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Epidemiologic Notes and Reports Babesiosis -- Connecticut

Since August 1988, six cases of babesiosis--a rare protozoan parasitic disease-- have been reported to the Connecticut Department of Health Services (CDHS); only two cases thought to have been acquired in Connecticut were reported before 1988.

The first person became ill in August 1988; onset of illness in the other five persons occurred between late June and mid-August 1989. Ages ranged from 68 to 86 years; five were men. All six persons had fever, headache, and fatigue. Two of the patients were taking oral corticosteroids for chronic obstructive pulmonary disease; none were otherwise immunosuppressed, and none were asplenic. Four patients were treated with both quinine and clindamycin; one received quinine without clindamycin; the sixth received no specific therapy for babesiosis. All six are now asymptomatic, and their parasitemia has cleared.

Five of the patients (including the first case-patient) lived within 3 miles of each other; the sixth lived 22 miles away. None of the patients gave a history of recent travel to areas with known endemic babesiosis, and none had received blood transfusions before becoming ill. Gardening near the home was the principal outdoor activity of four persons; the other two walked in fields near their homes. Only one person recalled being bitten by a tick before becoming ill, and all six had observed mice in the areas around their homes.

For all six persons parasites were detected on peripheral blood smears. In addition, each had IgG antibody titers to Babesia microti of greater than or equal to 1:1024. B. microti was isolated (by hamster inoculation) from the blood of two patients and from eight (73%) of 11 mice trapped near four of the patients' homes. A statewide survey conducted in 1976-77 detected B. microti antibodies in mice collected in four of 22 sites (1). Three of these four sites are within 20 miles of five of the patients' homes and within 45 miles of the other patient's home.

The CDHS has alerted Connecticut physicians to the presence of a newly recognized focus of babesiosis within the state and has advised physicians to report all suspected cases. Surveys are planned to determine the extent of the infection in humans and rodents. Reported by: JJ Gadbaw, MD, Lawrence and Memorial Hospital, New London; JF Anderson, PhD, Connecticut Agricultural Experiment Station, New Haven; ML Cartter, MD, JL Hadler, MD, State Epidemiologist, Connecticut Dept of Health Svcs. Div of Parasitic Diseases, Center for Infectious Diseases; Div of Field Svcs, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: Babesia is a protozoan parasite of red blood cells. In the United States, babesiosis is most commonly caused by B. microti. Babesiosis was recognized in the Northeast in the 1960s and is endemic in Nantucket, Martha's Vineyard, Shelter Island, and parts of Long Island (2). In humans, B. microti infection may be subclinical or may present as a febrile illness with constitutional symptoms and anemia. Manifestations are most severe in elderly, immunosuppressed, or asplenic persons (3).

The natural hosts for B. microti include the white-footed mouse and the meadow vole. Tick bite by Ixodes dammini is the usual source of human infection. In addition, infection can be transmitted by blood transfusion (3). Entomologic surveys have detected increases in I. dammini and its spread to new areas (4). Physicians should be aware that babesiosis could occur in areas where Babesia was not previously considered endemic.


  1. Anderson JF, Magnarelli LA, Kurz J. Intraerythrocytic parasites in rodent populations of Connecticut: Babesia and Grahamella species. J Parasitol 1979;65:599-604.

  2. Golightly LM, Hirschhorn LR, Weller PF. Fever and headache in a splenectomized woman. Rev Infect Dis 1989;11:629-37.

  3. Ruebush TK III. Babesia. In: Mandell GL, Douglas RG Jr, Bennett JE, eds. Principles and practice of infectious diseases. 2nd ed. New York: Wiley, 1985:1559-60.

  4. Spielman A, Wilson ML, Levine JF, Piesman J. Ecology of Ixodes dammini-borne human babesiosis and Lyme disease. Annu Rev Entomol 1985;30:439-60.

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