EEE in virginia horses

On Aug. 10 the Virginia Department of Agriculture and Consumer Services (VDACS) announced that a horse from Suffolk has tested positive for Eastern equine encephalitis (EEE). This is the first confirmed case of EEE in Virginia horses this year.

The affected Quarter Horse mare received treatment at the North Carolina State University College of Veterinary Medicine large animal hospital in late July, however she subsequently died. The hospital received the positive EEE test result yesterday Aug. 9.

The mare was incompletely vaccinated. That is, she had received initial vaccination against EEE, but not the follow-up booster, the VDACS said.

EEE 101

A viral disease, EEE is transmitted to equids by infected mosquitoes and causes brain and spinal cord inflammation. Once a horse is bitten by an infected mosquito it can take three to 10 days for clinical signs to appear. Such signs can 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 are a very effective EEE prevention tool. 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 unknown vaccination histories, however, should receive the initial two-shot vaccination series within a three- to six-week period.

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

  • Removing stagnant water sources;
  • Dumping, cleaning, and refilling water buckets and troughs regularly;
  • Keeping animals inside during the bugs’ feeding times (typically early in the morning and evening); and
  • Applying mosquito repellents approved for equine use.