California Officials Diagnose 15th Horse With WNV
On Oct. 9, officials at the California Department of Food and Agriculture (CDFA) confirmed a 5-year-old Azteca gelding from Tuolumne County positive for West Nile virus (WNV). The gelding first showed clinical signs, including hypermetria (an exaggerated gait), irregular gait, and muscle loss, on Sept. 2. His vaccination status is not known, and he is reported as affected and alive.

This is Tuolumne County’s first equine case of WNV for 2019. As of Oct. 11, 15 horses have tested positive in 12 California counties.

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 (twitching);
  • 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 (incoordination).

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.