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Information ⬇

[Section Outline]

Microbiology !!navigator!!

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, B. duncani is responsible for disease on the West Coast, and B. divergens-like organisms cause disease in Arkansas, Kentucky, Missouri, and Washington. The deer tick (Ixodes scapularis) transmits B. microti.

Epidemiology !!navigator!!

In the United States, infections occur most frequently in the Northeast and upper Midwest. In 2016, >1600 cases were reported in the United States, with ∼75% of cases presenting between June 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.

Clinical Manifestations !!navigator!!

Most pts develop a mild illness, but immunosuppressed pts may have more severe disease. Twenty percent of adults and 40% of children develop asymptomatic infection that may persist for >2 years.

  • 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. Lymphadenopathy is absent. Symptoms typically last 1-2 weeks, although fatigue may persist for months.
  • Severe babesiosis is associated with parasitemia levels of >4%.
    • Risk factors include an age of >50 years, neonatal prematurity, asplenia/hyposplenism, HIV infection/AIDS, malignancy, and immunosuppression.
    • Complications include ARDS, DIC, CHF, renal failure, hemophagocytic lymphohistiocytosis, and splenic infarcts and rupture.
    • The fatality rate is 3-9% among all hospitalized pts and 20% among immunocompromised pts and those who acquire the infection through blood transfusion.

Diagnosis !!navigator!!

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

  • Mild to moderate illness should be treated with atovaquone (750 mg PO q12h) plus azithromycin (500 mg PO on day 1 followed by 250 mg/d PO) for 7-10 days.
    • Clindamycin plus quinine is equally effective but not as well tolerated.
  • Severe disease should be treated with azithromycin (500 mg IV q24h) and atovaquone (750 mg PO q12h) for 7-10 days.
    • Clindamycin (300-600 mg q6h IV or 600 mg q8h PO) plus quinine (650 mg q6-8h PO) is an alternative.
    • Consider exchange transfusion in pts with high-level parasitemia (>10%); hemoglobin levels of ≤10 g/dL; or pulmonary, hepatic, or renal compromise.
    • Immunocompromised pts generally need longer courses of treatment (e.g., 6 weeks), with at least 2 weeks of therapy after parasites are no longer detected on blood smear.
  • B. duncani and B. divergens infections can be treated with IV clindamycin and quinine for 7-10 days.

Outline ⬆

Section 7. Infectious Diseases