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By Richard D. Pearson, MD, Emeritus Professor of Medicine, University of Virginia School of Medicine

Babesiosis is infection of red blood cells caused by the single-celled protozoan parasite Babesia. The infection may cause fever, headache, body aches, and fatigue.

Babesia are protozoans that live inside red blood cells and eventually destroy them. Babesiosis is transmitted by the same type of deer ticks (family Ixodidae) that transmitsLyme disease.

This infection is common among animals but is relatively uncommon among people. In the United States, Babesia microti infects people on the offshore islands or coastal regions of Massachusetts, Rhode Island, Connecticut, eastern Long Island and Shelter Island in New York, and New Jersey. Cases also occur in Wisconsin and Minnesota. Other Babesia species infect people in the lower mid-West, Washington, and California and in other areas of the world.

Symptoms of Babesiosis

Some people, especially healthy people younger than 40, do not have noticeable symptoms. Other people have fever, headache, muscle and joint aches, and fatigue. The skin and the whites of the eyes may turn yellow (jaundice). Anemia may result from the breakdown of red blood cells. The liver and spleen often enlarge.

The risk of severe disease and death is highest for people whose spleen has been removed or who take drugs or have disorders that weaken the immune system (particularly AIDS). In these people, babesiosis symptoms may resemble those of malaria (causing a high fever, anemia, dark urine, jaundice, and kidney failure).

Diagnosis of Babesiosis

  • Examination of a sample of blood

To diagnose babesiosis, a doctor usually examines a blood sample under a microscope.

Treatment of Babesiosis

  • When treatment is needed, atovaquone plus azithromycin

Usually, no treatment is needed for a mild infection in healthy people with a functioning spleen because the infection typically disappears on its own. People with symptoms are usually treated with atovaquone plus azithromycin. Quinine plus clindamycin are also effective, but atovaquone and azithromycin have fewer side effects.

In areas where deer ticks are common, people can reduce the risk of getting the infection by taking precautions against ticks.