Babesiosis is caused by intraerythrocytic protozoa of the genus Babesia. B. microti, the cause of most cases, is the etiologic agent in the northeastern and upper midwestern United States, and B. duncani is responsible for disease on the West Coast. B. divergens causes disease in Europe. The deer tick (Ixodes scapularis) transmits B. microti.
In the United States, infections occur most frequently in the Northeast and upper Midwest. In 2011, >1100 cases were reported in the United States, with ~75% of cases presenting in July and August; this number is probably an underestimate, given that most pts experience a mild and self-limiting disease and may not seek medical attention.
Most pts develop a mild illness, but immunosuppressed pts may have more severe disease.
- After an incubation period of 1-4 weeks, pts gradually develop fevers, fatigue, and weakness. Other symptoms may include chills, sweats, myalgias, arthralgias, headache, and—less often—photophobia, shortness of breath, and abdominal pain.
- Severe babesiosis is associated with parasitemia levels of >4%.
- - Risk factors include an age of >50 years, male gender, asplenia, HIV infection/AIDS, malignancy, hemoglobinopathy, and immunosuppression.
- - Complications include ARDS, DIC, CHF, renal failure, and splenic infarcts and rupture.
- - The fatality rate is 5-9% among all hospitalized pts and 20% among immunocompromised pts.
Giemsa-stained thin smears identify intraerythrocytic Babesia parasites, which appear round, pear-shaped, or ameboid.
- Ring forms resembling P. falciparum but without pigment are most common.
- Tetrads (“Maltese crosses”)—formed by four budding merozoites—are pathognomonic for B. microti and other small Babesia species.
- PCR and serology can also be used for diagnostic purposes.
Treatment: Babesiosis
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