Map of Simcoe Muskoka

Infectious Diseases

Lyme Disease

Lyme disease is a disease caused by the bacteria Borrelia burgdorferi. It is spread to humans through the bite of an infected tick. The only type of tick in Ontario that is capable of consistently transmitting Lyme disease is a blacklegged tick called Ixodes scapularis (formerly known as the deer tick). This tick can be found in multiple regions of Ontario, including Simcoe Muskoka.

Prior to the COVID-19 pandemic, the health unit accepted ticks from members of the public for testing by the National Microbiology Laboratory. Results of these submitted ticks can be found on our passive tick surveillance page. Currently, SMDHU is not accepting tick submissions for identification and testing. Instead, the public is encouraged to use to identify any ticks found. Data collected by eTick through digital submissions, in addition to tick dragging done by SMDHU, will continue to support SMDHU’s surveillance of local tick populations.

Lyme disease can have serious effects in humans. Early symptoms include fever, headache, muscle and joint pains, fatigue and a skin rash, especially one that looks like a red bull's eye (called erythema migrans). Lyme disease is treatable; however, if the infection is not treated in its early stages, symptoms involving the heart, nervous system or joints can occur. For more information, see the health unit’s fact sheet on Lyme disease.

Simcoe Muskoka
Technical Notes

Simcoe Muskoka

The following graph shows the number of Lyme disease cases among Simcoe Muskoka residents between 2000 and 2021. There have been between zero and 16 Lyme disease cases in Simcoe Muskoka every year since 2000. In 2021, 16 cases of Lyme disease were reported in Simcoe Muskoka.


It is often difficult to determine where persons diagnosed with Lyme disease acquired the disease because of the delay (from 3 days up to 1 month) between being bitten and showing symptoms, and the potential for multiple exposure locations. The figure below shows that between 2012 and 2021, over one-third (36%) of all identified exposure locations were within Simcoe County or the District of Muskoka, 26% of exposures were in an identified risk-area of Ontario (outside of Simcoe Muskoka), 11% were in an area of Ontario not defined as a risk area, 4% were in Canada outside of Ontario and 23% were outside of Canada (mostly the eastern United States, where Lyme disease is relatively common).



The following graph shows the incidence rate of Lyme disease in Simcoe Muskoka and Ontario between 2000 and 2021. There has been an increase in Lyme disease cases in recent years in Ontario. This may be caused by a changing climate, allowing the blacklegged tick to expand its range. In 2021, the incidence rate of Lyme disease in Simcoe Muskoka was 2.6 cases per 100,000 population and the Ontario rate was 11.5 cases per 100,000 population. Provincially, the incidence of Lyme disease has increased significantly since 2016.


More detailed data for Ontario and each health unit can be found on Public Health Ontario’s interactive Infectious Disease Trends in Ontario tool.

Technical Notes

There are many factors that influence how many cases are reported to the health unit, as explained in the Technical Notes of the Infectious Diseases page. It is unclear to what extent the global COVID-19 pandemic has influenced the reporting and spread of other infectious diseases – counts and rates of disease since 2020 should be interpreted with caution.

The confirmed case definition changed in 2015 to include those with travel to a 'risk area' as well as an endemic area for Lyme disease along with clinical and/or lab evidence. There are more risk areas in Ontario than endemic areas so this change makes the case definition more sensitive and therefore may increase the number of cases.

A risk area is defined as a location where at least one blacklegged tick was found during three person-hours of drag sampling at a location, between May and October. For location of risk areas, please see the Public Health Ontario Risk map.

Page last updated August 19, 2022