Mosquitoes trapped in Colchester on October 14 tested positive for eastern equine encephalitis (EEE) virus, the first EEE-positive mosquitoes the Connecticut Agricultural Experiment Station (CAES) has identified in the state this year, the State of Connecticut Mosquito Management Program announced.

The positive mosquitoes were Culex pipiens, a predominantly bird-biting species. CAES operates 108 mosquito-trapping stations in 88 municipalities, trapping and testing from June into October and reporting positive findings to local health departments. Dr. Philip Armstrong, chief scientist at CAES, said: “Although the weather has cooled and mosquito populations are declining to low levels, the late season detection of EEE virus in eastern Connecticut warrants attention. Residents should continue to take measures to prevent mosquito bites, especially during episodes of unseasonably warm weather.”

EEE is a rare but serious illness in humans, with 4 to 8 cases reported in a typical year in the U.S. It is the most severe mosquito-transmitted disease in the country, with approximately 40 percent mortality and significant brain damage in half of survivors. The last major outbreak, in 2024, involved 19 human cases nationally.

The Mosquito Management Program is a collaborative effort among the Department of Energy and Environmental Protection, CAES, the Department of Public Health (DPH), the Department of Agriculture and the University of Connecticut’s veterinary diagnostic laboratory.

“The detection of EEE virus in mosquitoes in Colchester is a reminder that mosquito-borne illness can still occur in Connecticut even late in the season,” said Manisha Juthani, M.D., commissioner of DPH, “EEE is rare, but it is a serious illness, and the risk of human infection, while low, is not zero until we have a hard freeze. DPH encourages residents to keep taking simple precautions in the days ahead: use an EPA-registered mosquito repellent, cover bare skin when outdoors at dusk and dawn, and make sure window and door screens are in good repair.”

Residents can reduce bites by limiting time outdoors between dusk and dawn, wearing light-colored, loose-fitting clothing treated with permethrin, and covering strollers and baby carriers with mosquito nets.