Oregon Confirms Two Horses With WNV

The affected horses, a 2-year-old Quarter Horse filly and a 3-year-old Quarter Horse mare, have unknown vaccination status.
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Malheur County, OR
On Sept. 15, officials at the Oregon State Veterinarian’s office confirmed two horses at a private facility in Malheur County with West Nile virus (WNV) | Photo: wikimedia commons
On Sept. 15, officials at the Oregon State Veterinarian’s office confirmed two horses at a private facility in Malheur County with West Nile virus (WNV). Another horse is suspected positive.

The affected horses, a 2-year-old Quarter Horse filly and a 3-year-old Quarter Horse mare, have unknown vaccination status. The mare presented on Sept. 7 with weakness, lethargy, and staggering. The filly presented on Sept. 8 with acute-onset ataxia (incoordination) and facial sensitivity and reactivity. Both are reported as recovering.

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.

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