Experimental studies have concluded that horses are dead-end hosts for West Nile virus, so an infected horse is not a threat to other horses or people. Infection does not always cause clinical disease in horses. However, when the virus does cause clinical symptoms in the horse, it can be very serious.
Clinical signs vary.
Some horses may appear depressed or listless. Approximately half of all horses that show more severe neurologic signs, recover. At this time, there is no vaccination for West Nile virus. However, stopping the bird-mosquito infection cycle with vector control is the key to protecting horses. The type of mosquito primarily responsible for West Nile virus transmission is the Culex spp which spends its entire life within a range of about 1000 yards of its breeding site.