Climate change is fuelling a spike in Lyme disease cases across Canada

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Canadians need to be more vigilant about the rapid growth in Lyme disease cases across the country, as climate change fuels an explosion of tick populations and new hot spots for infection continue to emerge from coast to coast — even in places you may not expect. 

There have been 17,080 reported cases of Lyme disease across Canada between 2009 and 2022, but while those numbers are likely an underestimate, they have grown dramatically in recent years according to data from the Public Health Agency of Canada (PHAC).

In 2009, there were just 144 reported Lyme cases in Canada — but by 2021, those numbers had shot up dramatically to 3,147. Preliminary numbers for 2022 show at least 2,168 cases.

Nick Ogden, a senior research scientist with PHAC and director of the Public Health Risk Sciences Division that conducts Lyme disease surveillance, said the single most important factor for the growth in tick populations across Canada is warmer temperatures.

"There's quite a lot of evidence to support the idea that really a major driver of the emergence of the ticks has been recent climate change," he told CBC News.

"Because of the warming climate, the new geographic footprint of Canada from Manitoba eastwards that's suitable for the ticks is increasing all the time."

Blacklegged ticks, the main vector for Lyme disease in Canada, travel north on migrating birds and rely on specific temperature conditions here to reproduce and survive, said Katie Clow, an assistant professor in population medicine at the Ontario Veterinary College.

"They need a period of time that is warm enough, for long enough, for them to find a host to feed on … If it's too cool, they starve out," she said, adding that for the last 30 years much of Canada didn't have suitable conditions necessary for tick populations to expand.

"But now, as the climate warms, these ticks that are constantly being introduced by birds are being introduced into places that were previously not suitable for their survival — but are now suitable." 

A new Canadian study published in Insect Science found that female ticks infected with the bacteria that causes Lyme disease, called Borrelia burgdorferi, had increased survival over winter months compared to uninfected ones — which could have implications on future population growth. 

"It was like a 20 per cent survival benefit, and that just amazed me," said Shelley Adamo, a psychology and neuroscience professor at Dalhousie University and lead author of the study, adding that more research is needed to see if the bacteria is helping them survive.

"What we have, though, is a strong correlation. And what it does say, regardless of the mechanism, is that in the early spring when the snow is just melting — ticks are active."

Ogden, who was not involved in the study, said the concept that Borrelia burgdorferi infection could aid the tick populations in their ability to better survive the winter has been proposed in Europe as well and warrants further study in Canada and around the world.