Lyme Disease

Reporting Obligations

Lyme disease is reportable to the medical officer of health as per Regulation 135/18: Designation of Diseases made under the Health Protection and Promotion Act. An electronic copy of the reporting form is available for download. The form includes the definitions of a confirmed case. Confirmed cases must be reported by the next working day. Forms can be faxed to:

  • Fax: (807) 625-4822


NEW - MARCH 2023

A different testing algorithm for Lyme disease will be implemented by the Public Health Ontario Lab (PHOL) as of April 1, 2023. Please see the full memo from Dr. S. Wajid Ahmed, Associate Chief Medical Officer of Health, Public Health by clicking here.

This method provides 15-25% higher sensitivity during early-localized disease. The changes in testing algorithm will help support a clinical Lyme Disease diagnosis, particularly in the early localized stage of the disease (by reducing the chances of a false negative result) and help to improve the turnaround time for Lyme Disease testing, which can lead to earlier intervention.


Local Epidemiology

Active tick surveillance results have identified a local, reproducing population of blacklegged ticks (Ixodes scapularis) in Thunder Bay. 55% percent of black-legged ticks (BLTs, formerly known as deer ticks) collected via active surveillance during the 2022 season tested positive for the Lyme disease bacteria, Borrelia burgdorferi. This yields a 3-year average of >30% of black-legged ticks infected with Borrelia burgdorferi, which is important for the post-exposure prophylaxis decision algorithm published by Health Quality Ontario.

As of May 1, 2019, Thunder Bay and immediately surrounding areas have been designated as a risk area for Lyme disease by Public Health Ontario. See the 2022 Ontario Lyme Disease Map, for more information.


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 three stages in which infected persons may experience any of the following symptoms:

Early localized disease

Erythema migrans (EM) or “bull’s eye” rash is present in about 70% of cases at the site of a recent tick bite . EM is a pathognomonic sign of Lyme disease. It 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. Some lesions are homogeneously erythematous, whereas others have prominent central clearing or a distinctive target-like appearance. A single primary lesion must reach greater than or equal to five cm in size across its largest diameter. On the lower extremities, the lesion may be partially purpuric. It appears 1–2 weeks (range 3–30 days) after infection and persists for up to 8 weeks.

Other symptoms include fever, malaise, headache, myalgia, neck stiffness, fatigue, lymphadenopathy and arthralgia.

Early disseminated disease

Multiple EM in approximately 15% of people occurs several weeks after infective tick bite, cranial nerve palsies, lymphocytic meningitis, radiculitis, 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. behaviour changes, sleep disturbance, headaches), conditions such as conjunctivitis, optic neuritis, keratitis, and uveitis 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 exposure to geographic areas where blacklegged ticks are common (see the Ontario Lyme Disease Risk Areas Map) including those in occupations/activities in tall grass or wooded areas where ticks reside.

For a map of Canadian risk areas outside of Ontario, visit the Government of Canada’s “Risk of Lyme Disease to Canadians” website.

Minnesota and Wisconsin are considered “high prevalence” areas for Lyme disease. See the CDC’s “Lyme Disease Maps: Most Recent Year” website.


Diagnosis & Laboratory Testing

Diagnosis is based on clinical and epidemiological findings.

Serological evidence using a modified two tier testing (MTTT) to support clinical diagnosis of early and disseminated Lyme Disease. For more information on this updated testing, see a March, 2023 memo from Dr. S. Wajid Ahmed, Associate Chief Medical Officer of Health, Public Health.

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.

Testing Information & Requisition


Treatment & Case Management

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

Physicians and Nurse Practitioners

See the Clinical Guidance Document, Management of Tick Bites and Investigation of Early Localized Lyme Disease, updated in 2023. The document also includes information on laboratory testing and recommendations for treatment of patients with early localized Lyme disease, including a post-exposure prophylaxis algorithm.

More in-depth guidance for all stages of Lyme disease can be found in the clinical practice guidelines by the Infectious Diseases Society of America.


As of January 1, 2023, pharmacists can prescribe post-exposure prophylaxis.  See the Assessment and Prescribing Algorithm for Pharmacists: Antibiotic Prophylaxis to Prevent Lyme Disease following a Tick Bite, released in 2023.


Patient Information

Patient Fact Sheet

Additional TBDHU-produced patient education resources are available to download:



1. Ministry of Health and Long Term Care, Infectious Diseases Protocol - Appendix 1 (2022) Lyme Disease.

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