EEE Identified in Florida, Georgia Horses

A horse in Palm Beach County, Fla., and a horse in Lanier County, Ga., have both tested positive for Eastern equine encephalitis (EEE), according to local news reports.

The Palm Beach Post reported that the Florida horse, who was located in Wellington, was euthanized before testing positive for EEE on June 29.

Local news station WALB reported July 2 that Georgia animal health officials said the affected horse in Lanier County was the fourth EEE case confirmed in that state this year.

The USDA Animal and Plant Health Inspection Service National Animal Health Surveillance System said six EEE cases were confirmed in Florida horses in 2011 and none were reported in Georgia.

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. Its fatality rate 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.

The American Association of Equine Practitioners recommends vaccinating horses against EEE annually. Their vaccination guidelines for different classes of horses suggest:

  • Previously vaccinated adult horses should be vaccinated annually each spring before mosquito season begins. Veterinarians in geographic areas conducive to mosquito activity year round might suggest vaccinating against the disease in the fall as well.
  • Adult horses previously unvaccinated or with an unknown vaccination history should receive two doses, four to six weeks apart, before being placed on the same schedule as previously vaccinated adult horses.
  • Previously vaccinated pregnant mares should be vaccinated four to six weeks prior to foaling.
  • Previously unvaccinated pregnant mares or those with an unknown vaccination history should receive a two dose series (four weeks apart) immediately, and should receive a booster either four to six weeks prior to foaling or before the start of mosquito season, whichever comes first.
  • Foals of previously vaccinated mares should receive a three-dose series beginning at four to six months of age. The third dose should be administered at 10 to12 months of age, prior to the start of the next mosquito season.
  • Foals of unvaccinated mares or mares with an unknown vaccination history should also receive a three-dose series, starting at three to four months of age, with a 30-day interval between the first and second doses and a 60-day interval between the second and third doses.
  • Naturally infected and recovered horses are believed to have lifelong immunity to the disease, so only consider vaccination if the animal's immune status changes (such as with long-term corticosteroid use or with the onset of certain diseases).

Work with your veterinarian to ensure all horses' EEE vaccinations are current before peak mosquito season begins.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in three-day eventing with her OTTB, Dorado.

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