Babesiosis

Definition

Babesiosis is an infection of red blood cells caused by the single-celled parasite, Babesia microti, which is spread to humans by a tick bite.

Description

Babesiosis is a rare, tick-transmitted disease that is caused most often by the single-celled parasite Babesia microti. By 1995, fewer than 500 cases of babesiosis had been reported in the United States. The disease occurs primarily in New England and New York, especially on the coastal islands. However, cases have occurred in other parts of the United States. Because of tick activity, the risk for babesiosis is highest during June and July.

Ticks are small, blood-sucking arachnids. Although some ticks carry disease- causing organisms, most do not. Babesia microti is spread to humans through the bite of the tick Ixodes scapularis (also called Ixodes dammini). Ixodes scapularis, called the "blacklegged deer tick," usually feeds on deer and mice. A tick picks up the parasites by feeding on an infected mouse and then passes them on by biting a new host, possibly a human. To pass on the parasites, the tick must be attached to the skin for 36-48 hours. Once in the bloodstream, Babesia microti enters a red blood cell, reproduces by division, and destroys the cell. Humans infected with Babesia microti produce antibodies that can be helpful in diagnosing the infection.

Causes & symptoms

Persons who are over 40 years old, have had their spleen removed (splenectomized), and/or have a serious disease (cancer, AIDS, etc.) are at a greater risk for severe babesiosis. In severe cases of babesiosis, up to 85% of the blood cells can be infected. This causes a serious, possibly fatal, blood deficiency.

Diagnosis

Babesiosis can be diagnosed by examining a blood sample microscopically and detecting the presence of Babesia microti within the blood cells. The blood can also be checked for the presence of antibodies to the parasite.

Treatment

In serious cases, babesiosis is treated with a combination of clindamycin (Cleocin) and quinine. Clindamycin is given by injection and quinine is given orally three to four times a day for four to seven days. To reduce the number of parasites in the blood, severely ill patients have been treated with blood transfusions.

Prognosis

Otherwise healthy patients will recover completely. Babesiosis may last several months without treatment and is a severe, potentially fatal disease in splenectomized patients.

Prevention

The only prevention for babesiosis is to minimize exposure to ticks by staying on the trail when walking through the woods, avoiding tall grasses, wearing long sleeves and tucking pant legs into socks, wearing insect repellent, and checking for ticks after an outing. Remove a tick as soon as possible by grasping the tick with tweezers and gently pulling. Splenectomized people should avoid northeastern coastal regions during the tick season.

Key Terms

Anemia

A below normal number of red blood cells in the bloodstream.

Parasite

An organism which lives upon or within another organism.

Further Reading

For Your Information

Books

• Blood: Textbook of Hematology, 2nd ed., edited by James H. Jandl. Boston: Little, Brown and Company, 1996.
• Chiodini, Peter L. "Babesiosis." In Manson's Tropical Diseases, 20th ed. Philadelphia: W.B. Saunders, 1996.
• Infections and Diseases, 2nd ed., edited by Sherood L. Gorbach, John G. Bartlett and Neil R. Blacklow. Philadelphia: W.B. Saunders Company, 1997.

  Other

• Mayo Health Oasis 1998. http://www.mayohealth.org (5 March 1998).

Gale Encyclopedia of Medicine. Gale Research, 1999.