Lyme disease and other tick-borne diseases: Information for health professionals

The Public Health Agency of Canada (PHAC) works with the provinces, health authorities and other experts on research to define and monitor the occurrence of the ticks that carry Borrelia burgdorferi, the bacterium that causes Lyme disease. In Canada, the blacklegged tick (Ixodes scapularis; often referred to as a 'deer tick') and the western blacklegged tick (Ixodes pacificus) are the species that most commonly transmit this disease causing agent, as well as other less common agents. Other tick species are known to transmit Lyme disease in nature but these ticks rarely bite humans. The greatest risk of Lyme disease in Canada occurs where populations of these ticks are established, and where there is evidence that these established ticks are transmitting the agent of Lyme disease. These locations are termed ‘Lyme endemic areas’ as defined by Health Canada (1991).

Established Tick Populations in Canada

Our current knowledge of the occurrence of established tick vectors, based on active surveillance in the field, is detailed in Table 1 and Figure 1. This distribution suggests that tick populations and Lyme endemic areas currently occur in a limited area of Canada; however surveillance indicates that established populations of blacklegged ticks are spreading their geographic scope, and are increasing in number, in much of southern Canada. The potential expansion of localized tick populations makes it difficult to precisely define the geographic limits of any given population; however people living or visiting areas adjacent to established tick populations may have a greater chance of contact with blacklegged ticks.

Table 1. Known and suspected Lyme endemic areas in Canada. Definitions for known and suspected endemic areas can be found in the surveillance section of this web page.

Province	Approximate Location	Status
Lyme disease risk where the western blacklegged tick is the vector
British Columbia	Southern mainland, Vancouver Island	Known endemic in some areas, suspected over a wider region
Lyme disease risk where the blacklegged tick is the vector
Manitoba	Restricted region of western shore of Lake of the Woods	Known endemic
	Parts of the Stanley Trail/Thompson Trail	Known endemic
	The area around Pembina Valley Provincial Park	Known endemic
	Locations in the Pembina Valley	Suspect area
	St. Malo area	Suspect area
	Arbakka area	Suspect area
	Beaudry Provincial Park	Suspect area
Ontario	Point Pelee National Park	Known endemic
	Rondeau Provincial Park	Known endemic
	Turkey Point Provincial Park	Known endemic
	Long Point peninsula including Long Point Provincial Park and the National Wildlife area	Known endemic
	Wainfleet bog region near Welland	Known endemic
	Prince Edward Point	Known endemic
	Parts of the Thousand Islands National Park	Known endemic
Quebec	Montérégie	Five known endemic areas
New Brunswick	Northern St John area	Known endemic
	North Head, Grand Manan Island	Known endemic
Nova Scotia	Lunenburg County (Blue Rocks, Garden Lots, Heckmans Island, First Peninsula as well as the areas immediately surrounding them)	Known endemic
	Halifax County: Admirals Cove in Bedford;	Known endemic
	Shelburne County: Gunning Cove	Known endemic
	Gavelton near Yarmouth	Known endemic
	Pictou county areas around Melmerby Beach, Egerton, Kings Head, and Pine Tree	Known endemic

Identifying areas at risk from new Lyme endemic areas

The establishment of new tick populations is an ongoing process, so it is desirable to continue surveillance to continuously update our knowledge of where Lyme disease risk occurs in Canada. With this information, public health professionals can target preventive advice and control efforts to the people and places most in need and members of the public who may be particularly at risk from Lyme disease due to their geographic location and/or occupation (e.g. forester, park worker) or choice of leisure activity (camping, golfing, etc.). These people can then be provided with the information they need to prevent infection and obtain prompt treatment if they do become infected. In addition, knowledge of where Lyme endemic areas occur in Canada allows healthcare professionals to decide whether or not patients have been exposed to a Lyme endemic area, which in turn will influence the weight of evidence needed to diagnoses infections. Note that the PHAC recommends that Lyme disease is diagnosed on clinical criteria with support, where possible, from laboratory tests. Details on clinical diagnosis and treatment for healthcare professionals can be obtained from Wormser et al., 2006 .

Figure 1. A map showing locations of known (red triangles) and suspected (blue triangles) Lyme endemic areas in eastern and (inset) central Canada.

Text equivalent for figure 1A map showing locations of known (red triangles) and suspected (blue triangles) Lyme endemic areas in eastern and (inset) central Canada.

Larger version of Figure 1 A map showing locations of known (red triangles) and suspected (blue triangles) Lyme endemic areas in eastern and (inset) central Canada.

Visitors to the United States (USA) should note that there are extensive areas with established blacklegged tick populations there, particularly in the northeast and upper Midwest regions. More information on Lyme in the USA can be found on the Centers for Disease Control and Prevention web site . Lyme disease also occurs in Europe and some parts of Asia .

The proportion of ticks infected with the bacterium causing Lyme disease varies. The proportion infected is typically higher in adult ticks compared to the other stages (nymphs and larvae). However, people are most likely to acquire Lyme disease from a nymph because this stage is so small (see Figure 4) and thus more likely to go unnoticed and feed for a sufficient amount of time for the Lyme disease bacterium to be transmitted (24-36 hours). The proportion of ticks infected is often greater in tick populations that have been established for long periods of time (such as Long Point) compared to newly established ones. As many as 60% of the adult ticks at Long Point are infected; however, infection rates in adults are more often between 10 and 25% at the other localities where ticks are established. Partly because of differences in the types of hosts that they feed upon, the proportion of I. pacificus ticks that are infected with the Lyme disease agent is usually much lower (1-3%) than the proportion of I. scapularis ticks that are infected.

While there is a higher risk to come in contact with infected blacklegged ticks in areas where populations are established, there is also a low risk of Lyme disease being contracted almost anywhere in Canada because migratory birds transport infected ticks over large geographic distances. Surveillance data indicates that about 10% of these so-called ‘adventitious’ ticks detected outside of areas where tick populations are established, and likely transported there on migratory birds, are infected with the agent of Lyme disease.

Surveillance for Lyme disease and the ticks that transmit Lyme disease.

PHAC is engaged in two forms of surveillance for Lyme disease: surveillance for Lyme disease cases and surveillance to assist Provincial and Territorial public health organisations in identifying Lyme disease risk areas before human Lyme disease case occur.

Surveillance for cases of Lyme disease in Canadians.

Since December 2009 Lyme disease is a nationally notifiable disease in Canada. This means that all cases that fit the surveillance case definition criteria should be notified by healthcare professionals to the local medical officer of health. The case definition comprises confirmed and probable classifications:

Confirmed cases

1. Clinical evidence of illness with laboratory confirmation by isolation of Borrelia burgdorferi from an appropriate clinical specimen, or by detection of B. burgdorferi deoxyribonucleic acid (DNA) by Polymerase Chain Reaction (PCR).
2. Clinical evidence of illness with a history of residence in, or visit to, an endemic area and with laboratory evidence of infection by approved serological methods and test interpretations.

Probable cases

1. Clinical evidence of illness without a history of residence in, or visit to, an endemic area and with laboratory evidence of infection.
2. Clinician-observed EM without laboratory evidence but with history of residence in, or visit to, an endemic area.

For additional details, please view the Agency’s Canada Communicable Disease Report – November 2009.

Surveillance for Lyme disease endemic areas

The PHAC works with Provincial and Territorial public health organisations to perform surveillance that aims to identify Lyme disease risk areas so that we can prevent Lyme disease cases before they occur. One method is ‘passive’ surveillance for tick vectors of Lyme disease, which involves surveillance for ticks found on humans and domestic animals that are submitted voluntarily by veterinarians and healthcare professionals (Ogden et al., 2006; 2010). This method can raise the suspicion of areas where ticks are establishing. The second method is ‘active’ field surveillance to collect ticks and/or wild animal hosts from suspect areas to determine whether populations of vector ticks and endemic cycles of Borrelia burgdorferi transmission have become established, which is the method by which the occurrence of a Lyme disease endemic area is confirmed (Health Canada 1991).

A confirmed Lyme disease endemic area is defined as a locality where active surveillance has detected i) reproducing populations of the tick vector as confirmed by the presence of all three stages (larva, nymph and adult) on resident animals or in the environment for at least 2 consecutive years; and ii) the agent of Lyme disease (B. burgdorferi) in ticks and/or wild animal hosts collected from the locality as evidenced by culture, molecular methods (specific PCR) or immunofluorescent antibody staining (IFA).

A suspected Lyme disease endemic area is a locality where active field surveillance has revealed the presence of multiple ticks at one or more visits suggesting that the tick vector is becoming established, and where B. burgdorferi has been detected in ticks or animals collected from the site.

Field surveillance for ticks cannot cover the whole of Canada because of the immensity of our country, and because of the practical difficulties in performing surveillance in remote areas and on privately held land. In collaboration with provincial public and animal health organisations, and with Canadian Universities, the Agency has developed a map (Figure 2) to show where establishment of new blacklegged tick populations, and subsequently Lyme endemic areas, is most likely to be occurring. The objectives of this map are to help guide surveillance and preventative efforts by public health professionals, and to provide a resource for those working and participating in leisure activities in the outdoors to asses whether or not they should contact the local provincial or territorial public health organisations for specific information on Lyme disease risk in their region. The map is constructed using the Agency’s current knowledge of the biology of the blacklegged tick and of the environmental factors that limit its survival (Ogden et al., 2008), and has performed well in field validation to date (Ogden et al., 2008; 2010).

Please click here for a risk map produced by the British Columbia Centre for Disease Control for the occurrence of Lyme endemic areas in British Columbia (Mak et al., 2010).

Figure 2. A map showing areas predicted to be at risk for emergence of Lyme endemic areas in eastern and (inset) central Canada.

Text equivalent for figure 2A map showing areas predicted to be at risk for emergence of Lyme endemic areas in eastern and (inset) central Canada.

Larger version of Figure 2 A map showing areas predicted to be at risk for emergence of Lyme endemic areas in eastern and (inset) central Canada.

The coloured zones on the map indicate current predictions for regions where Lyme endemic areas are most likely to emerge provided that suitable woodland habitat for the blacklegged tick exists. The yellow zone indicates the main extent of locations where Lyme endemic areas may emerge. The orange zone indicates areas with a particularly high risk for emergence of new Lyme endemic areas, while the green zone indicates areas where the risk of Lyme endemic areas emerging is possible but low. The grey zone indicates areas where in general the risk of Lyme endemic area emergence is predicted to be very low and risk of Lyme disease is mostly restricted to that posed by ‘adventitious’ ticks dispersed by migratory birds from Lyme endemic areas in Canada and the USA. Even so, in some localised areas of the grey risk zone, local environmental conditions may be suitable for Lyme endemic areas to emerge.

Other tick-borne diseases in Canada

Both the blacklegged tick and western blacklegged tick transmit pathogens other than the agent of Lyme disease. These pathogens are all zoonoses (i.e. infections of animals that can cause disease in humans) for which the natural hosts are wild animals. Of importance are the bacterium Anaplasma phagocytophilum, which causes Human Granulocytic Anaplasmosis (HGA: Wormser et al., 2006), the protozoal parasite Babesia microti, which causes human babesiosis, and Powassan encephalitis virus (POWV), a rare cause of encephalitis. Other bacteria carried by these ticks include Borrelia bissettii, and Borrelia miyamotoi although whether these bacterium cause disease in humans in North America is unknown.

Tick-borne diseases transmitted by other tick species also occur in Canada and include Rocky Mountain Spotted Fever (caused by Rickettsia rickettsii) transmitted primarily by the Rocky Mountain wood tick (Dermacentor andersoni) and Tularaemia (caused by the bacterium Francisella tularensis:) transmitted by the American dog tick(Dermacentor variabilis Figure 2), Powassan encephalitis caused by Powassan virus (POWV) transmitted by Ixodes cookei ticks and relapsing fever (caused by the bacterium Borrelia hermsii) which is transmitted by soft bodied (Argasid) ticks in southern British Columbia. Tick-borne diseases carried by the ‘Lone Star tick’ Amblyomma americanum, which include Human Monocytic Ehrlichiosis caused by the bacterium Ehrlichia chaffeensis could also occur rarely in Canada associated with ticks dispersed from the USA by migratory birds.

A toxin in the saliva of adult female Rocky Mountain wood ticks (RMWT) can cause paralysis in humans and animals on which these ticks feed. Paralysis is ascending beginning in the legs and spreading to other muscles during the period the tick is feeding. Paralysis can extend to muscles important for respiration, and if not diagnosed and treated early the paralysis can result in death. Simple removal of the feeding ticks is usually sufficient for recovery to occur (Gregson, 1973). Rocky Mountain wood ticks are found from central Saskatchewan to British Columbia although RMWT in the Canadian prairies may be genetically incapable of causing paralysis (Lysyk, 2010).  Other tick species endemic to Canada such as American dog ticks and blacklegged ticks have been linked to cases of tick paralysis but not in Canada (Gregson 1973).

Identifying Ticks

Blacklegged Ticks

Blacklegged ticks are considerably smaller than the more common American dog tick (often called the wood tick), Dermacentor variabilis.  Adults of the blacklegged ticks lack the white marking seen on the dorsum of adult dog ticks (Figure 3). Before feeding, blacklegged adult females are approximately 3-5 mm in length and red and dark brown in colour. The pre-adult stages (larvae and nymph) are much smaller and lighter in colour (Figure 4). All stages except adult males increase in size and change colour as they feed upon a host. For example, it is not uncommon for adult females to reach the size of a small grape and they typically go through a change in colour from whitish as they start feeding to dark gray to nearly black when fully fed (Figure 5). Larvae and nymphs also increase proportionally in size and go through a similar change in colour (Figure 6).

Figure 3: Unfed adult blacklegged ticks (top row) and adult American dog (wood) ticks (bottom row). Note the difference in colour patterns and relative size.

Text equivalent for figure 3 Unfed adult blacklegged ticks (top row) and adult American dog (wood) ticks (bottom row). Note the difference in colour patterns and relative size.

Figure 4: Unfed life stages of the blacklegged tick (1-larva, 2-nymph, 3-adult male, 4-adult female). Sizes presented in relation to underlying 10-cent coin.

Text equivalent for figure 4 Life stages of the blacklegged tick (1-larva, 2-nymph, 3-adult male, 4-adult female). Sizes presented in relation to underlying 10-cent coin.

Figure 5: Female blacklegged ticks in various stages of feeding. Note the change in size and colour.

Text equivalent for figure 5 Female blacklegged ticks in various stages of feeding. Note the change in size and colour.

Figure 6: Unfed, partially fed and fully engorged nymphs of the blacklegged tick. Note the change in size and colour.

Text equivalent for figure 6 Unfed, partially fed and fully engorged nymphs of the blacklegged tick. Note the change in size and colour.

Submitting Ticks for Identification and Testing

PHAC scientists, in collaboration with provincial and territorial colleagues, have been studying the distribution of the blacklegged tick since the early 1990s. The information gathered from these studies helps to determine the current range of this tick in Canada and to better define the areas of risk of human exposure to infected blacklegged ticks.

Ticks collected by members of the general public, veterinarians, healthcare professionals and wildlife biologists from pets, people, or wild animals can be submitted for identification and testing. This passive surveillance helps to identify areas for further research.

To remove ticks that are embedded in skin, use tweezers to carefully grasp the tick as close to the skin as possible and pull slowly upward, avoiding twisting or crushing the tick. Do not try to burn or smother the tick. Cleanse the bite area with soap and water, alcohol or household antiseptic. Note the date and location of the bite and save the tick in a secure container such as an empty pill vial or film canister. A bit of moistened paper towel placed inside the container will keep ticks from drying out. Dried out ticks are more difficult to identify and test for infection. If members of the public are concerned about removing a tick from themselves or a member of their family, it is advisable that they ask for assistance from a healthcare professionals, who can also advise on possible symptoms of tick-borne diseases to permit early recognition of infection and prompt treatment. Similarly local veterinarians will be able to remove ticks from pets and advise on any treatments they may require.

When possible, ticks should be sent to provincial collaborators who will identify the tick and then forward only the blacklegged ticks to the Agency's National Microbiology Laboratory (NML). Staff at the NML will conduct diagnostic testing for the Lyme disease agent as well as several other disease-causing agents. For information on where to send tick specimens in your area, contact the NML through phone or email at:

National Microbiology Laboratory
Phone: (204) 789-2000
Email: ticks@phac-aspc.gc.ca

Please note that it usually takes at least two weeks for ticks submitted to the NML to be identified, tested, and for results to be reported to the original submitter. During the peak periods of adult activity (October to December), the processing time at the NML can extent to 4-6 weeks because of the large volume of tick samples received.

References:

Gregson, J. D. 1973. Tick paralysis: an appraisal of natural and experimental data. Monograph No.9. Agriculture Canada.

Health Canada. 1991. Consensus conference on Lyme disease. CMAJ 144:1627-1632.

Lysyk TJ. 2010. Tick paralysis caused by Dermacentor andersoni (Acari: Ixodidae) is a heritable trait. J Med Entomol. 47:210-214.

Mak, S., Morshed, M. and Henry B. 2010 Ecological niche modeling of Lyme disease in British Columbia, Canada. J Med Entomol. 2010 47(1):99-105.

Ogden, N.H., St. Onge, L., Brazeau, S., Lindsay, L.R., Barker, I.K., Bigras-Poulin, M., Charron, D.F., Heagy, A., Francis, C.M., Maarouf, A., O'Callaghan, C.J. & Thompson, R.A. 2008. Risk maps for range expansion of the Lyme disease vector, Ixodes scapularis, in Canada now and with climate change. Int. J. Health Geogr. 7:24.

Ogden, N.H., Bouchard, C., Kurtenbach, K., Margos, G., Lindsay, L.R., Trudel, L., Nguon, S. & Milord F. 2010. Active and passive surveillance, and phylogenetic analysis of Borrelia burgdorferi elucidate the process of Lyme Disease risk emergence in Canada. Environ Health Perspect. Mar 25. [Epub ahead of print]

Wormser GP, Dattwyler RJ, Shapiro ED, Halperin JJ, Steere AC, Klempner MS, Krause PJ, Bakken JS, Strle F, Stanek G, Bockenstedt L, Fish D, Dumler JS, Nadelman RB. 2006. The clinical assessment, treatment, and prevention of lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 43:1089-134.