Viruses found in mosquitoes in B.C.’s Sea to Sky region during testing

A mosquito is shown in a laboratory in Strathroy, Ont., on May 10, 2007. THE CANADIAN PRESS/Dave Chidley

A study of mosquitoes in B.C.’s Sea to Sky region revealed viruses in some species of the insect that can make people ill, Vancouver Coastal Health announced Monday.

Health officials launched the surveillance project last year after three children in the Whistler area contracted mosquito-borne California serogroup viruses (CSGv) in 2024 and suffered from encephalitis, or swelling of the brain.

“As part of a pilot project funded by the UBC Centre for Disease Control, we collected and identified mosquitoes along the Sea-to-Sky corridor, from Squamish to Pemberton, looking for invasive and endemic mosquito species,” Dr. Anya F. Smith, principal investigator for the project, said in a news release.

“Two of the mosquito species that we tested showed positive results for CSGv — a group of mosquito-borne viruses that can cause illness in people.”

Between June 16 and August 25, 2025, researchers trapped 2,575 mosquitoes at 11 different sites in the region, with 27 different species of the insect among them.

The bugs were placed in 171 “mosquito pools” of the same species found at the same time and location, and tested for CSGv and the West Nile virus.

CSGv was detected in two of the pools, Culex pipiens/restuans and Aedes cinereus. Officials say the virus levels were low, and researchers were unable to identify the specific strain in the mosquitoes. West Nile virus was not detected in any of the mosquitoes.

“The pilot project gave us a snapshot of what’s happening with mosquitoes in one part of B.C.,” said Stefan Iwasawa, a B.C. Centre for Disease Control vector specialist, in the release. “With climate change causing temperatures to rise, we may see an increase in our exposure to mosquitoes.”

When humans get infected with California serogroup viruses, they are typically asymptomatic or experience a mild flu-like illness. But in rare cases, the mosquito-born pathogens can cause encephalitis or meningitis, according to the health authority.

There were 15 known cases of CSGv in B.C. between 2009 and 2024, and zero recorded in the Sea to Sky corridor in 2025.

VCH says the risk of developing a serious illness from CGSv in B.C. is “still considered to be low.”

“Having a better understanding of the mosquito species that people living in B.C. are likely to encounter — and the viruses some of them can carry — will help inform preparedness, prevention and response efforts related to CSGv infections,” Iwasawa said.

Health officials recommend taking extra precaution against mosquitoes, especially from dusk to dawn when they are most active, by wearing long sleeves and using mosquito repellent. People are also encouraged to remove standing water around their homes.