Third EEE Case Confirmed in South Carolina in 2019

Veterinarians have euthanized a 3-year-old Arabian-cross gelding in Sumter County, South Carolina, after he tested positive for Eastern equine encephalomyelitis (EEE). Clemson Livestock Poultry Health stated that this is South Carolina’s third case in 2019. Clemson officials announced the state’s first confirmed case, in Chesterfield County, on July 23.

Only one horse in South Carolina, also in Chesterfield County, was confirmed positive for EEE in 2018.

What is EEE?

EEE is a viral disease that affects the central nervous system and is transmitted to equids by infected mosquitoes.

Clinical signs in horses 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; and
  • Severe central nervous system signs, such as head-pressing, circling, blindness, and seizures.

The disease can progress rapidly, with death occurring two to three days after onset of clinical signs despite intensive care in some cases. Fatality rates can reach 75-80%. Equids that survive might have long-lasting impairments and neurologic problems.

Studies have shown that vaccines can help significantly reduce the risk of a horse contracting EEE. Horses vaccinated in past years will need an annual booster shot; in areas with a prolonged mosquito season, veterinarians might recommend two boosters annually—one in the spring and another in the fall. Horses unvaccinated in previous years or those with an unknown vaccination history should receive the initial two-shot vaccination series within a three- to six-week period. Immunity takes several weeks to achieve.

In addition to vaccinations, owners should work to reduce the mosquito populations and possible breeding areas and horses’ exposure by: