California Confirms Third West Nile Virus Case
On Aug. 12, California Department of Food and Agriculture (CDFA) officials confirmed the state’s third case of West Nile virus (WNV) for 2020. The affected horse, an unvaccinated 17-year-old gelding from Merced County, experienced onset of clinical signs on Aug. 7. Signs included fever, depression, ataxia (loss of control of bodily movements), and dragging his hind feet. The horse is deceased.

Other horses confirmed with WNV this year were from Amador and Stanislaus counties. Two were unvaccinated and one had a vaccination history that was unknown. The other two horses are still living.

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); 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.