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Babesia infection can range from subclinical to severe. Symptoms, if any, usually develop within a few weeks or months after exposure but may first appear or recur many months later, particularly in persons who are or become immunosuppressed.

Clinically manifest Babesia infection is characterized by the presence of hemolytic anemia and nonspecific flu-like symptoms (e.g., fever, chills, body aches, weakness, fatigue). Some patients have splenomegaly, hepatomegaly, or jaundice.

Risk factors for severe babesiosis include asplenia, advanced age, and other causes of impaired immune function (e.g., HIV, malignancy, corticosteroid therapy). Some immunosuppressive therapies or conditions may affect the clinical manifestations (e.g., the patient might be afebrile). Severe cases can be associated with marked thrombocytopenia, disseminated intravascular coagulation, hemodynamic instability, acute respiratory distress, myocardial infarction, renal failure, hepatic compromise, altered mental status, and death.


Diagnosis of babesiosis requires a high index of suspicion, in part because the clinical manifestations are nonspecific. For acutely ill patients, the findings on routine laboratory testing frequently include hemolytic anemia and thrombocytopenia. Additional findings may include proteinuria, hemoglobinuria, and elevated levels of liver enzymes, blood urea nitrogen, and creatinine.

If the diagnosis of babesiosis is being considered, manual (non-automated) review of blood smears should be requested explicitly. In symptomatic patients with acute infection, Babesia parasites typically can be detected by light-microscopic examination of blood smears, although multiple smears may need to be examined. Sometimes it can be difficult to distinguish between Babesia and Plasmodium (especially P. falciparum) parasites and even between parasites and artifacts (such as stain or platelet debris). Consider having a reference laboratory confirm the diagnosis—by blood-smear examination and, if indicated, by other means, such as molecular and/or serologic methods tailored to the setting/species.

More on DPDx: Laboratory Diagnosis


Most asymptomatic persons do not require treatment. Treatment decisions should be individualized, especially for patients who have (or are at risk for) severe or relapsing infection.

For ill patients, babesiosis usually is treated for at least 7-10 days with a combination of two prescription medications — typically either:

  • Atovaquone PLUS azithromycin; OR
  • Clindamycin PLUS quinine (this combination is the standard of care for severely ill patients).

The typical daily doses for adults are provided in the table below.

Drug Adult dosage (usually treat for at least 710 days)
Atovaquone 750 mg orally twice a day
along with
Azithromycin On the first day, give a total dose in the range of 500–1000 mg orally; on subsequent days, give a total daily dose in the range of 250–1000 mg
Clindamycin 600 mg orally 3 times a day
300–600 mg intravenously 4 times a day
along with
Quinine 650 mg orally 3 times a day


Some patients—including those with severe illness—might require or benefit from supportive care, such as:

  • Antipyretics;
  • Vasopressors (if the blood pressure is low and unstable);
  • Blood transfusions;
  • Exchange transfusions (in which portions of a patient’s blood or blood cells are replaced with transfused blood components);
  • Mechanical ventilation; or
  • Dialysis