Invasive Mosquitoes Carrying Brain-Swelling Virus Detected in B.C. Sea-to-Sky Region

Investigation Sparked by Pediatric Cases

Health officials in British Columbia have confirmed the presence of invasive mosquitoes and a concerning virus capable of causing brain swelling in the Sea-to-Sky corridor north of Vancouver. The investigation was launched by the B.C. Centre for Disease Control (BCCDC) following a cluster of three pediatric encephalitis infections reported in the region in August 2024. Researchers concentrated their efforts between Squamish and Pemberton to identify the source of the rare infections.

California Serogroup Virus Identified

Anya F. Smith, a senior scientist with the BCCDC, stated that researchers discovered two mosquito species testing positive for the California serogroup virus. This group of pathogens is known to cause serious neurological conditions in humans, including encephalitis and meningitis. Among the carriers identified was the northern house mosquito, a species native to Africa, Asia, and Europe that has successfully established itself as an invasive species in British Columbia.

Impact of Climate Change on Disease Transmission

While the detected virus levels were low—preventing the team from confirming a specific strain—the findings are seen as a critical baseline for public health preparedness. Stefan Iwasawa of the BCCDC emphasized that rising temperatures due to climate change are expected to increase human exposure to various mosquito species. Understanding which species are present and what viruses they carry is essential for developing effective prevention and response strategies in a changing environment.

Assessing the Public Risk

Despite the detection, health authorities including Vancouver Coastal Health and the University of B.C. maintain that the current risk of serious illness remains low. Historical data shows only 15 known cases of California serogroup virus in B.C. between 2009 and 2024, with no new cases reported in the Sea-to-Sky corridor so far in 2025. Officials continue to monitor the situation while advising the public to take standard precautions against mosquito bites during the warmer months.