California Horse Confirmed With WNV

On Nov. 13, officials at the California Department of Food and Agriculture (CDFA) confirmed a horse in Sacramento County with West Nile virus (WNV). The affected horse, an undervaccinated yearling Thoroughbred colt, began showing clinical signs on Nov. 3. Signs consisted of ataxia (loss of control of bodily movements) and hind-limb neurologic signs. The colt is recovering.

According to CDFA, this is California’s 19th confirmed equine case of WNV in 2020. Other counties with confirmed cases include: Amador (2), Butte (1), Glenn (1), Kinds (1), Merced (1), Modoc (1), Nevada (1), Riverside (2), San Bernardino (1), San Joaquin (4), and Stanislaus (3).

Of the 19 confirmed cases, 13 were unvaccinated, four had unknown vaccination histories, and two were vaccinated. Fourteen are alive, one died, and four were euthanized.

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.