California reports fifth equine West Nile virus case of 2026

A 3-year-old unvaccinated Quarter Horse gelding in Placer County, California, has tested positive for West Nile virus (WNV). The horse, which began showing clinical signs such as ataxia and hypersensitivity on August 4, is currently alive. This marks the fifth confirmed equine WNV case in California for 2026.

West Nile virus is transmitted to horses through mosquito bites. While not all infected horses exhibit symptoms, clinical signs can include muscle twitching, hypersensitivity to touch and sound, and spinal issues such as asymmetrical weakness. There is no cure for the virus, though some horses may recover with supportive care. Mortality rates for equine WNV can reach between 30% and 40%.