The horse, a 7-year-old Paint gelding from Disputanta in Prince George County, moved to Virginia from Mississippi three months ago.
A blood test showed recent infection, and officials say he contracted the disease in Virginia. The horse, which had not been vaccinated for EEE, was euthanized on August 31.
This is the first reported case of EEE in a horse in Virginia this year. Last year, the state had eight cases of EEE, most of them from the Tidewater area which is typical, officials say.
So far, there have been no reported cases of West Nile Virus (WNV) in Virginia horses this year.