SHELTON — A mosquito trapped in the city was found to be infected with Eastern Equine Encephalitis, state experts announced Wednesday. It is the first mosquito in Fairfield County to test positive for the illness in roughly 10 years.

The mosquito, was trapped Aug. 26 at the Shelton Avenue trapping site monitored by the Connecticut Agricultural Experiment Station. The finding is unusual, as Eastern Equine Encephalitis is more common in the eastern part of the state, said Philip Armstrong, research scientist and director of the mosquito surveillance program at the Connecticut Agricultural Experiment Station.

Indeed, of the 64 mosquitoes that have tested positive for Eastern Equine Encephalitis this season, nearly all have been outside of Fairifield County, in such towns as Voluntown (where 24 mosquitoes have tested positive this season) and North Stonington (which has had 17 mosquitoes test positive for Eastern Equine Encephalitis).

“EEE virus is more common in eastern CT but we occasionally pick it up in mosquitoes from Fairfield County too,” Armstrong said in an email. “The last time was ten years ago.”

He said, unlike West Nile Virus, Eastern Equine Encephalitis virus occurs primarily in rural parts of the state.

“The focal areas are forested swamps where the main mosquito vector resides,” Armstrong said. “These habitats are more extensive in the southeastern portion of the state.”

Though West Nile is usually the main mosquito-borne illness during the summer in Conencticut, West Nile activity has been relatively light this season, with only about 40 mosquitoes testing positive for the illness. So far, Armstrong said, Eastern Equine Encephalitis has been the dominant mosquito-borne illness this year.