A 22-year-old Quarter Horse gelding in Livingston County had to be euthanized last week after contracting West Nile virus.
The Michigan Department of Agriculture and Rural Development (MDARD) says the gelding, who was unvaccinated, began displaying clinical signs on November 28. He had a fever and ataxia, and was reportedly progressing to being unable to remain standing.
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 (involuntary twitching);
- Hyperesthesia (hypersensitivity to touch and sound);
- Changes in mentation (mental activity), 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 virus 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.
Officials say that 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 insect feeding times (typically early in the morning and evening); and
- Applying mosquito repellents approved for equine use.