Updated May 2019

Lyme disease in humans is caused by three species of Borrelia bacteria. In North America, Lyme disease is caused primarily by Borrelia burgdorferi, while in Europe the disease is caused mainly by B. garnii and B. afzelli. In Ontario, transmission occurs through the bite of infected blacklegged ticks called Ixodes Scapularis or deer ticks.

The overall risk of acquiring Lyme disease in Toronto is low but is increased if doing activities in wooded and bushy areas in eastern parts of Toronto.

For Lyme disease clinical guidance refer to the Management of Tick Bites and Investigation of Early Localized Lyme Disease Algorithm.

  • Note: The City of Toronto has a prevalence of ticks infected with Borrelia burgdorferi greater than 20 per cent and therefore meets the criteria for consideration of post-exposure prophylaxis.

Signs and symptoms usually occur one to two weeks after a tick bite but can begin as early as three days to as long as four weeks after a tick bite.

Lyme borreliosis is generally divided into three stages in which infected persons may experience any of the following symptoms:

Early Localized Disease Early Disseminated Disease Late Disease
  • erythema migrans (EM) or bull’s eye rash (see below) at the site of a recent tick bite
  • fever
  • malaise
  • headache
  • myalgia
  • neck stiffness
  • fatigue
  • arthralgia
  • multiple EM in approximately 15 per cent of people occurs several weeks after infective tick bite
  • cranial nerve palsies
  • lymphocytic meningitis
  • conjunctivitis
  • arthralgia
  • myalgia
  • headache
  • fatigue
  • carditis
May develop in people with early infection that was undetected or not adequately treated. May involve the following:

  • heart
  • nervous system and joints
  • arrhythmias, heart block and sometimes myopericarditis
  • recurrent arthritis affecting large joints (i.e., knees)
  • peripheral neuropathy
  • central nervous system manifestations – meningitis; encephalopathy (i.e., behavior changes, sleep disturbance, headaches)
  • fatigue

Erythemas Migrans (Bull’s-Eye Rash)

2 examples of bull's eye rashes.
Lyme Disease Erythema Migrans

EM represents a response to the bacterium as it spreads intradermally from the site of the tick bite. Characteristics include:

  • Develops in about 70 to 80 per cent of infected persons.
  • Occurs within three to 30 days (average seven days) at the bite site; can persist for up to eight weeks.
  • The rash gradually expands and can reach up to 30 cm across its largest diameter. As it expands, area of the rash may clear resulting in a bull’s-eye appearance.
  • Rash is rarely itchy or painful; usually feels warm to the touch.

Note: An erythematous skin lesion that presents while a tick is still attached or which develops within 48 hours of detachment is most likely a hypersensitivity rather than EM.

  • Tick bite hypersensitivity is typically less than five cm in largest diameter, has urticarial appearance and begins to disappear within 24 to 48 hours.
  • There is usually little pain, swelling, itchiness, scaling, exudation or crusting, erosion or ulceration.
  • Inflammation at the centre of the lesion may or may not be present.

In Ontario, blacklegged ticks are the only type of tick that transmits the bacteria that causes Lyme disease.

  • The risk of human infection increases with the time a tick is attached to a person and usually requires the tick to be attached for 24 hours or more.
  • Ticks can attach to any part of the human body but, if found, may be in hard-to-see areas such as the armpits, groin and scalp.
  • Most humans are infected through the bites of immature ticks called nymphs, which are tiny (less than two mm) and difficult to see.
  • Adult ticks can also transmit Lyme disease bacteria, but they are larger (five mm) and therefore more likely to be discovered and removed before they have had time to transmit the bacteria.
  • Early detection and removal of ticks is important in the prevention of Lyme disease.

Knowledge of a patient’s exposure to Lyme disease risk areas is an important parameter for Lyme disease diagnosis.

  • Tick populations continue to expand and it is possible that Lyme disease can be acquired outside the currently identified areas.
  • Ticks can travel or migrate on the bodies of animals such as birds, and therefore can be sporadically present in very low numbers over an even broader area.

Diagnosis, particularly the early stage, is based primarily on clinical symptoms and epidemiological risk factors.

Public Health Ontario Laboratory has information on Lyme disease serology.

  • PHO performs a two-step testing protocol for Lyme disease for Lyme to detect antibodies against B. burgdorferi.
    • Blood sample should be collected in a red-top tube and sent to Public Health Ontario Laboratory.
    • The first step involves testing using a screening Enzyme Immunoassay (EIA) test.
    • If initial EIA result is non-reactive, healthcare providers should consider an alternative diagnosis; or in cases where the patient has had symptoms for less than or equal to 30 days, the provider may treat the patient and follow up with a convalescent serum.
    • If the EIA result is reactive or indeterminate, a confirmatory test using Western Immunoblot assay is performed.
  • Blood tests may be negative in patients with early-stage Lyme disease or in patients previously treated with antibiotics.
  • The accuracy of blood tests increases as the infection progresses, although it is recognized that a small proportion of patients with later-stage Lyme disease may test negative.
  • The stage of infection and the possible impact of treatment on the outcomes of blood testing should be taken into consideration during diagnosis.

If a patient was exposed to other species of Borrelia such as those that occur in Europe:

  • Provide travel history and request testing for European Lyme disease.
    The specimens from these patients are sent to the National Microbiology Laboratory for antibody testing.

For information on preventing Lyme disease, please visit Toronto Public Health’s Environmental Health Lyme disease prevention page.

Ticks must be collected in a clean transparent container.  Name of the patient and date of birth must be marked on the container. A sterile urine collection container may be used for this purpose.

  • All ticks submitted for testing must be accompanied by the Surveillance Form for Tick Identification (Public Health Ontario)
  • Ticks must be couriered or delivered to:

Parasitology Laboratory, Public Health Ontario
MaRS 2 Tower (south side)
661 University Avenue
Toronto, Ontario M5G 1M1

To assist with Toronto Public Health’s (TPH) passive surveillance activities, please remember to fax the submission form to 416-392-0714, attention Vector Borne Disease Manager or call TPH for tick submission assistance at 416-338-7600.

More information:

For Lyme disease clinical guidance refer to the Management of Tick Bites and Investigation of Early Localized Lyme Disease Algorithm.

  • Note: The City of Toronto has a prevalence of ticks infected with Borrelia burgdorferi greater than 20 per cent and therefore meets the criteria for consideration of post-exposure prophylaxis.

A single dose of oral doxycycline may be offered to patients of any age when all of the following conditions are met:

  1. Adult or nymph of I. scapularis tick was attached for more than 24 hours; and
  2. Prophylaxis can be started within 72 hours from the time that the tick was removed: and
  3. Person was exposed in an area where ecologic information indicates that the rate of infection of ticks is greater than 20 per cent. This applies to the City of Toronto, and
  4. Doxycycline treatment is not contraindicated

There is effective antibiotic treatment for early localized Lyme disease. Should prophylaxis not be indicated based on the above criteria, the health care provider should watch for signs and symptoms of Lyme disease and treat early.

For more information on the prevention and treatment of Lyme disease see the full guidelines developed by the Infectious Diseases Society of America (2006).

Post-treatment Lyme Disease Syndrome (PTLDS)

Approximately 10 to 20 per cent of patients may experience persistent or recurrent symptoms following appropriate antibiotic treatment, and are considered to have Post-treatment Lyme Disease Syndrome.