Utah State University Extension
West Nile Virus (WNV) was first introduced to the United States in 1999. Since then, the disease has spread to all of our equine populations. Spread by mosquitos from infected birds to horses, WNV can cross the blood-brain barrier to cause an encephalomyelitis. Clinical signs can include weakness, ataxia, muscle twitching, coma, and even death. Prevention, by vaccination and reducing mosquito numbers, is much more effective than treating the disease.
Hoopes, Karl and Nay, Karah, "Equine West Nile Encephalitis" (2018). All Current Publications. Paper 1880.