Health·Second Opinion

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

Canadians need to be more vigilant against the rapid growth in the number of Lyme disease cases across the country, as climate change fuels an explosion of tick populations and new hotspots for infection continue to emerge from coast to coast.

Tick populations growing rapidly, new Lyme disease hot spots emerging coast to coast

This undated photo provided by the U.S. Centers for Disease Control and Prevention (CDC) shows a blacklegged tick, which is also known as a deer tick.
This undated photo provided by the U.S. Centers for Disease Control and Prevention (CDC) shows a blacklegged tick, also known as a deer tick. There have been 17,080 reported cases of Lyme disease across Canada between 2009 and 2022. (CDC/The Associated Press)

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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." 

Ticks surviving extreme temperatures

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.

"These things have evolved together for millennia," he said. "And so the idea that one may help the other is not something that we can rule out." 

Another new study from researchers at  Washington State University, published in the journal Ecological Monographs this week, found blacklegged ticks were able to survive both extreme cold and heat in nature — challenging previous research to the contrary. 

An adult blacklegged tick.
An adult blacklegged tick. A new Canadian study found that female ticks infected with the bacteria that causes Lyme disease had increased survival over winter months compared to uninfected ticks. (Bertrand Guay/AFP/Getty Images)

More Canadians at risk of Lyme disease

The massive growth in tick populations across the country over the past decade, and the potential for ticks to pose an earlier seasonal threat due to climate change, is also putting a growing number of Canadians at risk of developing Lyme disease in the years ahead.

The first sign of Lyme disease infection can be a telltale circular red rash around the spot of a tick bite, which can later progress into symptoms like headache, fever, chills, fatigue, aching muscles and joints, swollen lymph nodes and muscle spasms or weakness.

If detected early, the treatment is a short course of antibiotics that cures the majority of people. Left untreated, it can result in much more serious symptoms like facial paralysis, meningitis, heart problems, nerve damage and inflammation of the brain and spinal cord.

The question of why some people recover from Lyme disease quickly, while others experience much more severe and long-term symptoms, is another area of study that has long been a mystery to researchers.

A new study published in the U.S. Center for Disease Control and Prevention's Emerging Infectious Diseases journal found an immune system biomarker in the blood was higher in people with chronic Lyme disease symptoms, even after they were treated with antibiotics.

That means the long-term symptoms in patients with high levels of the biomarker, called interferon-alpha, may not be due to an ongoing infection, but instead may be due to the body's immune response causing chronic inflammation — even after the infection is gone.

The study included 79 long-term Lyme disease patients and could point researchers in new directions on potential treatments, if the findings are replicated in larger studies with more participants and shown to be an effective indicator for more severe symptoms.

"There should be at least a consideration that these persistent symptoms after Lyme are driven by the immune response rather than persistent infection," said Klemen Strle, lead author and assistant professor of molecular biology and microbiology at Tufts University.

"And that's important because then the treatment of the symptoms should be refocused from longterm antibiotics to something that maybe dampens the immune response."

WATCH | New vaccine in development as Lyme disease on the rise:

New Lyme disease vaccine for humans being developed

1 year ago
Duration 1:54
A new vaccine for Lyme disease is in the works, and researchers are seeking thousands of volunteers in the U.S. and Europe to test it out.

A new vaccine for Lyme disease is currently in development in early clinical trials in the U.S., while a previous vaccine called LYMERix was discontinued in 2002 due to insufficient consumer demand, waning protection over time and reports of side effects like arthritis.

Public Health Ontario has also begun using a new type of blood test for Lyme disease this year, similar to a serological test for COVID-19, which may help better detect the presence of the disease in an infected patient.

Ticks carrying more diseases

There are also different pathogens that ticks can carry that pose a danger to human health, other than Lyme disease, which Clow said Canadian surveillance networks are already starting to detect in Eastern Ontario, Southern Manitoba and Southern Quebec.

One tick-borne disease, caused by the bacteria Anaplasma phagocytophilum, can cause anaplasmosis in humans and can lead to fever, chills, severe headaches, muscle aches, nausea, vomiting, diarrhea and in severe cases respiratory and organ failure, bleeding problems, and death.

PHAC researchers published a study last year on an "unusual" cluster of 25 cases of anaplasmosis in the Estrie region of Quebec in 2021, adding it "provides further evidence that [the pathogen] may now be established along the southern border of Quebec."

Clow said two other pathogens, like Powassan virus that can cause long-term neurological issues and Babesia microti that causes a Lyme-like disease, can also be carried by ticks and brought into Canada — and researchers are on high alert for emergence of these cases.

"This is concerning, because then we have more than one thing that we're worrying about that is being transmitted by these ticks," said Clow, adding that cases of these are low. "But we get early warning signals, and we can monitor over time to see if things are changing."

There are also different tick species emerging in Canada due to climate change and host migration that are establishing themselves in the country more and more. While many feed on wildlife hosts and don't pose a risk to human health — some do.

The lone star tick now has suitable habitat in parts of Canada due to climate change, which Clow said could introduce new pathogens into the country that could affect human and animal health, and the Asian longhorned tick is currently spreading in the U.S.

WATCH | Disease-carrying ticks in new areas of Canada:

Why are ticks spreading to cities across Canada

4 years ago
Duration 2:34
They may be incredibly small but ticks can cause some serious health issues. Cases of Lyme disease have doubled in Canada within a year. We look at the threat and tips you need to know to protect yourself.

Awareness among Canadians low

But as research into the rapid spread of tick populations across Canada continues — awareness among Canadians on how to identify ticks, prevent infections and understand where they're most at risk is limited.

Another growing area of concern among researchers is the spread of tick populations driven by climate change into new highly populated areas of the country that haven't before seen ticks encroach into them — and may not understand the risks they pose. 

"We still have plenty of areas that are suitable within highly populated areas that still haven't seen these ticks expand into them," Clow said. "We know that tick populations are going to continue to expand and it's really just sort of a matter of time because we know that the habitat and climate is suitable."

Ogden said Lyme disease hot spots are on the rise in Canada, particularly in regions like southern Quebec and Ontario, where tick populations have become widely established.

"Obviously not everywhere in that region are you at risk from Lyme disease, because the ticks need woodlands to survive in," he said. "But overall, I mean, at a kind of Canada-wide view — we're now seeing that there are whole regions, as in the U.S., where there is a risk of Lyme disease."

A 2023 national survey on tick awareness by the Canadian Veterinary Medical Association of 1,200 respondents found less than half of Canadian pet owners were familiar with any tick species, and were more concerned about Lyme disease in their dogs than themselves.

"There's still additional outreach that needs to be done with the general public … there are certain areas where we now just need to consider that if you are going out into wooded and brushy areas, that there are probably ticks there," Clow said.

"Getting into the habit of doing tick checks, staying on marked paths out of the brush and then covering up just needs to become a daily routine that we need to practice."

Canadians can take measures to prevent tick bites by wearing protective clothing, tucking pants into socks, using insect repellent and performing full body checks after spending time outdoors in wooded or grassy areas.

If you've been bitten, carefully remove the tick and save it in a container labelled with the date of the bite and take it to your doctor for testing.


Adam Miller

Senior Health Writer

Adam Miller is a senior health writer with CBC News. He's covered health and medical science news extensively in Canada for over a decade, in addition to several years reporting on crime, politics and current affairs throughout Asia.

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