The California Department of Food and Agriculture (CDFA) announced that on Sept. 7, a 2-year-old unvaccinated Andalusian stallion began experiencing clinical signs of West Nile virus (WNV), including fever and recumbency (down and unable to rise). The horse, from Madera County, was euthanized.
According to westnile.ca.gov, the confirmation marks the second equine WNV case in Madera County and the ninth in California in 2019, with seven counties affected.
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 the following.
• 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 is essentially incurable; however, some horses can recover with supportive care. Equine mortality rates can reach 30-40 percent. The American Association of Equine Practitioners includes WNV as one of the core diseases all horses should be vaccinated against at least annually.