A white-tailed deer that exhibited neurologic symptoms and died on Aug. 12 in Lisbon was infected with the eastern equine encephalitis (EEE) virus, the state Department of Energy and Environmental Protection announced Wednesday.

EEE is a serious but rare illness caused by a virus transmitted by mosquitoes. It kills up to 25 to 50% of people in known cases and causes significant brain damage in half of survivors.

In a news release, Department of Public Health (DPH) Commissioner Dr. Manisha Juthani said individuals with possible symptoms of EEE should contact their physician immediately. There is no human vaccine or antiviral treatment for EEE.

But most people infected with EEE virus do not become ill, according to the state Mosquito Management Program website. Symptoms include high fever, fatigue, muscle aches, neck stiffness, tremors or confusion. Severe cases include inflammation of the brain, encephalitis, which can lead to coma, convulsions, and death.

No human or horse cases of EEE have been reported in Connecticut this year, although human cases have been documented in Massachusetts, Vermont and New Jersey.

EEE-positive mosquitoes have been documented by the Connecticut Agricultural Experiment Station in Canterbury, Ledyard, North Stonington, Sterling and Voluntown. The finding also indicates the EEE virus is present in mammal-biting mosquitoes, prompting Connecticut’s Mosquito Management Program to advise residents to take precautions such as wearing mosquito repellent and covering bare skin, especially during dusk and dawn, when mosquitoes are most active.