Babesiosis, 2006

Babesiosis is a malaria-like illness caused by the protozoan Babesia microti. This parasite is transmitted to humans by bites from Ixodes scapularis (the deer tick or blacklegged tick), the same vector that transmits the agents of Lyme disease and Anaplasmosis (HA). B. microti can also be transmitted by blood transfusion.

In 2006, a record number of 18 babesiosis cases (0.4 cases per 100,000) were reported, nearly double the previous high of 10 cases in 2005. This is notably higher than the median number of cases reported annually from 1992 to 2004 (median, 3 cases; range, 1 to 7). Seven (39%) babesiosis case-patients reported in 2006 were male. The median age of case-patients was 60 years (range, 7 to 76 years). The peak in onsets of illness occurred in July and August (11 cases [61%]). In 2006, 69% of case-patients were hospitalized for their infection. One case-patient, whose infection likely occurred through blood transfusion, died from babesiosis in 2006.

Babesiosis co-infections with Lyme disease or HA can occur from the same tick bite, although the majority of babesiosis infections are asymptomatic. During 2006, three (17%) babesiosis case-patients also had objective evidence of Lyme disease, and two (11%) had objective evidence of HA. The risk for babesiosis is highest in many of the same Minnesota counties where the risk of Lyme disease and HA is greatest, especially in east-central and north-central Minnesota and western Wisconsin.

For a discussion of the recent increase in tick-borne disease in Minnesota and the distribution of ticks that transmit B. microti and other tick-borne diseases, see “Expansion of the Range of Vector-borne Disease in Minnesota” in the March/April 2006 issue (vol. 34, no. 2) of the DCN.

• For up to date information see>> For up to date information see:Babesiosis (Babesia microti)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2006