Mosquitoes trapped in North Stonington, Stonington and Voluntown recently tested positive for eastern equine encephalitis, a rare but deadly virus.

Ledge Light Health District and Uncas Health District announced the positive tests in a news release on Tuesday. Some of the mosquitoes trapped are species known to bite humans. Last week, state health officials noted mosquitoes infected with the virus were detected in Voluntown and Madison.

EEE-infected mosquitoes that bite humans and other mammals were found in a mosquito trap in a swamp behind Stonington High School on Aug. 20 and near Exit 93 of Interstate 95 on the Stonington-North Stonington border on Aug. 21, Matthew Cartter, state epidemiologist and director of infectious diseases, wrote in an email to Stephen Mansfield, director of health for Ledge Light Health District. Infected mosquitoes known to bite birds also were found behind the high school, at Exit 93 and at the Barn Island preserve in Stonington.

Cartter called the findings of EEE behind the high school "very concerning."

The virus can cause serious illness affecting the brain, the state Department of Public Health said in a release issued Tuesday evening. The disease is fatal in 25 percent to 50 percent of cases and many people who survive suffer from lasting health problems. Symptoms include high fever, headache, stiff neck and decreased consciousness, and anyone with these symptoms should contact their physician immediately, the release said. No human vaccine or specific antiviral treatment for clinical EEE virus infections are available, DPH said. 

The health districts advised residents of the towns to avoid outdoor activities from one hour before to one hour after both dawn and dusk.

Other precautions include ensuring tight-fitting windows, wearing shoes, pants and long-sleeved shirts, and using mosquito repellent. Disposing of water-holding containers like ceramic pots, used tires and clogged gutters can reduce mosquitoes around the home. The health officials also advise residents clean and chlorinate swimming pools and cover them when not in use, and to drill holes in the bottom of containers.

The disease has been found in trapped mosquitoes in Connecticut but only one person has ever died from it in the state, officials said.

Additional resources on the virus and mosquito management can be found at bit.ly/CTmosquito.