Addison County Horse Tests Positive for Eastern Equine Encephalitis

State also reports first human case of West Nile Virus this year 

WATERBURY, VT — The Department of Health continues to urge residents to take steps to prevent mosquito bites after an Addison County horse tested positive for Eastern equine encephalitis (EEE) last week. The horse, which was tested on Sept. 23, was unvaccinated and is now deceased. EEE, which spreads through the bite of an infected mosquito, is rare but can cause serious and life-threatening illness in people and some animals. Although the risk is lower as temperatures cool and mosquitoes are less active, prevention is still important. 

The town of Salisbury has been added to the list of high-risk towns where health officials strongly recommend limiting evening outdoor activities until the first hard frost in their area. High-risk towns now include Alburgh, Burlington, Colchester, Salisbury, Sudbury, Swanton and Whiting. 

One person tested positive for EEE in Chittenden County last month — the first human case in Vermont since 2012. Risk levels in towns are determined by a case in a human or mammal, or by the results of mosquito testing. From July to mid-October, the Vermont Agency of Agriculture, Food & Markets collects mosquitoes at various locations around the state, which are tested weekly at the Department of Health Laboratory. 

Most people infected with EEE virus do not develop symptoms, but those who do may experience a flu-like illness with fever, chills, body aches, and joint pain. About 5% of people who are infected develop severe EEE disease with encephalitis, an inflammation of the brain. Severe EEE disease is fatal in about one-third of people. 

The Health Department is also reporting the first case of West Nile virus in a person this year. The patient, a Chittenden County resident in their 80s, was hospitalized in August and discharged. The Centers for Disease Control and Prevention confirmed test results Sept. 25. 

West Nile virus causes less severe illness than EEE, and most people do not develop symptoms. Those who do may have a fever, headache, body aches, vomiting, diarrhea, or rash. Anyone with symptoms of either disease should reach out to their health care provider. There are no vaccines or treatments for West Nile or EEE.

Everyone in Vermont should take steps to prevent mosquito bites and protect themselves from mosquito-borne illness:

• Limit the amount of time you spend outdoors at dawn and dusk.
• Use EPA-registered insect repellent labeled as effective against mosquitoes. Apply repellent when you are going to be outdoors, especially at dawn or dusk.
• Wear loose-fitting long-sleeved shirts and long pants when outdoors.
• Fix any holes in your screens and remove standing water around your home.

Officials continue to evaluate options for aerial or ground spraying of pesticides in areas where infected mosquitoes have been identified, should that be deemed the best course of action to protect public health. The public will be notified in advance if spraying occurs.

Horse owners should consult with their veterinarians and make sure their animals are properly vaccinated for EEE, West Nile and other viruses spread by infected insects or ticks. Horses cannot spread EEE or West Nile viruses to humans or other horses.

So far this season, 3,863 groups of mosquitoes have been tested. There have been 82 groups that tested positive for the EEE virus and 63 that tested positive for the West Nile virus.

Learn more about mosquito surveillance: Healthvermont.gov/disease-control/mosquito-borne-diseases/mosquitoes-vermont.

For more info on preventing mosquito bites visit: HealthVermont.gov/mosquito.