A horse in St. Johns County, Florida, has tested positive for Eastern equine encephalitis (EEE), the Equine Disease Communication Center (EDCC) announced. According to Florida Department of Agriculture and Consumer Services statistics, this is the first EEE case for both the county and the state in 2018.

“On Jan. 12, 2018, one horse in St. Johns County, Florida, was confirmed positive for EEE,” the EDCC said. “The 2-year-old Miniature Horse gelding became clinical on Jan. 10 and was euthanized on Jan. 16 due to a poor prognosis. The vaccination history is unknown.”

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. 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. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care; fatality rates reach 75-80% among horses. Horses that survive might have long-lasting impairments and neurologic problems.

Vaccines have proven to be a very effective EEE prevention tool. Horses that have been 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. However, if an owner did not vaccinate their animal in previous years, the horse will need the two-shot vaccination series within a three- to six-week period