ADVERTISEMENT Officials at Clemson Livestock Poultry Health (CLPH) have confirmed a 15-year-old Shetland pony mare with Eastern equine encephalomyelitis (EEE). The mare, which resided in Clarendon County, was unvaccinated and is deceased. This is Clarendon County’s first case of EEE in an equine this year, and South Carolina’s 17th. EEE 101 Eastern equine encephalomyelitis is caused by the Eastern equine encephalitis virus, for which wild birds are a natural reservoir. Mosquitoes that feed on EEE-infected birds can transmit the virus to humans, horses, and other birds. Horses do not develop high enough levels of these viruses in their blood to be contagious to other animals or humans. Because of the high mortality rate in horses and humans, EEE is regarded as one of the most serious mosquito-borne diseases in the United States.