Invasive Mosquitoes Carry Brain Swelling Virus in B.C.

Invasive mosquitoes carrying a virus capable of causing brain swelling have been identified in British Columbia's Sea-to-Sky region. Health authorities began an investigation after three children were diagnosed with encephalitis in August 2024. Researchers found two species of mosquitoes testing positive for California serogroup viruses, which can lead to encephalitis and meningitis.

One of the identified mosquito species, the northern house mosquito, is not native to the area. Although the virus levels detected were low, scientists emphasize the importance of understanding local mosquito populations and the viruses they carry, especially with rising global temperatures. Between 2009 and 2024, there were 15 known cases of the virus in B.C., with no cases reported in the Sea-to-Sky corridor in 2025. The overall risk of severe illness from this virus in the province is considered low.