According to Boyd Parr, state veterinarian and director of Clemson University Livestock Poultry Health, 2 cases of eastern equine encephalitis (EEE) were confirmed in 2 South Carolina horses in June [2012].

A 10-year-old horse from Horry County and a 4-month-old horse from Marion County recently tested positive for the disease. EEE is a serious, mosquito-borne illness in horses, which can also affect humans. EEE is preventable by vaccinating horses. Horse owners are urged to consult with their veterinarian to be sure vaccinations against both EEE and Western Nile virus are up-to-date.

“These June [2012] diagnoses of EEE are a vivid reminder of the threat this and other mosquito-borne diseases are to horses in our state, especially following this year’s mild winter,” said Parr. “Protecting horses through vaccination is very important this year.”

The EEE virus is maintained in nature through a cycle involving the freshwater swamp mosquito _Culiseta melanura_, commonly known as the black tailed mosquito [see photo at <http://extension.entm.purdue.edu/publichealth/images/mosquito/popups/mosquito06.jpg>. 2 to 3 days after becoming infected with EEE virus, a mosquito becomes capable of transmitting the virus. Infected mosquitoes that feed on both birds and mammals can transmit the disease to horses and humans.

According to the Centers for Disease Control and Prevention, eastern equine encephalitis is a rare illness in humans. Most persons infected with it have no apparent illness. Severe cases begin with the sudden onset of headache, high fever, chills, and vomiting. People who are concerned should contact their physicians.

In horses, clinical signs usually develop from 2 to 5 days after exposure and include stumbling, circling, head pressing, depression or apprehension, weakness of legs, partial paralysis, the inability to stand, muscle twitching, or death. 9 out of every 10 horses infected with EEE virus die from the disease.

Any livestock, including horses, displaying stumbling, circling, head pressing, depression, or apprehension must be reported to the state veterinarian at 803-788-2260 within 48 hours, according to state law.

Eastern equine encephalitis is a viral disease that primarily attacks horses. The virus can be passed from the mosquito to human beings as well. However, horses cannot pass the virus to humans.

Unfortunately the disease is often lethal to the horse, causing great upset to the owner. It is a disease easily preventable with a vaccine. The equine vaccine should be given about every 4-6 months in high risk areas, such as along the Atlantic and Gulf of Mexico coasts or in areas that have experienced flooding. This year (2011-12), there was a mild winter and more rain and likely standing water from many sources, especially along parts of the US eastern seaboard.

This is an early announcement for EEE. And based upon Hurricane Debby, it may get worse in regions hit by that storm. There is no vaccine for humans.