Mosquito research helps to detect and mitigate impacts of climate change on vector-borne diseases

By Carol-Anne Villeneuve, Kayla Buhler, Emily Jenkins and Patrick Leighton

Vector-borne diseases (diseases transmitted to humans or other animals by blood-feeding insects) are of increasing significance for both human and animal health in northern Canada. The Arctic is warming at two to three times the rate of other regions around the world, and this increase in temperature provides the perfect scenario for insects to thrive and transmit diseases that they carry. Along with increasing annual temperatures, many regions of the Arctic have experienced more precipitation. This potent combination of rising temperatures and stagnant water provides the optimal habitat for mosquitoes and other biting insects. Although the Arctic experiences surges in mosquito activity every summer, many of which are annoying but harmless, more work is needed to identify the disease-causing organisms that they carry. Under the Canadian Arctic One Health Network (CAOHN), a team of scientists from the University of Saskatchewan and the University of Montreal, along with the Nunavik Research Centre (Makivvik) and communities across northern Canada, are collecting and testing mosquitoes and surveying Arctic wildlife for exposure to these diseases. This work is crucial in a warming Arctic, as the information creates a baseline that can be used in the future to measure changes in the distribution of both mosquitoes and their diseases as the climate continues to warm.

One particular group, called the California serogroup viruses, are of interest due to evidence of high levels of human exposure in Alaska and sporadic cases in people in northern Canada. People can become infected when they are bitten by a mosquito and usually experience only mild flu-like symptoms for a few days. However, for some unlucky individuals, the infection progresses to the brain causing more serious health issues. These viruses are transmitted by Aedes mosquitoes, the most common type of mosquito in the north. Along with an abundance of suitable mosquito species in tundra ecosystems, there may also be several species of native wildlife that can serve as reservoirs for these viruses. Reservoir animals amplify the viruses to high levels in their bloodstream, providing infected blood meals for lots of mosquitoes. These mosquitoes can then transmit the viruses to people and animals that they bite. Specifically, hares, rodents and caribou may be important players in transmission of these viruses in the Canadian Arctic.

Collecting samples from snap-trapped rodents to look for California serogroup viruses. ©Kayla Buhler

For the past three years, southern and northern scientists at the Nunavik Research Centre in Kuujjuaq have sampled mosquitoes using a sweep net during daily surveys carried out in the summer. Captured mosquitoes are identified using a morphological key and tested for California serogroup viruses, among other diseases. In 2019, scientists were able to confirm (for the first time ever) that California serogroup viruses were indeed present in Kuujjuaq mosquitoes. Hunter-harvested caribou from Nunavik have also tested positive for exposure to these viruses. It’s important to note that people do not get these viruses directly from harvesting or handling wildlife, only from the bite of an infected mosquito. Furthermore, infection by California serogroup viruses causes, in most cases, only mild flu-like symptoms.

There are still a lot of questions that remain unanswered. For example, how do these viruses survive in Arctic and Subarctic environments? Which mosquito species are able to transmit California Serogroup viruses, and are these species only present in Nunavik or in more northern latitudes as well? There’s still a lot of work that needs to be done to better understand the ecology of these viruses in northern Canada and the impacts that they may have on wildlife and public health. It has often been said that knowledge is power, and by better understanding the ecology of these viruses in Arctic environments, we will better equip northern residents to detect and mitigate the impacts of climate change on vector-borne diseases.