What’s your family’s Lyme disease risk?

The Lyme Risk Calculator scores 6 inputs: your GTA city (we flag cities that contain or border terrain Public Health Ontario has mapped as blacklegged tick risk area — this grouping is ours, not PHO's); your yard type (wooded/leafy/open); whether you have a dog and how it is walked; whether kids play outdoors; hiking habits; tick-check behaviour; and past tick exposure history. The output is a 1-100 household-level Lyme exposure score with personalized prevention guidance. It is a relative planning tool, not a surveillance product — for the authoritative risk map covering your address, use PHO's Ontario Vector-Borne Disease Tool.

Public Health Ontario does not publish a list of "Lyme-endemic" municipalities or health units. It maps blacklegged tick risk areas as geographic areas built from field surveillance, published through the Ontario Vector-Borne Disease Tool. Those areas are drawn from where established tick populations have actually been found, so they do not follow municipal or health-unit boundaries — one city can contain both mapped risk area and areas with no identified risk — and the map is redrawn each year. The naturalized corridors most often mapped in and around the GTA include the Oak Ridges Moraine, the Rouge watershed, the Niagara Escarpment and the Hamilton-area conservation lands, but the only way to know about your own address is to check the tool. Ticks are also carried outside mapped areas every spring by deer and migratory birds, so a bite is possible anywhere in southern Ontario.

Most research and CDC guidance states blacklegged ticks need to be attached for 24-36 hours minimum to transmit the bacterium that causes Lyme disease. The bacteria need to migrate from the tick gut to its salivary glands. This is why daily tick checks after outdoor activities are the single most effective prevention behaviour: finding and removing ticks within 24 hours essentially eliminates Lyme transmission risk.

The classic early sign is erythema migrans — an expanding bullseye-pattern rash that appears 3-30 days after a tick bite (most commonly 7-14 days). About 70-80% of confirmed Lyme cases. Other early symptoms: fever, fatigue, headache, muscle aches, joint aches, swollen lymph nodes. If you see a bullseye rash or develop unexplained flu-like symptoms after known tick exposure, see a doctor promptly — early Lyme treats easily with 14-21 days of doxycycline.

Layer these, rather than picking one: daily tick checks after outdoor activities (removing a tick within 24-36 hours is the single most reliable way to stop transmission); permethrin-treated clothing for hiking; picaridin 20% on exposed skin; showering within 2 hours of outdoor exposure to wash off unattached ticks; and reducing tick habitat in your own yard by clearing leaf litter and treating the shaded perimeter with a Health Canada-registered residual acaricide. For dogs: NexGard, Bravecto, or Simparica oral tick preventatives. We are not ranking these against each other — the personal-protection steps are what CDC and Public Health Ontario emphasise, and yard treatment reduces the habitat rather than replacing tick checks.

Possibly. Dogs are tick taxis — they sweep ticks up from grass and brush, then deposit them on furniture, beds, and you when you pet them. Three immediate actions: (1) Use a tick remover or fine-tipped tweezers to remove the tick whole; (2) Save the tick and submit a photo to eTick.ca for free identification; (3) Watch the dog and yourself for symptoms for 30 days.

No. This tool provides a relative household exposure-risk score and evidence-based prevention guidance — it is educational, not diagnostic. If you have a confirmed tick bite or unexplained symptoms, contact your family doctor or local public health unit.