Residents of the Eastern Townships have known about Lyme disease for years, but now they have to watch out for another disease carried by black-legged ticks: anaplasmosis. Last summer, 35 cases of flu-like illness were reported in the Eastern Municipalities, the most of any place in Canada.
Anaplasmosis may become more common in Quebec, in part because climate change is extending tick activity periods, accelerating their life cycles, and therefore prolonging human exposure to ticks.
The upward trend caught the attention of a research team from the Faculty of Veterinary Medicine at the University of Montreal. This summer, Professors Catherine Bouchard, Cécile Aenishaenslin, Patrick Leighton and Jean-Philippe Rocheleau, together with Raphaëlle Audet-Legault, veterinarian and Master of Epidemiology at UdeM, are conducting research to determine which species of small wild mammals are reservoirs for anaplasmosis and therefore contribute to the transmission of the disease in humans.
“A tick is like a used syringe,” Bouchard explained. “Let’s say it bit a mouse for its previous meal. Suppose the bacterium responsible for anaplasmosis is circulating in the bloodstream of a mouse. Now, when the tick bites a person, it infects him with the blood of the mouse. If the mouse was a carrier of a zoonotic variant, the human would contract the disease.
Mapping distribution
With the help of the City of Bromont, the Estrie Department of Public Health and the Municipality of Broome-Missiquoi County, the team will trap rodents of various sizes (mice, chipmunks, squirrels) around Bromont during the summer to see which ones have the highest prevalence of anaplasmosis. Veterinarians will also collect ticks in the field to measure the proportion of infected ticks in the area.
Half of the sampling sites were in areas where there had been cases of human infection, and the other half where there had not been. “We want to compare the proportion of infected small mammals near human cases and further away, in addition to determining whether the spread of infection varies by species,” Audet-Legault said.
“We are interested to what extent the circulation of the bacterium is restricted,” added Bouchard. “I wouldn’t be surprised if there’s no difference between places near human cases and others.” We may find that there are more cases in humans where there is a higher population density, but the disease is equally present elsewhere. So residents will have to exercise due vigilance.”
Prevention education
In light of the explosion in human cases of anaplasmosis, efforts to promote safe behaviors among exposed populations — such as full-length clothing and routine self-examination after going outdoors — must be increased, Bouchard said.
Education efforts should be directed not only at residents but also at health care professionals who must look beyond Lyme disease when diagnosing patients from high-risk areas.
Anaplasmosis is not easily diagnosed because symptoms are usually nonspecific and mild, such as fever, chills, headache, and muscle aches. Unlike Lyme disease, a tick bite does not leave redness on the skin.
Audet-Legault also pointed out that most people infected with anaplasmosis are bitten near their homes while gardening or engaging in similar activities. “In the eastern municipalities, many people have homes on the mountainside, under crowns of mature trees. So they literally live in the tick’s habitat. We need to increase our awareness efforts as all residents are potentially at risk.
As a first step, the research team met with Bromont residents to present their research project. Interactive workshops are planned for the summer.
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