Seroprevalence of Babesia microti infection in Canadian blood donors

BACKGROUNDHuman babesiosis, caused by the intraerythrocytic protozoan parasite Babesia microti, is primarily transmitted by tick bites and is also transmitted by transfusion. Infections have been identified in US blood donors close to Canadian borders. We aimed to assess the risk of transfusion-transmitted babesiosis in Canada by examining infections in ticks and seroprevalence in blood donors. STUDY DESIGN AND METHODSPassive surveillance (receipt of ticks submitted by the public) was used to identify regions for tick drag sampling (active surveillance, 2009-2014). All ticks were tested for B. microti using an indirect immunofluorescent antibody assay (Imugen, Inc.). Between July and December 2013, blood donations from selected sites (southern Manitoba, Ontario, Quebec, New Brunswick, and Nova Scotia) near endemic US regions were tested for antibody to B. microti. Donors completed a questionnaire about risk travel and possible tick exposure. RESULTSOf approximately 12,000 ticks submitted, 14 were B. microti positive (10 in Manitoba, one in Ontario, one in Quebec, two in New Brunswick). From active tick surveillance, six of 361 ticks in Manitoba were positive (1.7%), three of 641 (0.5%) in Quebec, and none elsewhere. There were 26,260 donors at the selected sites of whom 13,993 (53%) were tested. None were positive for antibody to B. microti. In 2013, 47% of donors visited forested areas in Canada, and 41% traveled to the United States. CONCLUSIONThe data do not suggest that laboratory-based testing is warranted at this time. However, there are indicators that B. microti may be advancing into Canada and ongoing monitoring of tick populations and donor seroprevalence is indicated.