Washington State Vet Confirms Horse With West Nile Virus
The Washington state veterinarian confirmed on Oct. 15 that a Franklin County horse tested positive for West Nile virus (WNV). The 2-year-old Quarter Horse stallion, which is reported as having been vaccinated, first showed clinical signs of ataxia (incoordination) on Oct. 8 and is reported as affected and alive.

This marks the state’s second equine case of WNV this year. In late August, a Franklin County man was the state’s first confirmed human WNV case.

About West Nile Virus

West Nile virus 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 (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.

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.