Babesiosis, 2009

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

In 2009, a record number of 31 babesiosis cases (0.6 per 100,000 population) were reported, 2 cases more than the previous record of 29 cases in 2008. The median annual number of babesiosis cases since 2006 (median, 27 cases, range, 18 to 31) is notably higher than the median number of annual cases from 1996 to 2005 (median, 2 cases; range, 0 to 10). Nineteen (61%) babesiosis cases reported in 2009 were male. The median age of the cases was 61 years (range, 5 to 82 years). Onsets of illness were elevated from June through August and peaked in July (39% of cases). In 2009, 16 (52%) cases were hospitalized for their infection for a median duration of 5 days (range, 2 days to > 2 months). No cases died from complications of babesiosis in 2009.

Babesia co-infections with the etiologic agents of Lyme disease or anaplasmosis can occur from the same tick bite, although the majority of babesiosis infections are asymptomatic. During 2009, 3 (10%) babesiosis cases were also confirmed cases of Lyme disease, and 7 (23%) were confirmed or probable cases of anaplasmosis.

Two babesiosis cases during 2009 likely acquired B. microti from blood transfusions. The remainder reported probable I. scapularis exposures in counties of east-central, north-central, northwest, and southeastern Minnesota, and in Wisconsin, many of the same counties where the risk for Lyme disease and anaplasmosis is greatest.

• For up to date information see>> Babesiosis (Babesia microti)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2009