Evidence of the virus, more threatening than the Nile virus, has been linked to all three counties, according to the Division of Public Health.
Four chickens kept by the state have all tested positive for the virus.
Eastern Equine Encephalitis is a rare, potentially fatal viral disease that can affect both people and horses. While not as common as West Nile Virus, Triple E is more virulent, with a higher fatality risk, according to the Delaware Division of Public Health.
Symptoms often appear four to 10 days after being bitten by an infected mosquito. Severe cases can involve encephalitis, an inflammation of the brain, beginning with the sudden onset of headache, high fever, chills and vomiting.