West Nile Virus (WNV) is a mosquito-borne virus that is primarily a bird disease but can infect any mammal, including horses and humans. It’s maintained by infected birds in the wild as they contain a high level of the virus in their blood. Humans and horses are considered “dead-end hosts” since mosquitoes appear unable to ingest sufficient amounts of the replicating virus to allow it to be passed between humans or horses.
The clinical signs of WNV range from mild flu type symptoms to potentially fatal encephalitis (inflammation of the brain tissue). Many horses do not develop clinical signs of the illness and recover without incident. Horses that do show signs may develop a fever, appear dull, are lethargic or have inappetence. Some abnormal behaviors include incoordination, weakness, muscle twitches, seizures, lip smacking, and an inability to rise. You should consult your veterinarian if your horse exhibits any abnormal or neurological behavior to rule out WNV or other neurological diseases including rabies, equine herpes virus-1, eastern or western encephalitis, trauma, or other causes.
There is no anti-viral treatment for WNV so horses are supported with anti-inflammatories, nutritional and fluid support, and kept in a safe environment. The more neurologic signs a horse is showing the worse the prognosis.
The best way to protect your horse from WNV, eastern or western encephalitis or rabies is with annual vaccination and with regular mosquito control. The American Association of Equine Practitioners (AAEP) recommends that the WNV vaccine should be incorporated into your horse’s annual core vaccine protocol.
This column is sponsored by Polk Equine.
BIO: Dr. Katie Hennessy graduated from the University of Illinois College of Veterinary Medicine in 2008 with a degree in large animal health and equine medicine. She completed an advanced internship at The Equine Medical Center of Ocala and is currently the owner and practicing veterinarian at Polk Equine. Her expertise ranges from small and exotic creatures to large animals, specializing in equine medicine.