New pilot project to study mosquito population in Sea to Sky region

The project has been implemented in response to a small cluster of cases of mosquito-borne illness reported late last year. In 2024, four cases of California Serogroup (CSG) viruses — specifically Snowshoe Hare Virus (SSHV) and Jamestown Canyon Virus (JCV) — presented with encephalitis, or swelling of the brain. While these are not new infections in the province, the number and severity of the cases triggered an investigation by VCH Public Health, which found that all four patients likely acquired the infections locally within the Sea to Sky corridor. 

 “While we encourage outdoor recreation and activity, we’re advising residents and travellers to the Sea to Sky area to take preventative measures against mosquito bites, between now and fall; and if they do get bitten, to be aware of and seek health care if they develop neurological symptoms like confusion, seizures or severe headaches with fever,” said Dr. Moliehi Khaketla, Medical Health Officer for Vancouver Coastal Health. VCH Public Health has also communicated with local health professionals to ensure they are aware of the need to consider the CSG viruses as a cause for all severe neurological presentations of encephalitis and meningitis during the mosquito season. 

 “We’re also undertaking the mosquito surveillance project to learn more about the risk to the public,” said Dr. Khaketla. Mosquito traps have been set up at select sites throughout the region, guided by local community knowledge and study team expertise. The study will help update the list of mosquito species in the area and test mosquitoes for potential human pathogens. Overall, the project will gather data that helps further assess risk and inform Public Health advice on precautions against mosquito-borne illness in the Sea to Sky area. 

 JCV and SSHV have been identified provincially and nationally for decades but reported cases of human illness are rare. Cases typically occur from May to October when there is increased mosquito activity; however, this period may be extended due to the increasingly warmer temperatures associated with climate change. Prior to this cluster, 10 cases of JCV or SSHV had been reported provincially since 2009, with two in the VCH region. Serological surveys from other parts of Canada have found between one and 42 per cent of the population show evidence of prior infection, which suggests these viruses may be a cause of mild summer viral illness and an under-recognized cause of meningitis and encephalitis.

 In most cases, CSG viruses do not cause symptoms. When symptoms do occur (usually five-15 days after the mosquito bite), they are typically flu-like, including fever, headache, fatigue, and occasionally nausea or vomiting. Most individuals recover without the need for treatment, but in rare cases, the viruses can lead to more serious conditions such as meningitis or encephalitis, which may require hospitalization and a longer recovery time. Symptoms of meningitis or encephalitis may include confusion, seizures, and/or severe headaches with fever. There is currently no human vaccine available to prevent acquiring CSG viruses.

 Prevention

VCH Public Health recommends both residents and visitors to the Sea-to-Sky region take preventative measures during summer and fall. Any action that helps prevent mosquito bites or breeding can reduce the risk of infection with the CSG viruses. Simple ways to protect yourself include:

• Use mosquito repellent – Applying a mosquito repellent to areas of exposed skin is an excellent way to prevent mosquito bites. Check the product label for instructions on proper use. For more information about insect repellents, see HealthLinkBC File #96 Insect repellents and DEET.
• Wear protective clothing – Avoid dark clothing as it tends to attract mosquitoes. In areas with a lot of mosquitoes, wear full-length pants and a long-sleeved shirt.
• Install mosquito screens on windows – Consider staying indoors or in enclosed areas with screens when mosquitoes are most active or abundant, which is typically from dusk to dawn.
• Prevent mosquitoes from breeding – Anything that can hold stagnant water could be a mosquito breeding site, even small amounts. Identify and remove these areas on your property during mosquito season, this might include emptying saucers under flowerpots, changing water in birdbaths twice a week, unclogging rain gutters, draining tarps, tires and other debris where rainwater may collect, and installing a fountain to ornamental ponds or stocking them with fish. Backyard pools can also be a significant breeding ground for mosquitoes if not maintained regularly.