What is Eastern Equine Encephalitis?

The Basics of Eastern Equine Encephalitis

Eastern equine encephalitis, also referred to as eastern equine encephalomyelitis or EEE, is an avian virus that can be communicated to humans and horses through mosquito bites. Cases of EEE are primarily seen on the eastern seaboard of the United States between New England and Florida. EEE is most prevalent in southern coastal regions due to the prime mosquito breeding conditions. New cases of EEE are commonly seen during warm summer months.

The virus originates in birds and is transmitted through the bird population by mosquito bite. The virus does not harm birds. However, when a mosquito bites an infected bird and then transmits the disease to a horse or human, the prognosis for a full recovery is very poor. Fortunately, human cases of EEE are extremely rare, and there is a vaccine available to protect equines. Humans and horses cannot spread the disease in any way. The only way for a human or animal to contract EEE is through the bite of an infected mosquito.

EEE and Horses

When an unvaccinated horse is bitten by a mosquito carrying EEE, the virus will attack the animal's central nervous system. The systems of EEE appear very suddenly in horses, and the disease is normally fatal in equines. Symptoms of EEE in horses include a general unsteadiness in movement, loss of coordination, erratic behavior and seizures. Horses that contract EEE normally die without two to three days of showing the first symptoms of the disease. As of 2010, there is no known effective treatment for the disease, though some horses do recover.

Preventing EEE

The vaccine for eastern equine encephalitis is extremely effective at preventing the disease from occurring. A regularly scheduled vaccination program is the very best defense against EEE. All horses residing in areas where EEE is a prevalent threat should receive an annual EEE vaccination in the spring just prior to peak mosquito breeding season, according to the American Association of Equine Practitioners. The AAEP recommends that pregnant mares, foals, and horses believed to have low immunity or high risk should have additional doses of the EEE vaccine administed.

In most parts of the country, the combined vaccine for EEE and the very similar western equine encephalitis (WEE) are given as part of a standard core vaccination program. WEE is a similar virus that occurs primarily in the western regions of the United States