CASE STUDY

Case # 5 Fever of unknown origin

Submitted by Grace Halleran, PA student

Diagnosis: Babesiosis

This patient spent a week in Montauk, the eastern end of Long Island where B. microti has been identified. An endemic foci of B. microti was established along the Eastern seaboard, particularly on Nantucket Island, Massachusetts, and Long Island, New York, and is emerging in rural New Jersey. This tick-borne disease is primarily found in the white-footed mouse, or meadow vole, and the cottontail rabbit, both of which inhabit Long Island. Two tick species, Dermacentor variabilis and Ixodes scapularis, feed on these hosts from May to September. Their life cycle has a period of maximum larval feeding during the late summer. The patient’s presence in Montauk in July provided 2 risk factors for babesiosis; geography and time. Because the mode of transmission of babesiosis is most commonly the tick-bite, (also transmitted by blood transfusion and through the placenta), it is surmised that the patient received a tick bite while on Long Island.

The first study of human babesiosis describes erythema chronicum migrans-like lesions in the early stages, similar to that of Lyme disease; however, in Lyme disease, which is caused by Borrelia burgdorferi, the rash is an expanding ring-like rash. Symptoms of babesiois typically begin 1-4 weeks after the bite; patients present with malaise, myalgia, anorexia, fatigue, and chills. Some patients will also have fevers, nausea, vomiting, and hemoglobinuria.

Laboratory results in a person infected with B. microti will show hemolytic anemia, thrombocytopenia, increased LDH, increased ESR, and increased hepatic enzymes. Many of the diseases listed in the differential diagnosis will cause these changes. In ehrlichiosis, the CSF is of more importance, with an increase in protein. In borrelia, the anemia is normocytic and there is an increase in white blood cells (WBC), not a decrease as seen in babesiosis. In Chagas’ disease there will be an increase in WBC and an increase in creatine kinase.

To make a definitive diagnosis of babesiosis, a peripheral smear was performed. This preferably should be a thin smear but a thick smear is done more routinely. When the peripheral smear was performed on this patient the laboratory used a Giemsa Stain and visualized rings of exoerythrocytic organisms, the absence of pigmented granules in infected RBCs, and a "maltese cross." The smear was followed by a polymerase chain reaction test with positive results.

Treatment of babesiosis depends on the severity of the disease. Most patients have a mild illness that resolves without treatment, and is targeted to those with high-level parasitemia (ranges 1% to 80%). The treatment regimen includes clindamycin, azithromycin, atovaquone, doxycycline, and quinine. The patient was started on a combination of piperacillin/tazobactam and doxycycline before the smear was completed and was advised to finish the course of antibiotics.

Visit the CDC Web site to learn more about babesiosis:
http://www.cdc.gov/ncidod/dpd/parasites/Babesia/default.htm