Washington’s state veterinarian has confirmed three horses with West Nile virus (WNV): two in Yakima County and one in Kittitas County.

One Yakima County horse was unvaccinated and is deceased. It resided at a private facility. The second horse in that county was undervaccinated and is recovering. It resides at a private facility. The number of exposed horses is not known.

The Kittitas County horse, which resided at a private facility, was euthanized. It had been recently purchased and its previous vaccination history is unknown. It had spent the last month at Southern Idaho rodeos.

About West Nile Virus

WNV transmission occurs when infected mosquitoes feed on animals, as well as humans, after having fed on infected birds.

Clinical signs of WNV in horses include:

• Mild anorexia and depression
• 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);
• 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%. The American Association of Equine Practitioners includes WNV as one of the core diseases all horses should be vaccinated against at least annually.