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Lyme Disease

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Reporting Obligations

Individuals who have or may have lyme disease shall be reported to the local Health Unit.

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Aetiologic Agent

Lyme disease is a tick-borne zoonotic disease caused by the bacterium, Borrelia burgdorferi (B. burgdorferi), a spirochete first identified in North America in 1982.

Clinical Presentation

Lyme borreliosis is generally divided into 3 stages in which infected persons may experience any of the following symptoms:

Early localized disease:

  • Erythema migrans (EM) or “bull’s eye” rash at the site of a recent tick bite, fever, malaise, headache, myalgia, neck stiffness, and arthralgia. EM is defined as a skin lesion that typically begins as a red macule or papule and expands over a period of days to weeks to form a round or oval expanding erythematous area ≥5 cm in size across the diameter. It appears 1–2 weeks (range 3–30 days) after infection and persists for up to 8 weeks (see EM pictures).

Early disseminated disease:

  • Multiple erythema migrans in approximately 15% of people occurs several weeks after infective tick bite, cranial nerve palsies, lymphocytic meningitis, conjunctivitis, arthralgia, myalgia, headache, fatigue, carditis (heart block).

Late disease:

  • May develop in people with early infection that was undetected or not adequately treated. Involves the 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); and fatigue.

Modes of Transmission

Bite by a black legged tick carrying B. burgorferi bacteria that has been attached for at least 24 hours.

Incubation Period

For early localized disease, from 3–30 days after tick exposure with a mean of 7–10 days; early stages of the illness may not be apparent and the person may present with later manifestations.

Period of Communicability

There is no evidence of person to person spread.

Risk Factors/Susceptibility

Persons with history of tick bites in an area where ticks carry the B. burgdorferi bacteria, Ontario Lyme disease Risk Areas Map 2019.

Occupations/activities in tall grass or wooded areas where ticks reside.

Post-exposure prophylaxis can be considered if four criteria are met as outlined in the Clinical Guidance Document, Management of Tick Bites and Investigation of Early Localized Lyme Disease.  

Diagnosis and Laboratory Testing

Diagnosis is based on clinical and epidemiological findings. Lab testing is used to support clinical suspicion of early and late disseminated Lyme disease. Serological evidence using the two-tier enzyme linked immuno-sorbent assay (ELISA) and Western Blot criteria is used to support clinical diagnosis of Lyme Disease.

Indications and Limitations

  • When patients are treated very early in the course of illness, antibodies may not develop.
  • If serological testing was done for early localized disease initial negative serological tests in patients with skin lesions suggestive of EM should have testing repeated after 2–4 weeks, however if patients are treated during this time, subsequent testing may be negative.
  • The Western blot (particularly only IgM reactivity) may yield a false positive result.
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Treatment and Case Management

Treatment is under the direction of the attending health care provider.

Lyme disease treatment guidelines are available from the Anti-infective guidelines for Community-acquired Infections (“Orange Book” by the Anti-infective Review Panel) or the Canadian Communicable Disease Report, Lyme disease: clinical diagnosis and treatment, 2014, which includes 2006 clinical practice guidelines by the Infectious Diseases Society of America.

The Clinical Guidance Document, Management of Tick Bites and Investigation of Early Localized Lyme Disease also includes information on laboratory testing and recommendations for treatment of patients with early localized lyme disease.

Patient Information

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Additional Resources

Public Health Ontario. “Lyme Disease.”

Public Health Agency of Canada. CCDR Report May 29, 2014, “Clinical aspects of Lyme disease.”

Ministry of Health and Long-Term Care “Arthropod Identification Forms’.”

Government of Canada. “For health professionals: Lyme disease.”

Health Quality Ontario. “Clinical Guidance Document, Management of Tick Bites and Investigation of Early Localized Lyme Disease, Health Quality Ontario.”


Ministry of Health and Long-Term Care. Infectious Diseases Protocol, 2022.