WNV in Kentucky horses

Another Kentucky horse has been diagnosed with West Nile virus (WNV), E.S. Rusty Ford, equine operations consultant for the Kentucky State Veterinarian’s Office, said in an Oct. 19 statement. There are now 12 confirmed cases of WNV in Kentucky horses this year.

The University of Kentucky Veterinary Diagnostic Laboratory confirmed the diagnoses for a Magoffin County horse, Ford said.

The 5-year-old Kentucky Mountain Horse gelding presented on Oct. 10 with muscle fasciculation (involuntary twitching), lethargy, and inappetence. As of Oct. 17, the horse was described as much improved and has a favorable prognosis.

Ford said the horse had no WNV vaccination history.

In 2017 there were 16 reported cases of WNV in Kentucky horses, he told The Horse.

WNV 101

West Nile virus is transmitted to horses via bites from infected mosquitoes. Not all infected horses show clinical signs, but those that do can exhibit:

  • Flulike signs, where the horse seems mildly anorexic and depressed;
  • Fine and coarse muscle and skin fasciculation;
  • Hyperesthesia (hypersensitivity to touch and sound);
  • Changes in mentation (mentality), when horses look like they’re daydreaming or “just not with it”;
  • Occasional drowsiness;
  • Propulsive walking (driving or pushing forward, often without control); and
  • Spinal signs, including asymmetrical weakness; and
  • Asymmetrical or symmetrical ataxia.

West Nile has no cure, however some horses can recover with supportive care. Equine mortality rates can reach 30-40%.

Studies have shown that vaccines can be effective WNV prevention tools. Horses vaccinated in past years need an annual booster shot, but veterinarians might recommend two boosters annually—one in the spring and another in the fall—in areas with prolonged mosquito seasons. In contrast, previously unvaccinated horses require a two-shot vaccination series in a three- to six-week period. It takes several weeks for horses to develop protection against the disease following complete vaccination or booster administration.

In addition to vaccinations, owners should work to reduce mosquito population and breeding areas and limit horses’ mosquito 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.