Last summer I was shocked when my next-door neighbor checked her kids for ticks after coming home from a park in the GTA. Do we really have ticks in the city?
We do! And Toronto has a program to count them:
"Toronto’s tick surveillance program monitors the number of blacklegged ticks, their locations and the number of them that carry the bacteria that causes Lyme disease. This information helps to determine the overall risk of Lyme disease in Toronto.The tick surveillance program consists of ticks brought in by the public and ticks found by dragging.Tick dragging is a process of collecting ticks in the environment and is done in the spring and fall when adult ticks are active." (City of Toronto Website)
The city publishes the results from each year and displays a map with combined results for 2013 to 2019. But from their website, it's hard to see how things are trending over time.
Are ticks on the rise?
Toronto Open Data has released the numbers! The data is available in csv format that would have been sufficient for this analysis, but I wanted to try out their CKAN API, which is also used by the US government (data.gov).
First I looked at the overall trend by year, plotting total black legged ticks and the number of black legged ticks that tested positive for lyme disease. It looks like the problem started in 2014, peaked in 2017, and has since plateaued.
Where are ticks on the rise?
I also wanted to understand how the number of ticks in each park is changing over time. Eighty-one parks have been surveyed, making it hard to create a visualization. Fortunately, when when I removed all of the surveillance events (Year-Park pairs) with less than five ticks, the the total count of ticks and the trend remained very similar.
I removed all surveillance events with less than five ticks without losing too much data.
Here is the data, grouped by park:
It looks like the big spike in 2017 was concentrated in Rouge Park, which is now under control.
Today, Glen Eagle Vista Trail and Upper Rouge Trail Park have ticks on the rise.
You can see my full Jupyter notebook below or on Github.