WNV in Kentucky horses

A 9-year-old Quarter Horse gelding from Pendleton County, Kentucky, tested positive for West Nile virus (WNV) on Aug. 28. This is the first confirmed case of WNV in Kentucky horses for 2018.

In a statement E.S. Rusty Ford, equine operations consultant for the Kentucky State Veterinarian’s Office, said the gelding is alive, in stable condition, and has a favorable prognosis.

Ford said the gelding presented on Aug. 23 with lower lip paresis and muscle fasciculation (twitching). During the following 48 hours, the gelding developed progressive hind-limb ataxia (incoordination) and became recumbent (unable to rise).

“The patient remains hospitalized under treatment tonight (Aug. 28) and continues to improve,” Ford said. “Earlier this evening the … gelding was found to be bright, alert, and responsive; able to rise with assistance and stand; and eating and drinking well.”

He said the horse was not vaccinated against WNV.

In 2017 animal health officials confirmed 15 cases of WNV in Kentucky horses, according to USDA Animal and Plant Health Inspection Service data.

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.