Two Cases of EEE Found in June in South Carolina Horses

Eastern equine encephalitis (EEE) was confirmed in two South Carolina horses in June, said Boyd Parr, DVM, state veterinarian and director of Clemson University's Livestock Poultry and Animal Health programs.

A 10-year-old horse from Horry County and a 4-year-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 often is preventable by via vaccinations. Horse owners are urged to consult their veterinarian to ensure vaccinations against both EEE and West Nile virus are up-to-date, he said.

"These June 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 blacktailed mosquito. Two to three days after becoming infected with the 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, EEE 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.

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. The fatality rate for EEE in horses is 75-95%. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care. Horses that survive might have long-lasting impairments and neurologic problems. Clinical signs of EEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures.

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

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