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. 62.5 percent of black-legged ticks (BLTs, formerly known as deer ticks) collected via active surveillance during the 2021 season (as of August 13) have tested positive for the Lyme disease bacteria, Borrelia burgdorferi. This is an increase over previous years where approximately 10 percent of BLTs tested positive.

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

A characteristic erythema migrans (EM) or “bull’s eye” rash is present in about 70% of cases at the site of a recent tick bite. Other symptoms include fever, malaise, headache, myalgia, neck stiffness, fatigue, 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.

Early disseminated disease

Multiple EM 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); and

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); 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. 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.

Testing Information & Requisition


Treatment & 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, including a post-exposure prophylaxis algorithm.


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, 2022  Lyme Disease Chapter. Appendix 1 (2022)


Additional Resources

1.  Public Health Ontario. "Technical Report: update on lyme disease prevention and control. 2nd edition."

2. PHAC. CCDR Report May 29, 2014, "Clinical aspects of Lyme disease."

Last Updated: 15/03/2023