It's a sound Canadians know all too well: the high-pitch whine of a mosquito buzzing past your ear. Beyond annoyance and itchy bites, the emergence of clouds of these insects every spring also brings the risk of mosquito-borne diseases.
In this part of the world, two of the most common concerns are West Nile virus and eastern equine encephalitis virus. Although asymptomatic cases and minor reactions are the norm, both can cause severe neurological illness and even death.
People can protect themselves by covering their skin or using repellent, but warmer temperatures caused by climate change and more standing water from heavy rain could increase the amount of habitat and facilitate the northward migration of new species into Canada.
Carleton University PhD candidate Marc Avramov (photo by Terence Ho)
In other words, disease dynamics are changing, and keeping humans and other animals safe from potentially dangerous illnesses is an increasingly complex puzzle. Which is why Carleton University PhD candidate Marc Avramov is zooming in to develop a more detailed picture of where and when transmission occurs and, ultimately, how to mitigate this risk.
"We're trying to increase the resolution at which we track these diseases," says Avramov, a member of Carleton biologist Catherine Cullingham's Genomics of Plants, Pests and Populations research group.
"We need to identity the environments where mosquitoes are the most abundant, the locations where we see pathogens and what time of year transmission takes place. We combine all this data, do some modelling and our findings can be used to inform risk assessment and public outreach."
The Central Vector in Disease Transmission
Most mosquito-borne disease surveillance today employs a "shotgun approach," according to Avramov. Mosquitoes are trapped and tested and the results reveal where specific pathogens are present.
This type of surveillance is economically efficient but provides an incomplete picture because mosquitoes are a vector that transmit disease from one living being to another.
A mosquito bites a bird infected with West Nile virus or eastern equine encephalitis, for example, or a deer carrying eastern Jamestown Canyon virus, which can also cause neurological problems. If that mosquito bites a human, transmission can occur. Simply knowing where diseases are present doesn't give public health authorities enough information to act upon.
"Transmission dynamics are complex because there are so many different species involved," says Avramov.
"The mosquito is central to this whole equation, but our models also incorporate information about disease hosts, including birds and mammals, and the environments where this interplay takes place. We look at all of the elements in the disease cycle."
Over the past six years, Avramov's team has been capturing mosquitoes at nearly 100 locations in the Ottawa region, from parks and conservation areas to farms and residential neighbourhoods. They collect anywhere from a few insects to 10,000 in a single trap.
There are more than 80 established mosquito species in Canada, and more than four dozen in and around Ottawa. After the species Avramov collects are identified, he freezes the sample, makes "mosquito soup" using the lab's homogenizer and studies it to determine the presence of pathogens.
This information is shared with collaborators at the Public Health Agency of Canada and Agriculture and Agri-Food Canada, who can recommend localized precautions or interventions, such as larvicide programs to reduce mosquito populations.
New Species Migrating North into Canada
Different species of mosquito carry different diseases. Two types found in the Ottawa area, Culex pipiens/restuans and Coquilletidia perturbans, are known vectors for West Nile virus and eastern equine encephalitis, among other diseases.
Another species found locally, Aedes triseriatus, is being monitored because it can carry La Crosse virus, a member of the California serogroup of viruses that's present in hosts such as chipmunks and squirrels. La Crosse symptoms in humans are typically mild but can include fever, nausea, vomiting and, in severe cases, inflammation of the brain. So far, La Crosse has been identified in New York State but not in Eastern Ontario.
"Climate change can make environments more suitable for exotic species," says Avramov.
"Species can move north from warmer regions, and if the conditions allow for it, they can establish themselves in new areas. So we're on the lookout for emerging pathogens that are creeping from the U.S. into Canada."
The risk of getting bit doesn't mean people should stay indoors, however. To Avramov, dealing with mosquitoes is "the price of admission" for spending time in nature.
