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.  For more information, see the health unit’s fact sheet on Lyme disease

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.

Simcoe Muskoka
Tick Surveillance
Technical Notes

Simcoe Muskoka

The following graph shows the number of Lyme disease cases among Simcoe Muskoka residents between 2000 and 2017. There have been between zero and 12 Lyme disease cases in Simcoe Muskoka every year since 2000. In 2017, 12 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 2008 and 2017, approximately one-fifth (18%) of all identified exposure locations were within Simcoe Muskoka, 24% of exposures were in an identified risk-area of Ontario, 8% were in an area of Ontario not defined as a risk area, 6% were in Canada outside of Ontario and 40% 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 2017. 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 2017, the incidence rate of Lyme disease in Simcoe Muskoka was 2.1 cases per 100,000 population and the Ontario rate was 7.2 cases per 100,000 population.


Tick Surveillance

Passive tick surveillance has been ongoing at Simcoe Muskoka District Health Unit since 2007. Between 2007 and 2017, 696 ticks were submitted to Simcoe Muskoka District Health Unit for testing. Tick submissions have increased over this time period with four ticks submitted in 2007 and 237 ticks submitted in 2017. The figure below shows that 37% of the ticks submitted to health unit between 2007 and 2017 have been identified as blacklegged ticks (Ixodes scapularis). For more information on safely removing a tick, see the health unit’s fact sheet on Lyme disease.


Of the blacklegged ticks, the majority (62%) of these ticks were acquired locally, 23% were acquired outside of Simcoe Muskoka, and 15% have an unknown acquisition. The figure below shows that five locally acquired blacklegged ticks have tested positive for the bacteria that causes Lyme disease (Borrelia burgodorferi):  one in 2012 and one in 2015 and three in 2016: three were acquired in Ontario outside of Simcoe Muskoka, one in the United States, and one had an unknown acquisition. 


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. 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.

The objective of passive tick surveillance is to understand the risk of Lyme disease infection and includes identifying locations with multiple tick submissions over multiple years. It should be noted that ticks submitted to Simcoe Muskoka District Health Unit are used to help determine areas of risk, and not for the purpose of Lyme disease diagnosis in patients.

An endemic area is defined as an area in which a reproducing population of Ixodes scapularis or Ixodes pacificus tick vectors is known to occur, which has been demonstrated by molecular methods to support transmission of B. burgdorferi at that site (source: Public Health Ontario Lyme Disease Case Definition).

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. To warrant tick drag sampling, passive surveillance indicators and suitable conditions to support populations of blacklegged ticks must be present. Passive surveillance indicators may include, but are not limited to, information about ticks submitted for identification and/or testing for the Lyme disease bacteria, assessment of exposure information from locally acquired human Lyme disease cases, and information from health care professionals. In new locations with no history of blacklegged tick populations, it would be expected that tick dragging be conducted at two different times (spring and fall) to confirm the presence of the blacklegged tick. For location of risk areas, please see the Public Health Ontario Risk map.