West Nile Virus (WNV) is a viral disease in the Flavivirus family that can result in fever and neurologic disease. The virus can infect horses, humans, and many different species of birds. Clinical signs of the disease usually present within about 15 days after a bite from an infected mosquito.
https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/equine/wnv

