Volume 25-18
15 September 1999

[Table of Contents]

FIRST ISOLATION OF LYME DISEASE SPIROCHETE, BORRELIA BURGDORFERI, FROM BLACKLEGGED TICK, IXODES SCAPULARIS, REMOVED FROM A BIRD IN NOVA SCOTIA, CANADA

The Lyme disease spirochete, Borrelia burgdorferi, has been isolated from a blacklegged tick, Ixodes scapularis, removed from a songbird in Canada. On 28 May 1999, this engorged blacklegged tick nymph was removed from a common yellowthroat, Geothlypis trichas, collected during bird banding on Bon Portage Island, Nova Scotia.

The Atlantic Bird Observatory participated in collecting attached ticks from passerine birds banded on Seal Island and Bon Portage Island off the southwest tip of Nova Scotia. During spring migration, 21 ticks were collected from 12 individual birds (4 species) from 14 to 29 May 1999. These immature (larva, nymph) ticks on birds included the rabbit tick, Haemaphysalis leporispalustris, and I. scapularis (Table 1).

As part of a monitoring program of ticks on birds in southern Canada, these engorged ticks were forwarded for identification, and then sent by courier to the British Columbia Centre for Disease Control Society (BCCDCS) for spirochetal analysis. At the BCCDCS, the tick identifications were confirmed and the ticks were surface sterilized using 10% hydrogen peroxide followed by 70% isopropyl alcohol, and transferred to sterile tissue to remove excess water. Dead ticks underwent DNA analysis directly using polymerase chain reaction (PCR) testing. For live ticks, the midgut contents were cultured in Barbour-Stoenner-Kelly (BSK) II medium at 34° C, and cultures were checked weekly by dark-field microscopy. Within 10 days, characteristic motile spirochetes were observed in one culture.

The isolate was immunostained with monoclonal antibodies of B. burgdorferi, namely, OspA (31 kilodalton [kDa]), OspB (34 kDa), P39 (39 kDa), and flagellin (41 kDa), and found to be reactive. Using PCR, DNA amplification of the OspA gene was conducted on the isolate and confirmed positive for B. burgdorferi.

Table 1 Ticks retrieved from birds on Bon Portage Island and Seal Island, Nova Scotia, Canada, 14 to 29 May 1999

This is the first isolation of B. burgdorferi from a blacklegged tick removed from a migratory bird in Canada. In fact, it is the first isolation of B. burgdorferi in Nova Scotia. On route to Nova Scotia, tropical-wintering species of birds, (i.e. Swainson's thrush, northern waterthrush, and common yellowthroat) fly through the New England states which are endemic for Ixodes scapularis and Lyme disease. Interestingly, song sparrows, which overwinter in Nova Scotia, were only infested with rabbit ticks which are indigenous to the area⁽¹⁾. The first record of an I. scapularis (reported as I. dammini) removed from a bird in Canada was a nymph collected from a road-killed common yellowthroat at Windsor, Nova Scotia, in late May 1990⁽²⁾. Since then, researchers reported immature blacklegged ticks on an American robin and chipping sparrow at Thunder Cape on Sibley Peninsula, Ontario, in the late spring of 1995⁽³⁾. Of epidemiologic significance, the common yellowthroat acts as a competent reservoir for B. burgdorferi⁽⁴⁾ .Even though random occurrence of blacklegged ticks have been previously reported in Nova Scotia, no known population has been identified. The present evidence clearly points out that spring migratory birds are involved in bringing B. burgdorferi-infected I. scapularis ticks long distances into Canada.

References

1. Gregson JD. The Ixodoidea of Canada. Department of Agriculture of Canada, Science Service, Division of Entomology, 1956 (Publication 930):1-92.

2. Bell CR, Specht HB, Coombs BA. The search for Ixodes dammini and Borrelia burgdorferi in Nova Scotia. Can J Infect Dis 1992;3:224-30.

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

4. Anderson JF, Johnson RC, Magnarelli LA et al. Involvement of birds in the epidemiology of the Lyme disease agent Borreliaburgdorferi. Infect Immun 1986;51:394-96.

Source :

MG Morshed, PhD, RSM (CCM), Head, Vector-borne Diseases Laboratory, BCCDCS, Vancouver, B.C.; JD Scott, BSc (Agr.), President, Lyme Disease Association of Ontario, Fergus, Ont.; SN Banerjee, PhD, M. Banerjee, Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, B.C.; T Fitzgerald, BSc, Atlantic Bird Observatory, Department of Biology, Acadia University, Wolfville, N.S.; K Fernando, MSc, R Mann, RT, Vector-borne Diseases Laboratory, J Isaac-Renton, MD, PhD, FRCPC, Director, Provincial Laboratory, BCCDCS, Vancouver, B.C.

Editorial Comment

This report further extends observations of the blacklegged tick in areas of Canada not currently known to be endemic. To date, the blacklegged tick has been shown to be endemic at Long Point and Point Pelee on Lake Erie in southern Ontario. However, the blacklegged tick has been documented in Newfoundland, Nova Scotia, Prince Edward Island, New Brunswick, Quebec, mainland Ontario, Manitoba, and Saskatchewan; isolates of Borrelia burgdorferi have been made from ticks collected in several of these provinces (Prince Edward Island, New Brunswick, Quebec, mainland Ontario, Manitoba, and now Nova Scotia). Also, B. burgdorferi has been isolated from I. pacificus and I. angustus, from different locations in British Columbia. In Alberta, B. burgdorferi has been isolated from Haemaphysalis leporispalustris. These observations serve as an important reminder to the public in general, and physicians in particular, that Lyme disease can be contracted in Canada in areas not currently known to be endemic for this major tick vector.

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