The average temperature in the Montreal region could rise by two to four degrees Celsius between 2041 and 2070, according to the most pessimistic global warming scenario. Cases of Lyme disease and West Nile virus could then increase in the metropolis. Certain species of subtropical mosquitoes could even settle in southern Quebec by the end of the century, carrying with them new zoonoses such as dengue.
This is what the Montreal Regional Public Health Directorate (DRSP) points out, among others, in its first climate portrait, entitled Assessment of the vulnerability of the Montreal agglomeration to climate changea 130-page document.
“By 2050, all regions of Quebec, with the exception of the North, should see the presence of West Nile virus increase by 10% in their mosquito population, due to climate change and temperatures that favor a habitat “improved” for vectors”, indicates to the Duty Alexandre Barris, toxicologist at the DRSP in Montreal and co-author of the report.
Five human cases of West Nile virus have been confirmed in the metropolis in 2023, according to the Department of Health and Human Services. Often asymptomatic, this infection can however cause symptoms such as fever or headache. In less than 1% of cases, it causes serious neurological damage, such as encephalitis.
In addition to this virus, the bacteria causing Lyme disease could also gain ground. Indeed, the tick that can carry it will see “its distribution area expand and its population increase” under the effect of climate warming. “If we base ourselves on projections for the middle of the century, we really expect southern Quebec to be endemic [en ce qui concerne] the tick,” says Alexandre Barris.
Seven cases of Lyme disease were reported in Montreal in 2022, according to the National Institute of Public Health of Quebec. This infection, which first appears as redness, can cause fever, fatigue and muscle pain. If left untreated, the infection could spread to the joints, heart and nervous system. In its report, Public Health emphasizes that mental health disorders can also appear in affected people, such as depression, anxiety and panic.
The threat of dengue
With climate change, the Montreal area could also “become viable for populations of mosquitoes carrying dengue”. Often asymptomatic, this disease can include fever, severe headache and, in severe cases, light bleeding and persistent vomiting. It rarely causes death.
“The problem is above all finding ourselves with outbreaks all over the island [de Montréal] because we are going to have a vector present,” says Alexandre Barris. “This vector can, for example, bite an infected person and transmit it to two people nearby. » Which risks increasing medical consultations, he adds.
According to the DRSP of Montreal, certain populations are more vulnerable to zoonoses, including children under 14 years old, who have riskier behaviors that can lead to infection (running in long grass, for example). People who are immunocompromised or have chronic illnesses are at greater risk of developing severe symptoms from West Nile virus. The same goes for seniors, due to their greater susceptibility to infections.
Montreal Public Health intends to rely on its report Assessment of the vulnerability of the Montreal agglomeration to climate change to draft a regional adaptation plan to climate change which will be presented in 2027.