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Babesiosis
is infection with Babesia sp.
Infections can be asymptomatic or produce a malaria-like illness
with fever and hemolytic anemia. Disease is most severe in asplenic
patients, the elderly, and those with AIDS. Diagnosis is by identifying Babesia in a peripheral blood smear,
serology, or PCR. Treatment, when needed, is with azithromycin plus
atovaquone or with quinine plus clindamycin.
Etiology
and Pathophysiology
In the US, Babesia microti is the most common cause of babesiosis. Rodents are the principal natural reservoir, and deer ticks of the family Ixodidae are the usual vectors. Larval ticks become infected while feeding on an infected rodent, then transform into nymphs that transmit the parasite to another animal or to a human. Adult ticks ordinarily feed on deer but also may transmit the parasite to humans. Babesia enter RBCs, mature, and then divide asexually. Infected erythrocytes eventually rupture and release organisms that invade other RBCs.
Endemic areas in the US include the islands and the mainland bordering Nantucket Sound in Massachusetts, eastern Long Island and Shelter Island in New York, coastal Connecticut, and New Jersey as well as foci in Wisconsin, Georgia, and California. Other Babesia sp transmitted by different ticks infect humans in areas of Europe. Babesiosis can also be transmitted by blood transfusion.
Symptoms,
Signs, and Diagnosis
Asymptomatic infection may persist for months to years and remain subclinical throughout its course in otherwise healthy people, especially those < 40 yr. When symptomatic, the illness usually starts after a 1- to 2-wk incubation period with malaise, fatigue, chills, fever, headache, myalgia, and arthralgia that may last for weeks. Hepatosplenomegaly with jaundice, mild to moderately severe hemolytic anemia, mild neutropenia, and thrombocytopenia may occur.
Infection is sometimes fatal, particularly in the elderly, asplenic patients, and those with AIDS. In such patients, babesiosis may resemble falciparum malaria, with high fever, hemolytic anemia, hemoglobinuria, jaundice, and renal failure. Splenectomy may cause previously acquired asymptomatic parasitemia to become symptomatic.
Most patients do not remember a tick bite. Diagnosis is usually made by finding Babesia in blood smears. Tetrad forms, although not common, are helpful diagnostic clues. Serologic and PCR tests are available.
Treatment
and Prevention
Asymptomatic patients require no treatment, but therapy is indicated for cases with persistent high fever, rapidly increasing parasitemia, and falling Hct. The combination of atovaquone 750 mg po q 12 h and azithromycin 500 mg po on day 1 and 250 to 500 mg once/day thereafter for 7 to 10 days is as effective as traditional therapy with quinine plus clindamycin and has fewer adverse effects. Pediatric dosage is atovaquone 20 mg/kg bid and azithromycin 12 mg/kg once/day for 7 to 10 days. Alternatively, quinine 650 mg po tid for 7 days plus clindamycin 600 mg po tid or 1.2 g IV bid for 7 to 10 days can be used. Pediatric dosage is quinine 8 mg/kg po tid plus clindamycin 7 to 14 mg/kg po tid. Exchange transfusion has been lifesaving in hypotensive patients with high parasitemia.
Standard tick precautions (see Sidebar 1: Rickettsiae and Related Organisms: Tick Bite Prevention ) should be taken by all in endemic areas. Asplenic people should be particularly cautious.
Last full review/revision November 2005
Content last modified November 2005
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