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 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.