Lyme Disease

Lyme disease is an infection spread by the bite of an infected blacklegged tick. The bite is usually painless and the tick is small, so many people never notice it. Untreated, it can spread to the joints, nerves and sometimes the heart.

What Lyme disease is, and what it is not

Lyme disease is caused by a bacterium, Borrelia burgdorferi, carried by blacklegged ticks. It is not passed between people, and it is not a wilderness illness: most bites happen close to home, near trees, shrubs, tall grass and leaf litter.

It is also no longer rare here: the Public Health Agency of Canada reports the tick range spreading as the climate warms. The best-known sign, a bull’s eye rash, is often absent or hard to see, so no rash does not mean no Lyme disease.

Signs and symptoms

• An expanding rash at the bite site, growing beyond 5 cm, sometimes ring-shaped and hard to see on darker skin
• Fever, chills, headache, fatigue and swollen lymph nodes
• Pain that moves between joints, bones and tendons
• Arthritis with swelling in the knees, ankles, elbows or wrists
• Facial paralysis, dizziness, numbness or tingling, and trouble concentrating
• Palpitations or an irregular heartbeat

Timelines differ. Early signs usually start 3 to 30 days after a bite; joint, nerve and heart features can appear months later.

What raises the risk

Some risk factors cannot be changed:

• Living in or visiting areas where blacklegged ticks are established and spreading, including parts of Ontario, Nova Scotia, Quebec and British Columbia
• Tick activity in any month when temperatures stay above freezing, not only in summer

Others can often be worked on, usually with support from a health care team:

• Time spent in or near trees, shrubs, tall grass or leaf litter
• Repellent use, where PHAC describes products containing DEET or icaridin, and permethrin-treated clothing
• Checking yourself, children, gear and pets after being outdoors, since a tick must stay attached to infect you

How Lyme disease is diagnosed in Canada

Early Lyme disease is diagnosed clinically, from where you have been, your symptoms and an expanding rash; blood testing is not needed when that rash is present. For laboratory confirmation Canada uses two-tiered serology: a screening enzyme immunoassay, then a confirmatory test. Both look for your immune response, not the bacterium, so they can be negative in the first weeks. Later assessment may add a heart tracing or a lumbar puncture.

Treatment and day-to-day management

Lyme disease is treated with antibiotics, started promptly. Depending on the stage, a health care team may discuss:

• An antibiotic prescribed by a clinician, with choice and length depending on the stage
• Hospital assessment for Lyme carditis, which affects the heart’s electrical conduction, or infection of the brain, spinal cord or eye
• Referral to cardiology, neurology, rheumatology or infectious diseases
• Symptom management, physiotherapy and rehabilitation if fatigue or pain continue

PHAC states that prolonged antibiotic therapy has not been shown to improve symptoms or outcomes. These are decisions for you and your own clinician.

When to talk to a doctor

• Call 911 or go to an emergency department for fainting, chest pain, a very slow or irregular heartbeat, severe headache with a stiff neck, confusion, or new weakness.
• See a health care provider promptly for an expanding rash, or fever and flu-like symptoms, after being outdoors in a tick area. Say where you have been.
• See a health care provider if you find an attached tick and do not know how long it was there.
• Book an appointment for new joint swelling, facial drooping or numbness after a possible tick exposure.

Why clinical research matters for Lyme disease

Two problems drive Lyme disease research. Antibody testing is unreliable in the first weeks, which is when treatment matters most, so better direct tests are needed. PHAC also acknowledges that some people keep having fatigue, pain and trouble concentrating after antibiotics, without a settled explanation. And there is no Lyme disease vaccine available: a candidate completed a phase 3 trial with Canadian sites, and in March 2026 the sponsors reported the criterion set for its primary endpoint was not met.

Taking part is voluntary. You give informed consent first, and you can stop at any time without affecting the care you get from your own doctor. No one can say in advance whether a study will help you personally.

Learn more from Canadian sources

• Public Health Agency of Canada: Lyme disease
• Tick-borne disease surveillance in Canada
• eTick.ca tick identification
• Canadian Lyme Disease Research Network