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Volume 22-16 |
ISOLATION OF BORRELIA BURGDORFERI --- THUNDER BAY DISTRICT, ONTARIOThe Lyme disease (LD) spirochete, Borrelia burgdorferi, has been isolated from a black-legged tick, Ixodes scapularis (northern populations formerly considered I. dammini). This is the first time that a live culture of B. burgdorferi has been isolated in the Thunder Bay District. The tick was removed from the rump of a dog in Thunder Bay, Ontario on 31 October 1995. The dog had never travelled outside the city. During the 2 to 3-week period prior to the removal of the tick, the dog had a cough. The live tick was forwarded to the Vector-borne Diseases Laboratory, British Columbia Centre for Disease Control (BCCDC), Vancouver, British Columbia for spirochetal analysis. It was positively identified as I. scapularis. Prior to dissection, the fully engorged female tick was surfacesterilized in the laboratory using 10% hydrogen peroxide, followed by 70% isopropyl alcohol. The midgut contents were surgically removed, placed in BSK II culture medium, and incubated at 35° C. Cultures were checked weekly using dark-field microscopy. Within 2 weeks, characteristic motile spirochetes of B. burgdorferi were seen. Polymerase chain reacting (PCR) identified the genes of OspA, 16S rRNA, and HSP60 of B. burgdorferi in the isolate. The OspA [31 kilodaltons (kDa)], OspB (34 kDa), OspC (22-25 kDa), P39 (39 kDa), flagellin (41 kDa), HSP60 (60 kDa), and 66 kDa bands were profiled using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isolate was further analyzed for plasmid profile; pulsed-field gel electrophoresis (PFGE) separation of macrorestriction digests (MluI and SmaI) of total DNA was also carried out. A 135 kbp PFGE band, characteristic of B. burgdorferi sensu stricto, was detected in the restriction digest. The isolate also reacted with monoclonal antibodies to Osps A-D, Fla, BmpA (P39), GroEL, DNAk, P22, and P93 (1) . Based on the above observations and tests on this isolate, the spirochete is confirmed to be the B. burgdorferi sensu stricto. Blood, drawn from the dog 7 days after the tick was removed, tested negative to the antibodies of B. burgdorferi at a private laboratory (Diagnostic Veterinary Systems, Don Mills, Ontario). At 21 and 35 days, more blood samples were drawn and sent to the BCCDC. By this time, the dog had seroconverted and both samples were positive with immunofluorescent assay readings of 1:512 and 1:256, respectively. Using Western blot, the latter two blood sera were positive for antigens for OspA-C, P39, flagellin, HSP60, and 66 kDa band. On 24 November 1994, a fully engorged I. scapularis female was removed from a cat in Thunder Bay. This cat had never left the city. PCR testing was used to determine the presence of B. burgdorferi in this dead tick (2) . Although the cat was destroyed before testing for LD, clinical signs indicated possible infection. It had a skin rash (7 cm X 7 cm) at the site of the tick bite on the back of its neck and suffered from lameness, pruritus, renal and bowel dysfunction, and had become very aggressive towards its owner. Up to the end of 1995, 98 locations/occurrences across Ontario have been documented where the black-legged tick has been found with no history of significant travel by the hosts. Eighteen of these were reports of the tick on dogs, cats, birds, and humans in the Thunder Bay District. The first specimen was collected in 1982 from a human (3) . Based on the adult ticks collected from hosts in this area, early questing activity occurs mid-May to mid-July, with fall questing in October and November. Between 1992 and 1995, six adults were collected in the spring and early summer, which is indicative of overwintering. Total annual snowfall in the Thunder Bay area averages 196 cm and apparently provides a suitable microclimate at the soil surface for I. scapularis. The beneficial effect of snowcover was clearly seen in the winter of 1995-96 when the mean air temperature for the period from 19 December to 31 March was -13.9° C (max. + 1.3° C, min. -33.7° C), while the mean temperature at ground level beneath the snow was -0.9° C (max. -0.4° C, min. -2.5° C) (S. Forrester, Department of Biology, Lakehead University: personal communication, 1996). Further studies are needed to determine if all three developmental stages are overwintering in the Thunder Bay area. Endemic areas in Minnesota and Wisconsin provide a source for the black-legged tick, a primary vector of LD. Migratory birds then transport I. scapularis into the Thunder Bay region of Ontario. In the spring of 1995, I. scapularis larvae were removed from an American robin (Turdus migratorius) and a chipping sparrow (Spizella passerina) during bird banding at Thunder Cape on Sibley peninsula (4) . Some ground-frequenting birds and birds carrying immature (larvae or nymphs) ticks act as competent reservoirs for B. burgdorferi. Between 1984 and the end of 1995, a total of 14 LD cases were reported in the Thunder Bay District. Nine had no history of travel. In the same period, a total of 228 cases were reported for all of Ontario (C. LeBer, Public Health Branch, Ontario Ministry of Health: personal communication, 1996). B. burgdorferi has been discovered in individual I. scapularis from several Ontario locations including Kenora (5) , Keewatin, Rainy River, and Point Pelee (2) . As well, it has been found in a beaver tick (I. banksi) at Sault Ste. Marie and a squirrel tick (I. marxi) at Palmer Rapids, Renfrew County (2) . More research is needed to determine if I. banksi and I. marxi are competent vectors capable of transmitting LD spirochetes to animals and humans. References
Source: S Banerjee, PhD, M Banerjee, PhD, Vector-borne Diseases Laboratory, BCCDC, Vancouver, British Columbia; J Scott, BSc(Agr), President, Lyme Disease Association of Ontario, Fergus, M Lankester, PhD, Department of Biology, Lakehead University, Thunder Bay, J Kubinec, DVM, Fort William Animal Clinic, Thunder Bay, Ontario. Editorial Comment The US Centers for Disease Control and Prevention (CDC) received reports of 11,603 cases of LD from 43 states and the District of Columbia in 1995 (overall incidence 4.4 per 100,000 population), the second highest annual number reported since 1982 but an 11% decrease from the 13,043 cases reported in 1994 (1) . As in previous years, the highest numbers of cases were reported from the northeastern, north-central, and mid-Atlantic regions. Personal protection measures (e.g., applying tick repellants and inspecting for ticks) and environmental modifications (e.g., applying insecticides and using deer fencing) will continue to be important methods for reducing the risk of exposure to tick bites and preventing LD and other tickborne diseases (e.g., ehrlichiosis and babesiosis). Human granulocytic ehrlichiosis (HGE) was first described in 1994 (2) among patients in Minnesota and Wisconsin. It is caused by an agent closely related to Ehrlichia equi. The HGE agent has been identified in the deer (I. scapularis) and dog (Dermacentor variabilis) ticks (2) . References
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Last Updated: 2002-11-08 |
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