Kentucky animal health officials have now confirmed five equine cases of West Nile virus (WNV) this year.

Kentucky Equine Programs manager E.S. “Rusty” Ford said Murray State University’s Breathitt Veterinary Center confirmed two additional cases—one in a horse from Hart County in another in a Russell County horse—on Aug. 18.

In Hart County, an 8-year-old Tennessee Walking Horse gelding presented Aug. 13 with lethargy, muzzle twitching, muscle fasciculation (twitching) in the shoulders and chest, and mild hind-limb ataxia (incoordination). As of Aug. 18, the treating veterinarian reported the horse was continually improving, Ford said. The affected horse has no WNV vaccination history, he said.

In Russell County, a 3-year-old Thoroughbred gelding presented Aug. 14 with muscle fasciculation and mild ataxia that progressively worsened over a roughly 24-hour period. As of Aug. 18, Ford said the horse’s veterinarian reported that he was responding “favorably to treatment and improving rapidly.” The horse was “documented to have been vaccinated in 2015, thought to have been vaccinated in 2016, and received a single vaccination in spring 201,” Ford said.

From 2001 to 2016, Kentucky confirmed 728 cases of WNV in horses, Ford said. Of those, 96% (699) were not adequately vaccinated—they had not been vaccinated in the 12 months preceding disease onset or they’d only received an initial vaccination with no follow-up boosters. Ford said 30% of the confirmed cases (219) died or were euthanized.

West Nile is transmitted to horses via bites from infected mosquitoes. Clinical signs for WNV include 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 are daydreaming or “just not with it”; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and “spinal” signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia. Equine mortality rate can be as high as 30-40%.

Horse owners should also consult their private practicing veterinarian to determine an appropriate disease prevention plan for their horses. Vaccines have proven to be a very effective prevention tool. Horses that have been vaccinated in past years will need an annual booster shot; in areas with a prolonged mosquito season, veterinarians might recommend two boosters annually—one in the spring and another in the fall. However, if an owner did not vaccinate their animal in previous years, the horse will need the two-shot vaccination series within a three- to six-week period.

In addition to vaccinations, horse owners also need to reduce the mosquito populations and their possible breeding areas. Recommendations include removing stagnant water sources, keeping animals inside during the bugs’ feeding times, which are typically early in the morning and evening, and applying mosquito repellents approved for equine use.