Medical disclaimer: This article provides general public health information about Lyme disease risk in Ontario. Always consult a licensed healthcare provider for medical advice, diagnosis, and treatment. Part of our Ultimate Tick Control Guide for Ontario Homeowners.
Lyme Disease in Ontario: A Growing Concern
Lyme disease has become one of the fastest-growing infectious diseases in Canada. The Public Health Agency of Canada reported significant increases in confirmed cases over the past decade, driven primarily by the northward expansion of the blacklegged tick (Ixodes scapularis) as Ontario's winters warm. Cases have been confirmed in every GTA municipality, and the geographic risk zone expands each year.
Ontario Public Health now classifies much of Southern Ontario — including Mississauga, Hamilton, Oakville, Toronto, and Brampton — as areas with established blacklegged tick populations and ongoing Lyme disease risk.
How Lyme Disease Is Transmitted
Lyme disease is caused by the bacterium Borrelia burgdorferi, which is carried by blacklegged ticks. The tick acquires the bacterium by feeding on infected rodents (primarily white-footed mice) in its larval or nymph stages. When that infected tick later feeds on a human, it can transmit the pathogen through its saliva.
Key facts about transmission:
- Not all blacklegged ticks carry Lyme disease — infection rates in Ontario tick populations vary by location and year
- Transmission generally requires the tick to be attached for at least 24–36 hours
- Nymphs (tiny, poppy-seed–sized) are responsible for most human Lyme disease cases because they are hard to see and often feed unnoticed
- You cannot get Lyme disease from another person, from pets directly, or from the environment
Ontario Lyme Disease Risk Areas
The highest-risk areas in Southern Ontario for Lyme disease exposure are regions with established blacklegged tick populations:
- Mississauga / Peel Region: Confirmed blacklegged tick populations in Credit Valley, Rattray Marsh, and adjacent Conservation Areas. See: Mississauga tick control
- Hamilton: Dundas Valley, Cootes Paradise, and escarpment areas are high-risk zones. See: Hamilton tick control
- Toronto: Don Valley, High Park, and ravine corridors confirmed. See: Toronto tick control
- Oakville / Burlington: Bronte Creek, RBG, Escarpment trails. See: Oakville and Burlington tick control
Prevention Strategies: Your Layers of Defense
Layer 1: Reduce Ticks in Your Yard
Professional tick barrier spray reduces tick populations in the highest-risk zones of your property by up to 90%. Combined with habitat modification (leaf removal, lawn maintenance, wood-edge barriers), this is the most effective way to reduce your family's tick exposure at home.
Layer 2: Personal Protection
- Wear light-coloured clothing so ticks are easier to spot
- Tuck pants into socks when in long grass or wooded areas
- Apply DEET or icaridin repellent to skin and clothing
- Use permethrin-treated clothing for frequent outdoor activities
Layer 3: Tick Checks
After being outdoors, do a thorough tick check of yourself, children, and pets. Check:
- Scalp and hairline
- Behind ears
- Armpits and groin
- Behind knees
- Between toes
Shower within 2 hours of coming indoors — this helps find ticks and may wash off unattached ones.
Layer 4: Prompt Removal
If you find a tick attached, remove it promptly with fine-tipped tweezers. See: How to Remove a Tick Safely
Frequently Asked Questions
What are the symptoms of Lyme disease?
Early Lyme disease (3–30 days after tick bite) symptoms include a characteristic expanding bull's-eye rash (erythema migrans) at the bite site, fever, chills, headache, fatigue, muscle and joint aches. Not everyone develops the rash. If you've had a tick bite and develop these symptoms, see a doctor promptly. Early treatment with antibiotics is highly effective.
How long does a tick need to be attached to transmit Lyme disease?
Research indicates that a blacklegged tick generally needs to be attached for 24–36 hours to transmit the Lyme disease bacterium (Borrelia burgdorferi). This is why prompt tick removal is so important — finding and removing ticks within 24 hours of attachment significantly reduces transmission risk.
Is Lyme disease treatable?
Yes. Lyme disease caught in the early stage (localized infection) is very effectively treated with a course of antibiotics (typically doxycycline or amoxicillin). Early treatment prevents progression to more serious stages. Disseminated or late-stage Lyme disease is more complex to treat, reinforcing the importance of early detection and prevention.