With parks in the United States closed due to mosquito infestations, Canadian media outlets are buzzing with concerns about the deadly Eastern Equine Encephalitis (EEE) virus carried by these insects. Yet, while this immediate threat captures headlines, the broader discussion around climate change and its role in the spread of vector-borne diseases remains largely overlooked.
Coincidentally, the Ontario Legislative Assembly is set to engage in the second reading of Bill 198 — the Ontario Climate Change Adaptation and Resilience Act, 2024 — when they reconvene in October. The legislation is a good start to protect Ontarians from extreme weather events and safeguard our agricultural systems and ecosystems; however, in its current form, the bill does not adequately address the implications of climate change on the spread of infectious diseases and lacks plans to mitigate their impact.
Among insects, mosquitoes and ticks are the most notable vectors for pathogens. Ticks are associated with Lyme disease, anaplasmosis and babesiosis, while mosquitoes serve as intermediaries for malaria, dengue, Zika, West Nile and the headline-grabbing EEE virus. Due to their unique life cycles, ticks and mosquitoes thrive only in warm weather and heavily rely on standing bodies of water to reproduce. Blessed by its geographical position, Ontario has a dry temperate climate, which has historically acted as an environmental barrier, protecting previous generations from these civilization-threatening vector-borne diseases. However, rapid climate change has eroded this safeguard, leaving Canadians vulnerable to these pathogens.
After a short winter and a long summer with record temperatures and rainfall, Ontario has become a perfect breeding ground for mosquitoes and ticks. Multiple media outlets have reported on the rise of tick-borne anaplasmosis and Lyme Disease in Ontario and across Canada. South of the border, the United States, previously protected by a similar temperate climate, has experienced a dramatic increase in incidence of mosquito-borne diseases such as Zika, yellow fever, West Nile, malaria and dengue.
A similar epidemiological change could happen in Canada: as the temperature and humidity of southern regions increase, so does the risk of these vector-borne diseases. New mosquito species from the Aedes and Anopheles genera could migrate to Canada and establish local human-to-human transmission of yellow fever, dengue and malaria. Another possible scenario involves a warming climate with more standing water, leading to an increase in the population of established mosquito species from the Culiseta and Culex genera, which could heighten the risk of transmission of endemic but rare pathogens such as West Nile virus and EEE virus.
In its current version, Bill 198 is a good start in reducing Ontarians' vulnerability to climate change, but there are gaps that members of the provincial government should consider during the second reading and in committee. I recommend that the scope of the legislation be expanded to also address the proliferation of infectious diseases facilitated by climate change. Specifically, to limit the transmission of vector-borne pathogens, Bill 198 should include measures aimed at controlling the reproduction of pathogen-carrying mosquitoes and ticks: roads should be maintained to eliminate puddles, the population of native insect-specific predators should be preserved or enhanced and habitats and animal reservoirs of the pathogens should be monitored, with plans for selective insecticide spraying to address outbreaks if necessary.
Beyond vector-borne diseases, attention should also be given to other aspects of infectious diseases amplified by climate change, such as zoonoses, fungal infections and waterborne diseases.
For instance, changes in climate patterns have impacted the migration of many avian species, which could facilitate the spread of zoonotic diseases such as avian influenza. Additionally, higher rainfall enhances the growth of many fungal pathogens, and a warming climate has led to the development of thermotolerant species, such as Candida auris and Sporothrix brasiliensis, that can more effectively infect humans. Besides creating an ideal environment for fungal proliferation, excessive rainfall and flooding can cause the contamination of drinking water with seawater or wastewater containing pathogens such as Campylobacter, Vibrio cholerae and Escherichia coli, which can lead to an outbreak of diarrheal diseases.
Our population is vulnerable to a wide range of infectious diseases whose incidence will likely increase in the coming decades due to climate change. The current concern over a single fatal case of Eastern Equine Encephalitis (EEE) virus infection is merely a glimpse of a much more terrifying future if no safeguard measures are implemented. I strongly urge the honorable members of the Ontario Legislative Assembly to collaborate with public health and “One Health” experts to expand the scope of Bill 198.
Dat Nguyen is engaged in SARS-CoV-2 and cancer research at the University Health Network in Toronto, Ont. He holds a master of science degree in virology and immunology from Johns Hopkins School of Public Health, as well as two bachelor degrees in public health and infectious disease biology from the University of California, Berkeley.
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