Fifth Case of WNV Confirmed in California for 2020
On Aug. 24, officials at the California Department of Food and Agriculture (CDFA) confirmed the state’s fifth case of West Nile virus (WNV) this year. The affected horse, an 8-year-old Andalusian stallion from Riverside County, experienced onset of clinical signs on Aug. 12. Signs included fever, hind limb ataxia (loss of muscle control), and proprioceptive (perception of body position) deficits in his limbs. The horse, which was unvaccinated, is recovering.

According to a CDFA statement, this is California’s fifth confirmed case of WNV in 2020. Other positive horses were from Amador (1), Merced (1), San Joaquin (1), and Stanislaus (1) counties. Three of the five were unvaccinated, and two had unknown vaccination histories. Three horses have survived, one died, and one was 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.