When to suspect and how to monitor babesiosis.

In the past decade, cases of babesiosis in humans have been reported with increasing frequency, especially in the northeastern United States. Babesia microti (in the United States) and bovine strains (in Europe) cause most infections in humans. Most cases are tick-borne, although cases of transfusion-associated and transplacental/perinatal transmission have also been reported. Factors associated with more severe disease include advanced age, previous splenectomy and immunodeficient states. Symptoms include high fever, chills, diaphoresis, weakness, anorexia and headache. Later in the course of the illness, the patient may develop jaundice. Congestive heart failure, renal failure and acute respiratory distress syndrome are the most common complications. Therapy using the combination of quinine sulfate and clindamycin was the most commonly used treatment; however, atovaquone suspension plus azithromycin was recently reported an equally effective and less toxic therapy. Exchange transfusion, together with antibabesial chemotherapy, may be necessary in critically ill patients.