in severely ill patients with high parasitemias.  For additional information, see the recommendations in The Medical Letter (Drugs for Parasitic Infections).

* These drugs are approved by the FDA, but considered investigational for this purpose.