Invasive Mosquitos Found in Sea to Sky Region

Study shows disease present in small sample of airborne insects

Mosquito surveillance team (l to r): Dr. Anya F. Smith, BCCDC senior scientist, graduate students Jessica Kuzyk and Crystal Han, and vector specialist Stefan Iwasawa. Photo courtesy BCCDC.​​​​

The BC Centre for Disease Control (BC CDC) announced this week that the pilot project launched in response to several pediatric encephalitis cases in the Whistler area has indeed found invasive species and evidence of California Serogroup virus among mosquitoes in the region.

In July last year, Vancouver Coastal Health (VCH) announced they were partnering with the BC Centre for Disease Control, the Líl̓wat and Squamish Nations and the University of BC to undertake a study of the mosquito population and the viruses they carry in the Sea to Sky region.

Prior to the initiation of the project, there had been four reported cases of mosquito-borne encephalitis in the region in 2024.

Each of the patients, all children, was found to have likely acquired the infection within the Sea to Sky corridor. The viruses were identified as Snowshoe Hare Virus (SSHV) and Jamestown Canyon Virus (JCV), which are both forms of California Serogroup (CSG) viruses, which are linked to encephalitis.

The study was conducted from June through August last year, when investigators collected mosquito samples from traps places throughout the Squamish, Whistler and Pemberton areas. Twenty-seven separate species were collected and identified. The 2,500 mosquitoes were divided into 171 pools (groups of the same species, found around the same time and location), and were tested for CSGv and West Nile Virus (WNv). CSGv was detected in two of the 171 mosquito pools. No WNv was detected.

Investigators from the BC CDC say the study emphasizes the importance of monitoring mosquito populations throughout BC to better understand the risks they can pose to human health.

VCH Public Medical Health officer Dr. Ceinwen Pope says that while the risk of serious illness from mosquito-borne viruses remains low in the Sea-to-Sky area, "this project highlights the importance of ongoing monitoring and taking practical steps to prevent mosquito bites, like reducing standing water near your home, using approved bug spray, and wearing light, protective clothing."

“The pilot project gave us a snapshot of what's happening with mosquitoes in one part of BC," said Stefan Iwasawa, a BCCDC vector specialist, and part of the investigative team. “With climate change causing temperatures to rise, we may see an increase in our exposure to mosquitoes."

Although there is no known vaccine to prevent CSG viruses, all four patients diagnosed in 2024 were reported to have recovered from their illnesses.

More information can be found at the Government of Canada Health site HERE.

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