BELCHERTOWN — The Massachusetts Department of Public Health announced that a mosquito sample from Belchertown tested positive for Eastern equine encephalitis (EEE) virus, a rare but potentially fatal viral disease.

The sample taken on Monday, July 21, is the first identification of EEE in Massachusetts this season. In 2024, four human cases and four horse cases of EEE were reported last summer, along with one death. No contracted cases in humans or animals have been reported this year, the state said.

“This is around the time we would expect to find EEE in mosquitoes in Massachusetts, especially after an active EEE season last year with four recorded human cases,” Public Health Commissioner Robbie Goldstein said in a statement. “This is only a first finding and mosquito surveillance will be key to tracking any developing areas of increasing risk. Today’s finding is an important reminder for residents to take measures to protect themselves from mosquito bites.”

DPH’s fact sheet on EEE said the disease spreads through infected mosquitos that pass the virus through bites. Since 1938, there has only been about 115 cases of EEE in Massachusetts, with outbreaks occurring every 10 to 20 years. The CDC reports that severe cases cause neurological diseases or death. Roughly half of the people who contracted severe cases of EEE in Massachusetts have died.

“EEE activity in Massachusetts tends to occur in outbreak cycles,” State Epidemiologist Dr. Catherine M. Brown said.

“When EEE is found in mosquitoes at this point in the season, the risk may increase throughout the rest of the summer. We rely on our mosquito surveillance program to monitor for the presence of virus to let people know when and where the risk is occurring.”

The state suggests that residents use bug spray, wear long clothing and avoid the outdoors during dawn or dusk to prevent mosquito bites.

People can also mosquito-proof their homes by draining standing water and installing screens on windows and doors. Horse owners should keep their animals indoors if possible and speak to veterinarians about bug repellents.

Emilee Klein can be reached at eklein@gazettenet.com.