The Equine Disease Communication Center (EDCC) reported Nov. 26 that the Tennessee State Veterinarian has confirmed two more cases of equine West Nile virus (WNV). According to Tennessee Department of Agriculture data, there are now 12 confirmed cases of WNV in Tennessee horses this year.
“An 8-year-old Saddlebred mare in Loudon County that had been vaccinated in March of 2018 was confirmed positive on Nov. 12, 2018, on IgM ELISA,” the EDCC said. “A 7-year-old Tennessee Walking Horse gelding of unknown vaccination status located in Monroe County was confirmed positive on Nov. 16, 2018, on IgM ELISA.”
There were three confirmed cases of WNV in Tennessee horses in 2017, according to USDA Animal and Plant Health Inspection Service data.
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 (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).
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.