Babesiosis is a rare, severe and sometimes fatal tick-borne disease caused by an infection with a red blood cell parasite.

Babesiosis is seen most frequently in the elderly or in immunocompromised individuals. Cases of this disease have been reported during spring, summer and fall in coastal areas in the northeastern United States, especially Nantucket Island off the Massachusetts shore and on Long Island, New York. Cases have also been reported in Wisconsin, California, Georgia and some European countries. Severe cases of babesiosis can occur in people who have had their spleen removed.

Babesiosis is caused by Babesia microti, a parasite transmitted by the bite of an infected deer tick. The tick is carried by meadow voles, mice and deer. Transmission to humans generally occurs from the bite of the nymph, while the adult tick generally feeds on deer. Transmission can also occur via contaminated blood transfusion.

The disease can cause fever, fatigue and hemolytic anemia lasting from several days to several months. Infections can occur without producing symptoms.

It may take from one to 12 months for symptoms to appear; less time for immuncompromised people.

It is not known whether past infection with babesiosis can make a person immune.

Standardized treatments for babesiosis have not been developed. However, some drugs used in the treatment of malaria have been found to be effective in a few patients with babesiosis.

It is important to control rodents around human habitation and to use tick repellents. It is helpful to wear light colored clothing (so you can see ticks and brush them off before they attach to your skin) and to tuck pants into socks when walking through tick-infested area.