Volume 24-15
August 1, 1998

[Table of Contents]

Distribution of Ixodes pacificus and Ixodes scapularis re Concurrent Babesiosis and Lyme Disease(1)

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⁽²⁾. 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⁽³⁾.

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⁽³⁾. This suggests that these ticks have been adventitiously introduced to these widely scattered areas, likely on birds⁽⁴⁾, 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. Although people or pets living outside of the tick-endemic areas of British Columbia and Ontario can be infested locally by an adventitious tick, and hence potentially infected with any of the pathogens associated with these species, the probability of this occurring is low. This is reflected in the low number of indigenous cases of Lyme borreliosis reported in Canada. Similarly, because I. pacificus and I. scapularis are not widely established in Canada, the probability that humans who are infected with B. microti elsewhere will serve as reservoirs of infection for local populations of these ticks is equally small. However, this does not negate the importance of clinicians in Canada being aware of the possibility that these tick-transmitted diseases can occur.

References

1. dos Santos C, Kain K. Concurrent babesiosis and Lyme disease diagnosed in Ontario. CCDR 1998;24:97-101.

2. Gregson JD. The Ixodoidea of Canada. Ottawa, Ont.: Canadian Department of Agriculture, Division of Entomology, 1956 (Publication 930):1-92.

3. Lindsay LR, Barker IK, Surgeoner GA et al. Survival and development of Ixodes scapularis (Acari: Ixodidae) under various climatic conditions in Ontario, Canada. J Med Entomol 1995;32:143-52.

4. Klich M, Lankester M W, Wan Wu K. Spring migratory birds (Aves) extend the northern occurrence of blacklegged tick (Acari: Ixodidae). J Med Entomol 1996;33:581-85.

Source:

R Lindsay, PhD, H Artsob, PhD, Zoonotic Diseases Section, Bureau of Microbiology, Laboratory Centre for Disease Control, Winnipeg, MB; I Barker, PhD, DVM, Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON.

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