Invasive mosquitoes carrying brain virus detected in B.C.

Health officials in British Columbia have detected invasive mosquitoes and a virus that can cause brain swelling in humans in the Sea-to-Sky region north of Vancouver. The discovery followed an investigation triggered by a cluster of childhood encephalitis cases in the area in August 2024. Scientists 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.

Among the mosquitoes detected with the virus were the northern house mosquito, which is native to Africa, Asia, and Europe. The detected virus levels were low, preventing researchers from confirming the specific strain of California serogroup virus. Between 2009 and 2024, there were 15 known cases of the virus in B.

C. , with no known cases in the Sea-to-Sky corridor in 2025. Health officials say the risk of serious illness in B.

C. from California serogroup virus remains low. Stefan Iwasawa with the BC Centre for Disease Control said the study informs future response efforts.

"With climate change causing temperatures to rise, we may see an increase in our exposure to mosquitoes. 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."