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Florida Equine EEE Cases Confirmed


Equine Disease Communication Center (EDCC) reported that animal health officials in Florida and Wisconsin have confirmed new cases of Eastern equine encephalitis (EEE) and officials in Washington have confirmed new West Nile virus (WNV) cases in horses in those states.

In Wisconsin, an unvaccinated 12-year-old Quarter Horse mare from Vilas County is the state’s fourth equine EEE case for 2016.

“The mare was febrile (had a fever), unable to rise, and unresponsive with various neurologic signs including extensor rigidity, struggling, nystagmus (involuntary eye movement), intermittent tonic/clonic activity (rapid succession of muscle contraction and relaxation; often associated with seizures), and frequent tooth grinding,” the EDCC said. “The attending veterinarian humanely euthanized the mare.”

In Florida, the EDCC reported that a new EEE case was confirmed on Sept. 19.

"The 11-year-old Quarter Horse mare was last vaccinated for EEE in late summer 2015, per the owner, and had no recent travel history," the EDCC said. "Clinical signs began on Aug. 13 and the horse was euthanized for humane reasons later the same day."

This is the first confirmed EEE case in Sumter County and Florida's 20th case for 2016.

Meanwhile, in Washington, the EDCC reported that the state Department of Agriculture has confirmed nine WNV cases—all in unvaccinated horses—thus far in September. The EDCC said the cases are as follows:

  • A 7-year-old Quarter Horse mare in Stevens County was confirmed positive on Sept. 1; prognosis is good.
  • A cross-bred gelding in Spokane County was confirmed positive on Sept. 3; prognosis is good.
  • A 12-month-old Quarter Horse-cross filly in Stevens County was confirmed positive on Sept. 4 and has since passed away.
  • A 2-year-old Arabian colt in Grant County was confirmed positive on Sept. 6; prognosis is good.
  • A 17-year-old gelding in Kittitas County was confirmed positive on Sept. 7; prognosis is good.
  • A 6-year-old Quarter Horse mare in Pend Oreille County was confirmed positive on Sept. 11; prognosis is fair.
  • A 23-year-old Arabian-cross mare in Okanogan County was confirmed positive on Sept. 11 and has been euthanized.
  • A 13-year-old Paint gelding in Franklin County was confirmed positive on Sept. 12 and has been euthanized.
  • A 5-year-old Arabian-cross mare in Spokane County was confirmed positive on Sept. 13; prognosis is good.

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.

West Nile is also transmitted to horses via bites from infected mosquitoes. Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations (twitching); hyperesthesia (hypersensitivity to touch and sound); changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia. Equine mortality rate can be as high as 30-40%.

Horse owners should also consult their private practicing veterinarian to determine an appropriate disease prevention plan for their horses. Vaccines have proven to be a very effective prevention tool. Horses that have been vaccinated in past years will need an annual booster shot. 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.

In addition to vaccinations, horse owners also need to reduce the mosquito populations and their possible breeding areas. Recommendations include removing stagnant water sources, keeping animals inside during the bugs’ feeding times, which are typically early in the morning and evening, and using mosquito repellents.

Larson, Erica. “New Equine EEE, WNV Cases Confirmed.” The Horse, September, 2016.