Mosquito-borne horse disease cases increase

Published: August 1, 2012

COLUMBIA — The number of cases of a serious horse disease has risen from two to six in South Carolina. The mosquito-borne illness has been found in Horry, Darlington, Marlboro, Kershaw and Marion counties.

The new cases of eastern equine encephalitis (EEE) were confirmed in July, adding to two reported in June, said Boyd Parr, state veterinarian and director of Clemson University Livestock-Poultry Health.

There were no cases reported last year and two reports in 2010. In 2003, there were 154 cases of EEE.

“It can get out of hand if we don’t vaccinate horses and control mosquitoes,” said Parr. “These diagnoses 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. Protecting horses through vaccination is very important this year.”

Horse owners are urged to consult with their veterinarian to be sure vaccinations against both EEE and West Nile Virus are up-to-date. One case of West Nile Virus was reported in a York County horse in June.

The EEE virus is maintained in nature through a cycle involving the freshwater swamp mosquito Culiseta melanura, commonly known as the blacktailed mosquito. Two to three 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, symptoms usually develop from two to five 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. Nine out of every 10 horses infected with EEE virus die from the disease.

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

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