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Lyme Disease

Lyme disease is an infection caused by the bacteria Borrelia burgdorferi. These bacteria are spread by the bite of blacklegged ticks (also known as deer ticks).1

How does Lyme disease affect humans?

Lyme disease is transmitted (passed on) to humans through the bite of an infected blacklegged tick (deer tick).1 The transmission cycle (how the bacteria is passed) begins when ticks feed on birds and small mammals that carry Lyme disease. Once the tick bites an infected animal, it becomes infected with Lyme disease and could possibly transmit the bacteria to humans through a bite.

A tick can transmit infection after being attached for 24 to 36 hours, because it takes time for the bacteria to travel from the tick’s gut into its salivary glands.1 It is important to check for ticks and quickly remove them in order to prevent Lyme disease.1 If a blacklegged tick has Lyme disease but is removed right away, it is unlikely that infection will be passed on.


What are ticks?

Ticks are:

  • Closely related to spiders.
  • Very small (1 to 5 mm) when unfed, and cannot fly or jump.
  • Usually found around the edges of trails, tall grass or bushes. 

View ticks that can be found in Middlesex-London →

Do all ticks transmit Lyme disease?

No, not all ticks transmit (pass on) Lyme disease. In Ontario, Lyme disease is only transmitted through the blacklegged tick (deer tick).2

Where are blacklegged ticks found?

Blacklegged ticks (the ones that carry Lyme disease) are most often found along the shores of Lake Erie, Lake Ontario and the St. Lawrence River.1 Blacklegged ticks are known to feed on migratory birds, and as a result, they are found mainly along the routes that birds fly and can travel throughout the province.1

  • Picture of a female blacklegged tickSubmit a Tick
    The Health Unit accepts tick submissions year round. Learn how to submit ticks.
  • A picture of a family hiking in the woodsPrevention and Personal Protection
    Lyme disease can spread through the bite of infected blacklegged ticks (deer ticks). Learn how to protect your family and prevent tick bites.

Areas in Ontario that are known for Lyme disease and blacklegged ticks include:1,3

  • Point Pelee National Park
  • Rondeau Provincial Park
  • Turkey Point Provincial Park
  • Long Point peninsula, including Long Point Provincial Park and the National Wildlife Area
  • Wainfleet bog near Welland on the Niagara Peninsula
  • Prince Edward Point
  • Parts of Thousand Islands National Park

Risk areas include:3

  • Locations around Kingston
  • Along the St. Lawrence Valley to the border with Quebec and northeast towards Ottawa
  • Western Ontario in the region of Lake of the Woods
  • Pinery Park on the shore of Lake Huron
  • Rouge Valley region of eastern Toronto

View these Lyme disease risk areas on a map of Ontario.

It is important for residents to protect themselves from tick bites when spending time outdoors, especially when travelling to risk areas in Ontario, Eastern Canada and the United States where there are known populations of blacklegged ticks.

What is being done about Lyme disease in Middlesex-London?

The Middlesex-London Health Unit follows up on human Lyme disease cases. The Health Unit looks for blacklegged ticks to find out whether or not Lyme disease is in the area. The Health Unit monitors ticks by having the public submit any ticks that they find to the Health Unit, and by going out to look for ticks in wooded or grassy areas where ticks might be found. When ticks are found, they are identified in the laboratory. If a blacklegged tick is found on a human, it is sent away for testing to see if it carries Lyme disease. Learn more by reading about tick surveillance.

Additional Information

For more information on Lyme disease, visit the Government of Canada or Public Health Ontario website.

For more information on the activities carried out by the Vector-Borne Disease Team, please continue to browse this website, or call:

  • 519-663-5317 ext. 2300

For more information on Vector-Borne Diseases and human health, please continue to browse this website, or contact the Infectious Disease Control Team by calling:

  • 519-663-5317 ext. 2330


Please note: Where indicated, the source of the information on this web page is Public Health Ontario. © Queen’s Printer for Ontario, 2017, or the Government of Canda's Risk of Lyme disease to Canadians website. The information is a copy of the version available at the URL in the references section below.

Date of creation: October 1, 2012
Last modified on: May 10, 2018


1Ontario Agency for Health Protection and Promotion (Public Health Ontario). (2016, June). Technical report: Update on Lyme disease prevention and control. Second edition. Retrieved from
2Ontario Agency for Health Protection and Promotion (Public Health Ontario). (2018, April 17). Lyme disease Retrieved from
3Government of Canada. (2017, November 10). Risk of Lyme disease to Canadians Retrieved from