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The Public Health Agency of Canada (PHAC) has confirmed a case of hantavirus in a cruise passenger currently isolating in British Columbia following laboratory testing.

Experts share their thoughts on how climate change affects Canada's insect population.

In Canada, vector-borne diseases have always been a problem, but in recent years this problem has been exacerbated due to climate change. These insects (or “vectors”) need warmer weather to thrive and with climate change affecting so much of our way of life, we need to anticipate how these diseases will shape our future. 

Dr. Victoria Ng, a senior scientist and epidemiologist at the Public Health Agency of Canada (PHAC), specializes in mosquito-borne diseases, particularly those seen across Canada.

In Windsor, she will be starting a new program in collaboration with the University of Windsor Let’s Talk Science using Let’s Talk Science volunteers, mainly students from the University of Windsor. The program is currently PHAC-led, and still undergoing some developments, but it will essentially give children between grades five and eight the opportunity to build insect traps that will be used to capture mosquitoes that will then be sent back to PHAC for testing. A presentation aspect will also be used to educate the children on mosquito-borne diseases and how to prevent yourself from getting sick. 

“We’re having meetings [now] to talk about the logistics, like the presentation that we’re giving to schools,” Ng says. “We’re doing pre-tests of the presentations at the meetings and talking about the logistics of how we get those samples from the kids to the schools, from the schools to the universities, from the universities to the lab.”

But trapping and studying mosquitoes isn’t entirely new. The mosquito surveillance program, launched in 2020 in Essex County in Windsor, Ont., by the Windsor-Essex County Health Unit has workers deploying mosquito traps to monitor how far certain species have spread across the county. They are specifically looking for the species that transmit diseases.

The need for these mosquito trapping programs is simple: the warming climate has made it easier for insects to reproduce in Canada and worldwide, increasing the chances of spreading vector-borne diseases. 

One of the most notorious examples of vector-borne diseases is Lyme disease, which has seen a growth of over 19,000 cases across Canada between 2009 and 2023, according to a report from the government of Canada. Caused by the bites of black-legged ticks infected with the disease, the growing cases are attributed to hotter summers and milder winters, which prolong a tick’s lifespan, allowing them to thrive and reproduce in areas they previously couldn’t. 

However, these are not the only insects that pose greater risks to people with the warming climate, and Lyme disease is not the only sickness Canadians need to worry about. Public health and infectious disease experts are working to prepare Canada for an insect invasion that is already partially underway. 

Central and eastern Canada, specifically regions where the climate is generally colder, are now experiencing warmer temperatures and more precipitation at times of the year when the region is historically cold and dry. This change allows insects like the ticks that cause Lyme disease to thrive and reproduce, but it also allows other insects like mosquitoes to do the same. With an extended lifespan due to this warmer weather, the disease pathogen inside the vector spreads to other mosquitoes in the area. According to a report from the Climate Atlas of Canada, Lyme disease and West Nile virus are the greatest threats to Canadians' health at this time because of the way these vectors can continue to survive when they should be dying off. 

For example, reported West Nile virus cases have been spotty over the years, experiencing large growths in 2020 with 166 cases, but dropping back down to 45 cases in 2021. A 2022 map of Lyme disease risk areas also highlights the growing presence of the disease in southern Ontario, Quebec, Manitoba, Alberta, British Columbia, and most areas of New Brunswick. 

Ng explains how she notices a pattern of warmer weather speeding up the development of vectors like mosquitos, in turn causing the disease pathogens they carry to spread faster.

“But the environment and climate is just one part of the ecosystem,” she says. “I don’t think we can say climate change is the only cause of the expansion of potential vectors and potential increases in human diseases. It’s all very complex and intertwined, but I think climate is one key factor.” 

She lists increased travel and increased urbanization as other potential factors of mosquitoes’ growing presence across Canada, noting that while there is no one answer for why vector-borne diseases are seeing a growth in the population, there are likely causes. Other experts share similar opinions.

Dr. Heather Coatsworth, a chief research scientist of field studies at PHAC, spends her time in the National Microbiology Lab working on studying vector-borne and zoonotic diseases. She mentions the surveillance wing, where scientists study mosquitoes and ticks, examining them for pathogens that can cause human disease. She is also intimately familiar with the history of some of these vector-borne diseases and how they began trickling into Canada.

“With the increase in warmer weather, as well as other things like humidity and us getting a lot closer to animals in a lot of places, so increased urbanization has really driven the presence of the bacteria in a lot of other places to the point of endemicity, both here where I am in central Canada, as well as in eastern Canada,” she says. “And we’re seeing cases pop up slowly in western Canada as well.” 

Coatsworth also cautions that we can expect to see other tick-borne variants of diseases in the future. In fact, we’re seeing some right now with diseases like anaplasmosis, which also spreads through the infected bites of black-legged ticks. There has been an increase in human cases since 2014, mainly in the areas where Lyme disease cases are most prominent, due to the effects of milder winters. 

This pattern is seen with all insect vectors, as they are cold-blooded, explains scientist and University of Toronto professor Ian Crandall.

“If we have a warmer spell of weather, the mosquitoes’ biochemistry speeds up. And what that means is the time between when it hatches out of its egg to when it becomes an adult and becomes infective is slowed down,” says Crandall. “One of the effects of that is that then you get more breeding cycles, or more replication cycles in a given summer. And if that summer is long, it means you get more still.”

With the risk of vector-borne diseases increasing, experts explain ways to manage the risks with some common sense steps and mitigation strategies, both at individual and government levels. 

Coatsworth explains the simple ways to remain protected from ticks specifically, ranging from applying bug sprays to ensuring that clothing is properly covering your body. At a governmental level, certain provinces and municipalities have surveillance programs for ticks, which help them determine whether or not an area is safe for citizens to be outdoors in. Local public health messaging, like putting up signs reminding citizens to perform tick checks in outdoor areas where they could be at risk for insect bites, is also a large part of the mitigation process.

“Some municipalities will do their own mitigation techniques,” Coatsworth says. “They can put out baits in the population to deer or mice, which are similar to things you would give your dogs when they go outside as a measure to protect against ticks, to try and get the animal population to have a lower exposure to ticks as well.” 

For mosquitoes, mitigation tactics are similar. Ng talks about the difference between ensuring you are protected at the individual level and the community level. At an individual level, one can try to prevent getting bitten by mosquitoes by wearing brighter colours (mosquitoes are attracted to darker colours), or removing stagnant water from backyards, which provide a place for mosquitoes to lay their eggs. At the community level, there are programs created by PHAC that enlist citizens to collect mosquito samples that will aid scientists with ongoing research on mosquito-borne diseases, like the aforementioned mosquito surveillance program.

With Ng’s new study in Windsor, the education she and her team will be providing to elementary school children will further contribute to this research. In helping the children build these insect traps, she and the volunteers will be contributing to Let’s Talk Science’s 30-year history of helping get science programs into schools, something incredibly beneficial to these children as the risk of vector-borne diseases continues to grow.

As of now, there are resources online, mainly the government of Canada’s website, that can inform the public about how to prevent themselves from getting tick and mosquito bites, as well as helpful information about risk areas for things like Lyme disease. Having an understanding of how to remain protected from vector-borne diseases is paramount, especially as temperatures continue to rise. As they do, understanding what the future will look like is a tricky question. 

Experts know that the climate is warming and a result of that are changes to mosquito environments. Even a single degree change in their environment will cause changes in their biology and ecology, as well as how they transmit diseases to humans. Warmer temperatures, coupled with more frequent precipitation, will lead to an increase in the types of vectors that transmit diseases to humans. 

“With climate change, if in general, we see a much more warmer environment and more rainfall, we would expect that potentially we will start having the suitability for local transmission [of vector-borne diseases],” says Ng. “And so in terms of climate change, we expect to see some cases of local transmission for certain diseases, how much we don't know. But we suspect that that will happen and you only have to look to Europe or even the U.S. to see that that has happened.”

In terms of keeping the public informed of measures and programs dedicated to monitoring the spread of vector-borne diseases, many resources are available online. But Coatsworth tells me that on April 1st PHAC will be speaking broadly about the spreading cases of Lyme disease in Canada to better track and monitor them. 

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