Tick-borne Rocky Mountain spotted fever spreading in Canada
Potentially deadly disease already found in Ontario and Quebec this year
Quebec has reported a case of the potentially deadly tick-borne disease Rocky Mountain spotted fever that was likely acquired in Ontario or Quebec. The disease was also reported in dogs in Ontario earlier this year.
Here's what you need to know about preventing, identifying and treating the disease.
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What is Rocky Mountain spotted fever?
Rocky Mountain spotted fever is a disease caused by the bacteria Rickettsia ricketssii. It's named for the fact that it was first identified in Rocky Mountain valleys of Idaho and Montana in the 1890s.
Symptoms in humans can include fever, headache, nausea or vomiting, stomach pain, muscle pain and lack of appetite.
The disease is named for the red rash that develops two to four days after the fever begins. The rash can range from pinpoint dots to red splotches.
The disease can be treated with the common antibiotic doxycycline, and most people make a full recovery.
But it can be deadly in five to 10 per cent of cases in the U.S. even with treatment, reports the U.S.-based Cleveland Clinic. Without treatment, one in four people die of the disease.
Dogs can also get Rocky Mountain spotted fever.
Dr. Scott Weese, director of the Centre for Public Health and Zoonoses at the University of Guelph, said symptoms in dogs include fever, malaise, enlarged lymph nodes, loss of appetite and muscle aches that make the animals reluctant to move. The rash can sometimes be seen inside the dog's mouth.
Dr. Alex Carignan posted this photo of the rash from a patient with Quebec's first reported case of Rocky Mountain spotted fever on social media this week. (Dr. Alex Carignan/X)
As with humans, the disease can be deadly in dogs, and Weese said one of the first dogs identified with the disease in Ontario died of it.
How is it transmitted?
It can't be transmitted from person to person. It's only acquired from tick bites — typically the American dog tick (Demacentor variabilis), which is found from eastern Alberta to Nova Scotia, especially in the southern parts of those provinces.
Weese says despite its name, it doesn't target dogs specifically, but a variety of large mammals, including humans.
Previously, people didn't worry about American dog ticks because they didn't carry Lyme disease, which people get from the blacklegged or deer tick.
"Now we're having to change our tune a little bit, realizing that this tick might not be as benign as we thought around here," Weese said.
Like black-legged ticks, American dog ticks are found in grassy and wooded areas.
Ticks can also hitch-hike between dogs or from dogs to humans — something Weese thinks happened to him the other day with his own dog at home.
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Other ticks that can carry Rocky Mountain spotted fever include the Rocky Mountain wood tick (Dermacentor andersoni) and the brown dog tick (Rhicephalus sanguineus).
Where is the disease found?
The U.S. sees 6,000 cases per year, especially in North Carolina, Tennessee, Missouri, Arkansas and Oklahoma, the Cleveland Clinic reports.
In Canada, the disease was known but rare in B.C., with an incidence of one case per 500,000 people in 2019.
There have been occasional cases of Rocky Mountain spotted fever reported in other parts of the country. A 73-year-old woman was diagnosed with the disease in 2023 after travelling from Saskatchewan to Ontario, and being in contact with her son's two dogs in Ottawa.
The Ottawa doctors who saw the case said the disease's expansion north into areas where it hadn't been seen before was likely linked to milder winters and hotter, drier summers linked to climate change, which allow ticks to expand their range.
Earlier this year, a cluster of cases in dogs was linked to Long Point Provincial Park on Lake Erie in Ontario. Weese said such a large group in a small area was a surprise. "That would suggest that this is quite well-established, at least in some areas."
This week, Dr. Alex Carignan, a microbiologist and infectious disease specialist with the regional health authority in Estrie, Que., reported a "recent" case in the province's Eastern Townships.
In an update Wednesday, he wrote that the further investigation showed that the infected patient had recently spent time both in the region of Ontario where the dogs were infected and in an area of the Eastern Townships with a lot of ticks. That makes it uncertain where the patient picked up the infection. Carignan wrote that it remains important to keep an eye out for the disease in Quebec and for local health professionals to be able to recognize it.
Dr. Isaac Bogoch, an infectious disease specialist based at Toronto General Hospital, said the Ontario dog infections and the detection of Rickettsia bacteria in ticks north of the border had shown that the disease was already in Canada.
"The real question is how much of it is here and what's the geographic distribution."
He added that other tick-borne diseases such as Lyme disease, anaplasmosis and babesiosis have spread more widely over recent years as shorter, warmer winters allow tick populations to push north.
What should people do to protect themselves and their pets?
Both Bogoch and Weese recommend people take precautions to avoid being bitten by ticks.
This can include staying on trails and away from places such as long grass and leaf litter; wearing long sleeves, long pants and insect repellent when possible while in areas where ticks might be; checking for ticks on themselves and their dogs after visiting such areas; and removing ticks promptly if found.
Weese said people with dogs are at higher risk because they're more likely to walk in areas with higher risk of tick exposure and because dogs can sometimes bring ticks into homes in their fur.
Giving dogs oral or topical tick preventive medications can greatly reduce the risk of exposure, Weese said. However, it doesn't replace other measures, and may not be as effective with Rocky Mountain spotted fever as it is with Lyme disease, since the former is transmitted more quickly.
Bogoch said health-care workers should be aware there are tick-transmitted diseases beyond Lyme that they should look out for, so that suspected cases of Rocky Mountain spotted fever can be treated immediately.
Weese recommended that if people or their pets fall ill after visiting wooded or grassy areas that might have ticks or Rocky Mountain spotted fever, they should mention the possible exposure to their doctor or vet to ensure prompt diagnosis and treatment.
He also noted that while people should be aware of these diseases, they're still rare in Canada.
"Canada hasn't been the hot spot for any of these ticks or their diseases in the past, and they won't be the hot spot compared to the U.S. But we're a hotter spot than we were."
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This article, written by Emily Chung, was originally published for CBC News on Aug. 20, 2025.