Horses in Six Colorado Counties Confirmed With WNV
WNV transmission occurs when infected mosquitoes feed on animals, as well as humans, after having fed on infected birds. | Photo: iStock
Colorado’s State Veterinarian has confirmed a total of nine horses in six counties with West Nile virus (WNV). The affected counties include Adams, Boulder, Elbert, Morgan, Otero, and Weld. At least ninety-nine additional horses were exposed.

The first horse, residing in Weld County, experienced onset of clinical signs on July 30 and was confirmed positive on Aug. 4. Seven additional horses were reported exposed there.

Next, a Boulder County horse presented with signs on Aug. 9 and was confirmed positive on Aug. 11. Eight additional horses were exposed.

An Adams County horse followed, first experiencing clinical signs on Aug. 10. The horse was confirmed Aug. 13. Two more Adams County horses presented with signs, one on Aug. 12 and one the following day. They were confirmed positive on Aug. 16 and Aug. 17 respectively. Eight additional Adams County horses were exposed.

On Aug. 12, one horse in Morgan County and one in Elbert County presented with signs. Both were confirmed positive on Aug. 16. Sixty-five additional horses were exposed in Morgan County, and none reported in Elbert County.

Then, on Aug. 23, a Weld County horse experienced signs and was confirmed Aug. 24. Eight additional horses were reported as exposed.

The latest horse confirmed, on Aug. 24, resided in Otero County and first presented with signs on Aug. 17. Three additional horses were exposed there.

Neither the vaccination status or the health status of the affected horses was reported.

About West Nile Virus

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

mosquitos
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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.