The Washington State Department of Agriculture reported that a 5-year-old Quarter Horse from Grant County, has tested positive for West Nile virus (WNV), the Equine Disease Communication Center (EDCC) said Aug. 13. This is the first case of WNV in Washington horses for 2018.
“The horse may have had one vaccination and has a neurological deficit in the right rear” leg, the EDCC said. “The prognosis at this time appears to be favorable and the horse is receiving supportive care.”
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 are a very effective EEE prevention tool. 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.
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.