Mosquitoes test positive for West Nile Virus

Alburgh and Vergennes mosquito pools are first to test positive in 2023 

Mosquitoes collected in Alburgh and Vergennes during the week of July 24 have tested positive for West Nile virus at the Vermont Dept. of Health Laboratory. So far this season, 824 mosquito pools — groups of up to 50 mosquitoes of the same species collected from the same site — have been tested. These are the first detections of West Nile virus in Vermont in 2023. There have been no reported human or animal cases of West Nile virus disease so far this year. The last confirmed human case was in 2021. 

Since 2002, there have been 17 human cases of West Nile virus in Vermont. There have been no human cases of the more deadly Eastern equine encephalitis (EEE) since 2012. 

West Nile virus is spread through the bite of an infected mosquito. Historically, the virus has been found in all counties of Vermont from June through October, but the risk is highest in late summer and early autumn. 

Most people who are infected do not have any symptoms. Some people will have fever, headache, body aches, joint pains, vomiting, diarrhea or a rash. While far less common, few people infected will develop serious illnesses, such as encephalitis (inflammation of the brain). People age 60 and older and those with certain medical conditions are at greater risk for serious illness. 

“We expect to find West Nile virus in mosquito pools during the summer months,” said State Public Health Veterinarian Natalie Kwit. “Fortunately, most people infected will never have symptoms, and cases of West Nile virus have been rare in Vermont. But West Nile virus and other diseases spread by mosquitoes can be serious for some people, and there’s no vaccine or specific medicines available for West Nile virus infection. The best protection is to take simple measures to protect yourself and family from mosquito bites.”

The Health Dept. offers tips to prevent mosquito bites: 

Wear long-sleeved shirts and pants when outdoors.

Limit your time outside at dawn and dusk when mosquitoes are more likely to bite. 

Use insect repellent labeled as effective against mosquitoes. The EPA has a tool to help find the right repellent. These can also protect for ticks.  

Get rid of standing water in places like gutters, tires, play pools, flowerpots and bird baths. Mosquitoes breed in water standing more than four days. 

Cover strollers with mosquito netting. 

Fix holes in screens and make sure they are tightly attached to doors and windows.  

Horse owners should consult with their veterinarians and make sure their animals are up to date on vaccinations for this and other diseases spread by infected insects or ticks. Horses cannot spread West Nile virus to humans or other horses, but the virus can cause neurologic disease and death in unvaccinated animals. In 2018 an unvaccinated horse died from the virus. 

Mosquitoes are collected throughout Vermont by the Agency of Agriculture, Food and Markets and tested at the Health Department Laboratory. This interagency surveillance effort occurs every summer and early fall. 

For more information, visit healthvermont.gov/mosquito.