Risk of tick-borne Lyme disease growing in Montreal: scientists

Confirmed cases of Lyme Disease dropped in Quebec in 2020, but experts expect the tick-borne disease to resume its steady climb this summer.

The Montreal Gazette 7 minute read June 11, 2021

Reported cases of Lyme disease have been on a steady rise since ticks carrying the bacterium that causes the disease became established here back in 2008. Dr. Catherine Bouchard, a veterinary epidemiologist with the Public Health Agency of Canada's National Microbiology Laboratory in St-Hyacinthe, looks for ticks in the woods behind her home. Dave Sidaway / Montreal Gazette

With the cold, the curfew and, hopefully, those months of COVID-19 confinement finally behind us, Quebecers are looking forward to a carefree summer in the great outdoors.

Campgrounds and cottages are booked solid, and kids’ camps are getting ready to open. Since travel abroad is still restricted, we’ve been encouraged to discover the natural beauty of our own region. Walking in nature is good for us, we’re told, and the risk of transmitting the coronavirus is much lower outdoors.

But just when you thought it was safe to head to your local nature park, public health authorities warn of a rising risk of contracting Lyme disease from the bite of an infected Ixodes scapularis, also known as a deer tick or black-legged tick.

Thanks in part to climate change, the zone where these ticks can thrive has been shifting ever northward, and Montreal Island will not be spared.

“Basically, we’re at the leading edge of a range expansion for the black-legged tick that is the main vector of Lyme disease,” said Dr. Patrick Leighton, professor of epidemiology in the faculty of Veterinary Medicine at Université de Montréal.

“What we have seen over the last 10 or 15 years is a gradual push north of the areas where this tick has been observed to be established, which we consider to mean that there are reproducing populations in an area.”

Leighton has been monitoring tick populations in southern Quebec and across Canada for the past decade. In collaboration with Quebec’s public health institute and other researchers across Canada, he tries to predict where tick populations will become established.

“Back in 2010, only about 18 per cent of people in southern Quebec … were living in zones where … there was probably an established tick population. By 2020, the projection was that 80 per cent would be living in those zones, because so many people live along the southern border.”

He said recent data bear out those predictions.

“As ticks become more established, all of Montreal is going to be in areas where, maybe not in your own backyard but maybe in a nearby park … there is a significant risk of encountering a tick. And within about five years of a tick population being established, you start to get increasing prevalence of the bacterium and Lyme disease as well”.

Lyme disease, though easily avoided with a little awareness and effort, can be a significant, even life-altering, illness. If not detected and treated quickly, the bacteria that causes it, Borrelia burgdorferi, can spread in the blood, causing facial paralysis, numbness, pain and swelling.

According to Quebec’s public health institute, the INSPQ, there were 273 confirmed cases of Lyme disease in Quebec in 2020. (Since Lyme disease is difficult to diagnose, experts believe its prevalence is underestimated.) Cases are actually down from 2019, when there were 500, but over the years the trend is clearly upward. What’s more, 247 of those 273 cases — over 90 per cent — were probably acquired here in Quebec, up from only 53 per cent of the 125 cases reported back in 2014.

The INSPQ will be updating its

Lyme disease “risk map” this month

with the latest data, collected in 2020. The map indicates three levels of risk: possible (white), present (yellow) and significant (orange). Most of the province is currently white, since it is technically possible to contract Lyme disease almost anywhere in Quebec since migratory birds can transport and drop them. But wherever white-tailed deer and white-footed mice are plentiful, infected deer ticks are sure to be thriving.

Thus, the Eastern Townships and the Montérégie regions form a sea of orange, right down to the U.S. border, and it’s only a matter of time until some forested parts of Montreal — currently yellow — turn orange, too.

The risk map combines information from three sources to stay on top of the situation. These include doctors’ declarations of diagnosed Lyme disease cases, ticks that doctors receive from their patients and send to Quebec’s public health laboratory for analysis, and active surveillance by researchers doing on-the-ground tick counts.

“You can see very clearly if you look at the map that there is this risk zone, this triangle in southern Quebec that is pushing up towards the island of Montreal,” said Leighton. “And we are starting to see evidence even north of the St. Lawrence, up in the southern Laurentians, and Lanaudière, and southwest Ottawa is another risk area.”

Last year, the Canadian Lyme Disease Research Network (CLyDRN) published a report on the results of the first year of an ongoing, cross-Canada tick surveillance project, called the Canadian Lyme Sentinel Network (CaLSeN).

The ticks are collected by researchers who drag a one-metre square piece of white flannel cloth over 2,000 square meters of ground vegetation, stopping every 25 meters to collect any ticks that cling to the passing cloth.


The Montreal region had the second highest mean tick density of the 14 Canadian regions included in the study. Of the ticks collected in the Montreal region, more than 20 per cent were infected with Borrelia burgdorferi.

“It’s safe to say that Montreal is an emerging risk zone,” Leighton said, noting that the risk is by no means uniform across the island. Although some ticks have been found in Mount Royal park, for example, it is unlikely to be a place where ticks will become well-established, because of the lack of white-tailed deer.

Ticks pass through three stages of development — larva, nymph and adult — and at each stage, they need to feed on blood in order to reach the next one. The larvae tend to feed on small mammals, such as mice. The white-footed mouse is the most common source of the bacteria that causes Lyme disease.

Infected or not, nymphs and adults crawl up plants and wait, in hopes of latching on to a passing deer, or other large mammal. (The ticks don’t hop or fly, so if you stay on trails and out of tall grass and bushes while in nature, there is less chance of snagging one.) Deer, in particular, provide an ideal environment for ticks to breed.

Tick bites are usually painless and often go unnoticed. But if the bites are infected and the patient not treated with antibiotics quickly, the bacteria that causes Lyme disease can spread in the blood. The most common symptom is a skin rash that is not painful or itchy that appears at the site of the bite. The rash may be circular, remains for at least 48 hours and expands rapidly. Some people get fatigue, fever and muscle aches. If not treated, they may also experience expanding rashes, facial paralysis, numbness in a limb, neck pain and severe headaches, swelling in the joints, chest pain, palpitations or dizziness.

Even if you get bitten and the tick turns out to be infected, you can avoid infection by removing the tick promptly. Transmitting the bacteria takes time, explained Dr. Catherine Bouchard, a veterinary epidemiologist with the Public Health Agency of Canada’s National Microbiology Laboratory in St. Hyacinthe.

“The bacteria is in the abdomen of the tick, and it takes about 24 hours to migrate back to the saliva of the tick. As the tick feeds, blood goes down to the abdomen, mixes with the bacteria in the abdomen and goes back to its mouth, and that’s when it could be transmitted. At 24 hours it starts, but by 36 hours it is more likely.”


So if you can’t stick to the trails and you don’t want to wear long pants tucked into socks, at the very least, do a tick check upon return from a nature walk by removing clothes (wash and dry them) and examining the skin.

“I was bitten thousands of times looking for ticks over the years,” said Bouchard. “It is a game changer to remove the tick by the end of the day. I have never had to take the antibiotics because I have never had any rash or other symptoms developing after a tick bite.”

If you find a tick that is attached to the skin, gently remove it with tweezers, being careful not to crush the abdomen. Preserve the tick in a clear container with a secure lid and bring it to your doctor. For more information, see the INSPQ website, inspq.qc.ca/zoonoses/maladie-de-lyme.

Roxane Pelletier, scientific adviser with the INSPQ on tick-borne diseases, says people should keep the risk of contracting Lyme disease in perspective.

“We don’t want to discourage people from doing activities outside because we know it is good for mental and physical health,” she said.

Stay on trails, and take the other precautions, she says, and if you are bitten by a tick, don’t panic.

“It’s not end of world, if you see a tick on your skin and you take it off as soon as see it, you have already limited your chances of contracting Lyme disease almost to null,” she said.



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