No abstract

Summary Babesiosis is a worldwide tick-borne zoonosis caused by hemoprotozoan parasites of the genus Babesia. Babesia microti is the main etiologic agent of human babesiosis and is endemic in the northeastern and the upper Midwestern United States. The geographic expansion of babesiosis has followed that of Lyme disease, but has remained more restricted. The emergence of human babesiosis poses a serious health threat in highly endemic areas. Fever is the salient feature of babesiosis and often is accompanied by a series of non-specific symptoms, explaining why diagnosis may be delayed or missed. The diagnosis is confirmed by identification of babesia organisms on Giemsa stained blood smears, detection of babesia DNA by PCR, or a four-fold rise in anti-babesia antibody titers in acute and convalescent sera. The disease may be severe or fatal, particularly in patients who are otherwise healthy but older than 50 years of age, and in patients who are immunocompromised regardless of age. Most patients have complete recovery following a standard 7 to 10 day course of antimicrobial therapy.

Immunocompromised people who are infected by B. microti are at risk of persistent relapsing illness. Such patients generally require antibabesial treatment for >or=6 weeks to achieve cure, including 2 weeks after parasites are no longer detected on blood smear.