Virus Found in Invasive Mosquitoes Detected in B.C.’s Sea-to-Sky Region

Liam O'Connell

6/2/20261 min read

Health officials in British Columbia say invasive mosquitoes carrying a virus that can cause brain swelling in humans have been detected in the Sea-to-Sky region north of Vancouver.

The discovery followed an investigation launched after three pediatric encephalitis cases were reported in the region in August 2024. Scientists began searching for invasive mosquito species between Squamish and Pemberton as part of that investigation.

Researchers found two mosquito species that tested positive for California serogroup virus, a group of mosquito-borne viruses that can cause encephalitis and meningitis in humans.

Invasive Mosquito Species Found

Among the mosquitoes detected with the virus was the northern house mosquito, a species native to Africa, Asia and Europe.

The findings were announced in a joint statement from the B.C. Centre for Disease Control, Vancouver Coastal Health, the University of British Columbia and the Provincial Health Services Authority.

According to the statement, the levels of virus detected in the mosquitoes were low. As a result, researchers were unable to confirm the specific strain of California serogroup virus present in the samples.

Climate Change May Increase Mosquito Exposure

Health officials say the study may help guide responses to future infections and improve understanding of mosquito-borne disease risks in British Columbia.

Stefan Iwasawa with the B.C. Centre for Disease Control said rising temperatures linked to climate change could increase human exposure to mosquitoes over time.

A clearer understanding of the mosquito species present in B.C., and the viruses some of them may carry, will help shape preparedness, prevention and response efforts related to California serogroup virus infections, he said.

Officials Say Serious Illness Risk Remains Low

The statement says there were 15 known cases of California serogroup virus in B.C. between 2009 and 2024.

Officials also said there have been no known cases in the Sea-to-Sky corridor in 2025.

While the detection has prompted further research and monitoring, health officials say the overall risk of serious illness from California serogroup virus in B.C. remains low.

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