Cases of Lyme disease have now increased by more than 1,000% in a decade, as climate change pushes the limits of an array of pathogens and risk factors northward.
Populations of exotic mosquito species that can carry diseases such as dengue and yellow fever have become established in parts of Ontario, researchers say. Scientists also fear that climate change will increase the risks of microbial diseases associated with food contamination and hot weather.
Fifteen years ago, Justin Wood, a student in Ontario, started feeling sick. He said it “took about four or five years to get a diagnosis.”
When he arrived, the diagnosis was rare: Lyme disease. At the time, the tick-borne disease was responsible for only a few hundred infections per year in Canada, according to government statistics.
Mr. Wood’s experience has at least one positive point. That set him on a career path, and today he runs a private lab in Ontario called Geneticks, dedicated to testing ticks for disease.
He said his work allows him to meet many people who are “severely, severely disabled” because of Lyme disease. “It is very, very serious and the symptoms can be very, very diverse, but very, very debilitating. »
Health Canada says symptoms range from rashes and headaches to severe joint pain and memory loss. In rare cases, it can lead to death from heart infection.
Mr Wood said the number of detections of Borrelia burgdorferithe bacteria that causes Lyme disease, had recently been increasing in his lab by about 0.5% to 1% per year.
It may not seem like much, but the range of blacklegged ticks carrying the bacteria is expanding; they become more active and live longer, he said.
“This means that more and more ticks are being born every year and the number of ticks in Canada will continue to increase,” Wood said.
He said between 50 million and 175 million ticks arrive in Canada each spring on migratory songbirds.
“So you kind of add it all up, and you have more ticks, you have ticks in new places, you have more ticks carrying dangerous bacteria, and it becomes sort of a growing problem every year,” he said. detailed Mr. Wood.
Surveillance data supports this. A federal report says there were 3,147 reported cases of Lyme disease in Canada in 2021, up from 266 in 2011.
Climatic changes
” This [augmentation] “occurred in part due to climate change, which has contributed to an increase in the abundance and geographic distribution of blacklegged tick populations in central and eastern Canada,” the report states. adding that approximately 1% of Lyme disease cases in Canada were contracted abroad.
Canada’s weather conditions have already served as a barrier against many warm-weather illnesses, such as dengue fever, Zika virus, malaria and yellow fever, all of which are carried by certain species of mosquitoes.
But conditions are changing, said Victoria Ng, senior scientific evaluator at the Public Health Agency of Canada.
“With climate change, the weather will be wetter, with more extreme weather events, which could be extreme rainfall, and mosquitoes need water to be able to survive,” Ms Ng said.
Ms. Ng noted that in Windsor, Ontario, there is now a “small number” population ofAedes albopictusknown as the tiger mosquito, native to tropical and subtropical regions of Asia.
Ontario Public Health announced the detection of the first breeding population ofAedes albopictus in the fall of 2016 in Windsor. Another exotic species, Aedes aegyptinative to Africa, was also detected for the first time.
“These mosquito species are aggressive biters of humans and potential vectors of dengue, chikungunya, yellow fever and Zika viruses in warmer regions of the world,” the agency said.
At the time, the organization said it did not expect either species to survive the Ontario winter.
However, Ms Ng said scientists not only saw Aedes albopictus return all year round to the region, but they also observed them at different stages of their lives.
“We see the eggs of this particular species becoming adults, which means they have a complete life cycle and they reproduce year after year in this region of Canada,” Ms Ng said.
She said it was an example of a mosquito population, “particularly those carrying exotic viruses”, having “the potential to continue to remain established, but also to expand geographically to cause of global warming.
The concern of foodborne illnesses
Dr. Joe Vipond, an emergency physician and former president of the Canadian Association of Physicians for the Environment, said the number of cases of mosquito-borne illnesses has “slowly increased” over the past 20 years.
“What is worrying is that at some point we will be faced with diseases like dengue or malaria that could spread to Canada,” said Dr. Vipond.
He cited the example of Florida, where dengue fever did not exist in the past. But last year, the U.S. state Department of Health placed two counties under mosquito-borne disease alert after five cases of dengue fever were reported in less than a month.
It would take “radical changes” for dengue to become a concern for Canadians, he said, adding that it was not a “current concern” but “a few decades from now.” .
A 2019 article in the journal Canadian Communicable Disease Report noted that while there was no evidence of disease spreading in Canada via new populations of exotic mosquitoes, the problem required “a clinical and health response prudent public.
“While the short-term risk of incursion and establishment of exotic (mosquito-borne) diseases into Canada, facilitated or exacerbated by climate change, is very low, it is feasible. »
He said malaria was “particularly concerning” because the disease was once endemic in Canada.
A more current threat is foodborne illness associated with hot weather.
“As climate change continues and/or intensifies, it will increase the risk of negative effects on food security in Canada, ranging from an increased burden on public health to the emergence of currently unseen risks in our food chain,” said a 2019 article in the Canadian Communicable Disease Report, by scientists at the National Microbiology Laboratory in Guelph, Ontario.
He cites studies showing a “strong association” between increasing air temperatures and various infections with E. coli, salmonella and Vibrio bacteria.
“The growth, survival, abundance and diversity of pathogens will be affected by climate change throughout the food chain,” the report said.
Extreme weather events and warming oceans would also complicate the effects on the food chain and ultimately lead to more foodborne illnesses, the report said.
Lyme disease isn’t the only tick-borne pathogen that worries scientists, as climate change expands the range of carriers.
A report released by the British Columbia Center for Disease Control in 2023 indicated that two types of tick-borne parasites, Babesia odocoilei And Babesia microti, were pathogens that had recently appeared in the province. They cause babesiosis, an illness with flu-like symptoms.
“Climate change can be expected to facilitate the presence of these tick-borne diseases,” the report reads.