WNV in Virginia horses

The Virginia Department of Agriculture and Consumer Services (VDACS) confirmed a case of West Nile virus (WNV) in a Smyth County horse, the Equine Disease Communication Center (EDCC) reported Oct. 17. This is the fourth confirmed case of WNV in Virginia horses in 2018.

“An unvaccinated 22-year-old Tennessee Walking Horse gelding developed an abnormal gait on Oct. 8,” the EDCC said. “Serum from the horse was tested using by IgM Capture ELISA at the VDACS Warrenton Regional Animal Health Laboratory. The horse has slowly improved since onset with supportive therapy.”

In 2017 there was just one confirmed case of WNV in Virginia 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 twitching;
  • Hyperesthesia (hypersensitivity to touch and sound);
  • Changes in mentation, 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 (incoordination).

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);
  • Applying mosquito repellents approved for equine use; and
  • Using fly sheets, masks, and boots/leggings on pastured horses.