Vets Confirm Idaho's First 2019 Equid WNV Case
On July 26, Idaho Department of Agriculture (ISDA) veterinarians confirmed the state’s first 2019 case of West Nile virus in Payette County. One of two exposed equids, a suckling donkey filly, first experienced clinical signs on July 22. Being just 2 ½ months old, the filly had not yet received vaccination against WNV.

“Vaccination is shown to be efficacious in, if not preventing, then certainly lessening the severity of the infection and the adult horse’s recovery time,” said Bill Barton, DVM, Idaho’s State Veterinarian/Administrator.

The last confirmed equine WNV case in Idaho involved an 11-year-old Quarter Horse mare in Bingham County in September 2018. The Idaho Department of Agriculture confirmed five equine cases of WNV in 2018: one each in Bingham, Canyon, Clark, Jerome, and Owyhee counties. No human cases have been confirmed in Idaho in 2019.

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

WNV 101

Clinical signs of WNV in horses include:

  • Flu-like 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’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.