The Idaho State Department of Agriculture (ISDA) has confirmed a horse on a Blaine County farm with West Nile virus (WNV) on Aug. 20. The affected horse, a 9-year-old Quarter Horse gelding, who had not been vaccinated against WNV, first experienced clinical signs of the disease on Aug. 13. Signs included severe ataxia (incoordination) and abrasions on his limbs from being down. He is reportedly recovering.

In addition to Blaine County, the ISDA has confirmed WNV in horses in Lemhi, Twin Falls, Canyon, and Ada counties.

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.