Another Kentucky horse has tested positive for West Nile virus (WNV), E.S. Rusty Ford, equine operations consultant for the Kentucky State Veterinarian’s Office, said in an Oct. 2 statement. There are now eight confirmed cases of WNV in Kentucky horses this year.
The horse—a 3-year-old filly from Fayette County—presented on Sept. 28 with acute progressing ataxia (incoordination). Ford said she could rise and stand with assistance, but was not drinking, was hypersensitive to touch, and had muscle fasciculation (twitching) on her muzzle and triceps. As of Oct. 2, the fill is reportedly much improved with a favorable prognosis.
Ford said the filly had been vaccinated against WNV in 2016 and 2017 but had no WNV vaccination history reported in 2018.
In 2017 there were 16 reported cases of WNV in Kentucky horses, Ford told The Horse.
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.