WNV in Ohio horses

The Ohio Department of Agriculture (ODA) reported Aug. 21 that two horses in Northeast Ohio have tested positive for West Nile virus (WNV). These are the first cases of WNV in Ohio horses identified this year.

The ODA said the affected horses were not vaccinated.

“My message to horse owners is simple: vaccinate your animals and you can protect against West Nile Virus,” said State Veterinarian Tony Forshey, DVM. “Vaccines are a proven and effective prevention tool and I encourage all owners to talk to their veterinarian to learn how they can easily keep their animals healthy.”

WNV 101

West Nile virus is endemic in the United States and Ohio has reported positive cases in horses each of the last few years. There were 14 confirmed cases of WNV in Ohio in 2017.

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 (twitching);
  • 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 (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. Full immunity takes several weeks to achieve.

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.