Distribution of Ixodes pacificus and Ixodes scapularis re concurrent babesiosis and Lyme disease.

In Canada, the western blacklegged tick, Ixodes pacificus and the blacklegged tick, Ixodes scapularis, are the principal vectors of Borrelia burgdorferi, the causative agent of Lyme borreliosis. These two tick species are also capable of transmitting Babesia microti, the pathogen which causes human babesiosis, although locally acquired cases have yet to be reported in Canada. At the present time, I. pacificus is endemic to localized areas of southern British Columbia in the vicinity of the Fraser Delta, and on the Gulf Islands and Vancouver Island. Similarly, reproducing populations of I. scapularis are currently only known to be established on the Long Point peninsula and Point Pelee National Park, both of which are located on Lake Erie, Ontario. Although specimens of I. scapularis have been collected at widely scattered localities in all provinces of Canada between Manitoba and Newfoundland, at most of these localities only individual or small numbers of adult ticks (usually females) have been encountered, usually on dogs or people. This suggests that these ticks have been adventitiously introduced to these widely scattered areas, likely on birds, but does not indicate that tick populations are established. Similar introductions of I. pacificus to non-endemic regions of British Columbia likely occur but have not been documented to date. Thus at the present time, established populations of I. pacificus and I. scapularis are focal and limited in Canada.