The West Nile virus (WNV) cases in humans and horses have been on the rise in 2012 and, according to the Centers for Disease Control and Prevention, human cases are at their highest levels since WNV was first detected in the United States in 1999. Tracy Norman, VMD, Dipl. ACVIM, clinical assistant professor at the Texas A&M University College of Veterinary Medicine & Biomedical Sciences Large Animal Clinic, suggests protecting horses by vaccinating against the disease and taking measures to prevent mosquito bites.

The virus is transmitted by mosquitoes from avian hosts to humans and horses. Both humans and horses are considered "dead-end" hosts, which means it is not contagious from horse to horse or horse to human. If bitten by an infectious mosquito, the virus can multiply in the blood system, cross the blood brain barrier, and infect the brain. There, it can cause inflammation of the brain, interfering with central nervous system functions.

Most horses infected with the virus do not exhibit signs of the disease. For those that do, however, symptoms are similar to other neurologic diseases and can include impairment of basic motor skills (including loss of coordination or asymmetrical weakness, a change in behavior, or drowsiness. Some horses with WNV can have a fever early in the disease and show symptoms such as sensitivity to touch and sound, and muscle twitching in the face, muzzle, and neck.

"These typical neurologic signs are not always present in infected horses, sometimes infected horses just appear colicky," Norman said. "You should always consult with a veterinarian if you suspect a horse of having West