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

Lyme disease is a serious illness caused by the bacterium Borrelia burgdorferi, which can be spread through the bite of blacklegged ticks. The Public Health Agency of Canada (the Agency), in partnership with provincial and territorial public health authorities, conducts surveillance for Lyme disease in Canada and studies show that the incidence of this disease is on the rise in Canada. Lyme infected ticks are found in many southern regions of Canada and new risk areas are emerging in parts of southern Manitoba, Ontario, Quebec, New Brunswick and Nova Scotia.

The Agency encourages health professionals to learn about Lyme disease and the risk areas in Canada; how to identify the symptoms and apply proper treatment if a patient is diagnosed with the disease; and how to report cases of Lyme through appropriate channels.

On this page:

Lyme disease in humans

At a glance

Lyme disease is a multisystem illness caused by Borrelia burgdorferi, a spirochete transmitted by certain species of Ixodes spp. ticks, specifically the blacklegged tick and the western blacklegged tick. Borrellia burgdorferi causes Lyme disease in humans. The ticks transmit the bacterium to humans after becoming infected by feeding on infected wild animal hosts, such as rodents and birds.

Lyme disease is the most commonly reported vector-borne disease in the northern temperate zone. It became a nationally notifiable disease in December 2009. As such, all healthcare professionals are to report cases of Lyme disease to the Agency via their provincial public health system. The Agency posts information on notifiable diseases on its website.

The Agency currently has data for Lyme disease cases reported between 2009-2012Footnote *:

  • 2009: 128 cases
  • 2010: 132 cases
  • 2011: 258 cases
  • 2012: 315 cases

The incidence of Lyme disease peaks in children between 5-9 years and adults between 55-59 years.

Footnote *
These numbers may change slightly as provincial or territorial public health organisations can from time to time retroactively identify cases. Routine surveillance only gives us part of the picture; the true number of Lyme disease illnesses in Canada is likely much greater.

Lyme disease does not provide long-term immunity; post-treatment re-infection is possible.

Symptomatic infection of the heart is rare in recognized Lyme disease cases, but three sudden cardiac deaths associated with Lyme carditis were reported in the United States in 2012 (MMWR, CDC, Vol. 62, No. 29).External Link

Clinical presentation and course

The clinical manifestations of Lyme disease largely reflect the biology of B. burgdorferi as it replicates in the skin and then disseminates via the bloodstream to other internal sites where disease can be seen (Bockenstedt, p. 283, 2008). Signs and symptoms appear in overlapping stages as early localized disease, early disseminated infection, or late disease.

Know the other clinical manifestations and risk factors, and consider them as part of your differential diagnosis. Accurate diagnosis is one of the key factors to successfully manage Lyme disease.

Image of erythema migrans or EM at the site of a tick bite, as shown here on this woman's upper arm.

Localized Stage - Erythema migrans (EM)

The first and typical symptom of early non-disseminated Lyme disease is usually an expanding rash called erythema migrans (EM).

  • occurs at the site of the infective tick bite within three days to one month post infection (70% - 80% of infected people) and can persist up to eight weeks
  • painless, erythematous skin lesion (≥5 cm in diameter)
  • low-grade fever, fatigue, headache, and arthralgia

Early disseminated disease:

If untreated, the second stage of the disease can last up to several months and include the following symptoms:

  • Neurological (15% - 20% of untreated patients) Bell’s palsy or other cranial neuropathy; meningitis; motor and sensory radiculoneuropathy, mononeuritis multiplex; subtle cognitive difficulties; encephalopathy radiculopathy, cranial neuropathy, and mononeuropathy multiplex)
  • Cardiac (4% - 8% of untreated patients) - conduction abnormalities, e.g. atrioventricular node block; ventricular node block; myocarditis, pericarditis, sudden death)
  • Rheumatological (60% of untreated patients) – Asymetric oligoarticular arthritis, especially involving the knees
  • Cutaneous (multiple EM lesions)
  • Additional manifestations (conjunctivitis, keratitis, uveitis; mild hepatitis; splenomegaly)

Late Lyme disease

If the disease remains untreated, the third stage can last months to years with the following symptoms:

  • Rheumatologic (chronic arthritis, transient, migratory arthritis and effusion in one or multiple joints; migratory pain in tendons, bursae, muscle, and bone; Baker’s cyst; if untreated, arthritis may recur in same or different joints).
  • Neurological (Subacute mild encephalopathy affecting memory and concentration, chronic mild axonal polyneuropathy manifested as distal paresthesias and less commonly, as radicular pain. Rarely, an encephaolomyelitis or leukoencephalopathy may occur.
  • Cardiac (atrioventricular block, myocarditis, pericarditis)

Differential diagnosis

The following should be considered in your differential diagnosis (distinguishing Lyme disease from others presenting with similar signs and symptoms):

  • Ankylosing spondylitis and rheumatoid arthritis
  • AV nodal block
  • Babesiosis, human granulocytic anaplasmosis (HGA), and Rocky Mountain spotted fever (RMSF)
  • Bacterial and viral meningitis
  • Cellulitis, contact dermatitis, and granuloma annulare
  • Chronic fatigue syndrome and fibromyalgia
  • Confusional states and acute memory disorders
  • Gout and pseudogout
  • Prion-related diseases
  • Systematic Lupus Erythematosus (SLE)

(source: Meyerhoff, 2013)


In general, the diagnosis of Lyme disease is  principally clinical, reinforced by a history of tick exposure in an endemic area. Detection of antibodies against B. burgdorferi using the two-tiered testing method described below is an additional diagnostic tool; however acute disease can be diagnosed without laboratory confirmation.

Laboratory testing

Two-tiered testing method

The Agency’s National Microbiology Laboratory (NML) and some provincial laboratories assist clinicians to diagnose Lyme disease using a two-tiered testing method which includes an ELISA screening test followed by a confirmatory Western blot test.

ELISA stands for enzyme-linked immunosorbent assay, which is a blood test that detects the presence of antibodies to Borrelia burgdorferi.

The Western blot also identifies Lyme disease antibodies and can confirm the results of an ELISA test. The NML uses the two-tiered testing method because together the two tests offer more accurate results.

According to the Public Health Agency of Canada, the United States Centers for Disease Control and Prevention and the European Centre for Disease Prevention and Control, the two-tiered method is the best laboratory method currently available for supplementing clinical information on Lyme disease. The two-tiered test starts with a screening ELISA test. Any samples that test positive or equivocal are confirmed using a Western blot test.  This two-tiered approach to blood testing for Lyme disease is based on the best available scientific evidence.

Like other infectious diseases where two-tiered testing is used (for example, HIV infections), screening tests followed by confirmatory tests provide the greatest level of true positives while minimizing the number of false negatives. Simply put, the two-tiered approach provides the most accurate information about infection compared to either test conducted alone. However, all laboratory tests have a margin of error, which is why the Agency recommends that Lyme disease be diagnosed first and foremost on the basis of a doctor’s assessment of symptoms, especially in early infection.

Notes on serologic tests

  • Serologic tests are insensitive during the first few weeks of infection.  During this stage, patients with an EM rash should be diagnosed clinically.  While not necessary, acute and convalescent titers may be helpful in some cases
  • In persons with illness > 1 month, only IgG testing should be performed (not IgM).  A positive IgM test alone is not sufficient to diagnose current disease in these patients
  • Due to antibody persistence, a positive serologic test result cannot distinguish between active and past infection
  • Serologic tests cannot be used to measure treatment response
  • Enzyme immunoassay (EIA) test has low specificity and may yield false-positive results.  They may cross-react with antibodies to commensal or pathogenic spirochetes, some viral infections (e.g., varicella, Epstein-Barr virus), or certain autoimmune diseases (e.g., lupus)

General laboratory findings

  • Elevated erythrocyte sedimentation rate
  • Mildly elevated hepatic transaminases
  • Microscopic hematuria or proteinuria
  • In Lyme meningitis, CSF typically shows lymphocytic pleocytosis, slightly elevated protein, and normal glucose

(Source: U.S. Department of Health and Human Services, 2013)

Laboratory diagnosis

  • Gold standard: culture from affected tissues with confirmation of culture via PCR (but low-sensitivity)
  • Borrelia burgdorferi has been cultured with difficulty.
  • The main method of diagnosis is demonstration of diagnostic IgM or IgG antibodies in serum.  A two-tier testing protocol is recommended – EIA (enzyme immunoassay) should be performed first; if positive or equivocal it is followed by a Western blot assay. Western blot results should be interpreted according to CDC guidelines to obtain the best balance between sensitivity and specificity.
  • Isolation of organism from an appropriate clinical specimen (see IDSA guidelines)
  • In suspected Lyme meningitis, testing for intrathecal IgM or IgG antibodies may be helpful

Canadian laboratory diagnostic guidelines

Canadian laboratory diagnostic guidelines for Lyme disease are consistent with those followed by public health authorities in the United States and Europe and meet international standards.

Public health professionals in these countries have concerns regarding reports of some laboratories that may not be using properly validated tests or criteria for interpreting test results (CDC, MMWR, 2005). Diagnostic methods used by these and Canadian laboratories produce a similar number of positive results, indicating that patients have been exposed to Lyme disease bacteria. However, the methods used by some laboratories may detect more “false positives” in people who are actually not infected with Lyme disease. As a result, patients who do not have Lyme disease may end up receiving potentially harmful treatments.


Treatment regimens listed in the following table are for localized (early) Lyme disease. Treatment guidelines for patients with disseminated (late) Lyme disease are outlined in the reference below (Wormser, et al., 2006).

These regimens are guidelines only and may need to be adjusted depending on a patient’s age, medical history, underlying health conditions, pregnancy status or allergies.  Consult an infectious disease specialist for the most current treatment guidelines or for individual patient treatment decisions.

Age Category Drug Dosage Maximum Duration in Days(Range)
Adults Doxycycline 100 mg, p.o., q 12 h. N/A 14 (14-21)
Cefuroxime axetil 500 mg, p.o., q 12 h N/A 14 (14-21)
Amoxicillin 500 mg, p.o., q 8 h N/A 14 (14-21)
Children Amoxicillin 50 mg/kg per day p.o., divided in 3 doses 500 mg per dose 14 (14-21)
Doxycycline 4 mg/kg per day p.o., divided into 2 doses 100 mg per dose 14 (14-21)
Cefuroxime axetil 30 mg/kg per day p.o., divided into 2 doses 500 mg per dose 14 (14-21)


  1. For patients intolerant of amoxicillin, doxycycline, and cefuroxime axetil, the macrolides azithromycin, clarithromycin, or erythromycin, may be used, although they have lower efficacy.  Patients treated with macrolides should be closely observed to ensure resolution of clinical manifestations.
  2. Doxycycline is contraindicated in children younger than 8 years of age and in pregnant or lactating women. Amoxicillin is the drug of choice for children younger than 8 years of age and pregnant or lactating women.

Although timely treatment with a recommended two- to four-week course of antibiotics is effective to treat Lyme disease in most cases, approximately 10 to 20 per cent of Lyme disease patients have persistent symptoms of fatigue, pain, or joint and muscle aches following treatment. Research continues into the causes of persistent symptoms and the effectiveness of long-course antibiotic treatment.  

Lyme disease in pregnancy

A few early case reports of pregnant women with untreated Lyme disease described adverse outcomes, with babies stillborn or dying within 48 hours of birth, but no set pattern of abnormality was found.  Subsequent large population studies showed no increased risks of adverse outcomes of pregnancies in women with Lyme disease who received appropriate treatment, and large population studies of pregnancy outcomes in Lyme high-endemic areas and non-endemic areas showed no excess of adverse outcomes in high-endemic areas (O’Connell, 2011).


There is no vaccine for Lyme disease. The best way to avoid Lyme disease is to protect against tick bites. Health professionals should advise their patients to take the following measures:

  • If there are ticks in your area, cover up if you think you might be exposed to them. Wear closed-toe shoes, long-sleeved shirts and pants. Pulling your socks over your pant legs prevents ticks crawling up your legs. Light-coloured clothing makes spotting ticks easier.
  • Use insect repellents that contain DEETExternal Link (concentration between 20-30%) or Icaridin. Repellents can be applied to clothing as well as exposed skin. Always read and follow label directions.
  • Shower or bathe within two hours of being outdoors. Daily “full body” checks for ticks should be performed: ticks attach themselves to the skin so they can be found and removed, which usually prevents infection if this is done early enough (within 24-48 hours). Be sure to check children and pets for ticks as well.


The Agency works with the provinces, health authorities and other experts to define and monitor the occurrence of the ticks that carry Borrelia burgdorferi.

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). Knowledge of whether a patient has had exposure to these areas is important for Lyme disease diagnosis and reporting of Lyme disease cases.

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 parts 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.
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 The ”South East Corner” population comprising an area adjoining the western shore of Lake of the Woods, including Moose Lake Provincial Park. Known endemic
The “Pembina” population within an area along the Pembina valley and Pembina escarpment extending from the American border to South Norfolk in the north and west to Killarney. This includes Pembina Valley Provincial Park. Known endemic
The “Vita/Arbakka” population within which ticks occur in small and isolated forests, particularly along the Roseau River. Suspect area
The “Eastern Assiniboine” population extending from Beaudry Provincial Park westward along the Assiniboine River as far as Poplar Point. Suspect area
The “St. Malo” population comprising two groups, one in the Kleefeld area, west of Steinbach and the other in the St. Malo/Roseau River area. Suspect area
The “Richer/Ste. Genevieve Population” adjacent to the Agassiz and Sandilands provincial forests. 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 Millidgeville area of Saint John Known endemic
North Head, Grand Manan Island Known endemic
Nova Scotia Areas of Lunenburg County Known endemic
Areas of Halifax Regional Municipality Known endemic
Areas of Shelburne County Known endemic
Areas of Yarmouth County Known endemic
Areas of Pictou County Known endemic
Areas of Queens County Known endemic

New areas at risk from Lyme disease in Canada

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 diagnose infections. Note that the Agency recommends that Lyme disease is diagnosed primarily on clinical criteria, with support, where possible, from laboratory tests.

Figure 1. The locations where the risk from tick bites and Lyme disease is known to occur, and where risk of tick bites and Lyme disease is possible. Locations where ticks and Lyme disease risk are known are called ‘endemic areas’ (‘known’ endemic areas if ticks and Lyme disease risk have been confirmed over several years of field study or by the occurrence of multiple human cases, otherwise they are called ‘suspect’ endemic areas). Also shown are hatched areas where surveillance and research studies suggest areas where ticks and Lyme disease risk have begun to become established.

Figure 1

Text equivalent for Figure 1

Larger version of Figure 1

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 siteExternal Link. Lyme disease also occurs in Europe and some parts of AsiaExternal Link.

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 of coming 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 of Lyme disease cases and endemic areas

PHAC is engaged in two forms of surveillance for Lyme disease: surveillance of Lyme disease human cases, and surveillance for ticks.

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

  • 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).
  • 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

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

The Agency currently has data for Lyme disease cases reported between 2009-2012Footnote *:

  • 2009: 128 cases
  • 2010: 132 cases
  • 2011: 258 cases
  • 2012: 315 cases
Footnote *
These numbers may change slightly as provincial or territorial public health organisations can from time to time retroactively identify cases.

Although the Agency conducts surveillance both on ticks carrying the bacteria that causes Lyme disease and on human cases of Lyme disease, surveillance detects only a portion of the Lyme disease cases in Canada. The true number of Lyme disease illnesses in Canada is likely much greater.

This is also true in the United States (US). Each year, approximately 30,000 cases of Lyme disease are reported by the Centers for Disease Control and Prevention (CDC); however this number does not reflect every case of Lyme disease. The CDC estimates that approximately 300,000 people are diagnosed with Lyme disease each year in the US. For additional information, please visit the CDC’s websiteExternal Link.

The Agency relies on the provinces and territories to report the number of Lyme disease cases occurring in their jurisdictions on an annual basis. In order to most accurately reflect the occurrence of Lyme disease cases in Canada each year, healthcare professionals need to remain vigilant in diagnosing early in the course of the disease and reporting cases to their public health regional authorities.

Lyme disease endemic areas

TPHAC 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 assess 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 ColumbiaExternal Link(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.

Figure 2

Text equivalent for figure 2 A map showing areas predicted to be at risk for emergence of Lyme endemic areas in eastern and (inset) central Canada. A 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. 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 green zone indicates the main extent of locations where Lyme endemic areas may emerge. The orange and red zones indicate areas with increasingly high risk for emergence of new Lyme endemic areas. 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, Borrelia carolinensis and Borrelia kurtenbachii although whether these bacterium cause disease in humans in North America is unknown. The bacterium Borrelia miyamotoi occurs at low prevalence in blacklegged ticks and recently human cases (mostly suffering influenza-like illnesses) associated with B. miyamotoi have been discovered in the U.S., and vigilance by physicians for cases associated with this bacterium is recommended.

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 ascends beginning in the legs and spreads 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 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.

Unfed adult blacklegged ticks

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.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.

Life stages of the blacklegged tick

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.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.

Female blacklegged ticks in various stages of feeding

Text equivalent for 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.

Unfed, partially fed and fully engorged nymphs of the blacklegged tick

Text equivalent for 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 other analyses. These ticks assist in our surveillance for new emerging Lyme disease risk locations.

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 small piece of paper towel placed inside the container will protect the tick from being damaged during shipment. 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 professional 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

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 extend to 4-6 weeks because of the large volume of tick samples received.

How to download PDF documents:
Please download the document by right clicking on the link below and choose: "Save Target As" or "Save Link As"

Please follow the guidelines for handling and shipping ticks and complete and attach a Tick Submission Form (PDF Document - 766 KB - 1 page) with the submission.

If you do not have PDF viewing software, you can download a free PDF viewer from the Adobe® Web siteExternal link.


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