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West Nile Virus in Horses

West Nile Virus (WNV) is a small virus that can affect both humans and horses. The virus is a mosquito-borne disease that can cause Encephalitis. Most of us are familiar with the Eastern and Western Encephalitis viruses in horses, but don’t think about West Nile Virus Encephalitis. West Nile Encephalitis is described as an inflammation of the central nervous system. Younger and older individuals are the most susceptible to the virus.


Mosquitoes bite, or take a blood meal, from wild birds that are infected with West Nile and pick up the virus. These mosquitoes can then transmit the virus to people and other animals when biting. Infections occur primarily in the late summer or early fall, but can happen any time during the mosquito season. Migratory birds are thought to spread the disease, and accounts in the late summer to fall increase near migration areas. Recently, the incident has increased in many states; this is alarming as treatment is not easy and not always successful.


West Nile Virus exposure does not always lead to signs of illness in people or animals. Some common signs in horses include:
  • Fever
  • Weakness of hind limbs
  • Paralysis of hind limbs
  • Impaired vision
  • Ataxia (weakness)
  • Head pressing
  • Aimless wandering
  • Convulsions (seizures)
  • Inability to swallow
  • Walking in circles
  • Hyperexcitability
  • Coma
West Nile can cause any or all of the above signs. Your horse should be examined immediately by a veterinarian if he starts exhibiting them. Many other diseases, including Eastern and Western Encephalitis, can mimic WNV. From clinical signs, it is hard to tell what Encephalitis causes without spinal fluid testing.


Treatment is difficult and involves supporting the horse until they can fend off the virus. It is important to note there is no specific treatment for WNV. That makes prevention even more vital to your horse’s health.


Vaccination against WNV is the only protection available for horses. We recommend Prestige V + WNV, a killed version of West Nile. Mosquito control is also important to protect animals and humans. Eliminate standing water and containers that hold standing water. Discourage birds from living around your stable. Use sprays that are safe for the environment to control the mosquito population. We like Adams Plus Yard Spray, Country Vet® Mosquito & Fly Spray, or Permethrin 10%. These products are long-lasting and work to kill mosquitoes.

There is no way to prevent mosquitoes from biting your horse, but you can prevent the virus from becoming an issue. There is a vaccine that can help protect horses from getting West Nile Virus disease. If you have not vaccinated for WNV, order the vaccine today. You and your horse will be glad you did!

If you need help, call us at 1-800-786-4751.

-Dr. B
Don Bramlage, DVM, Director of Veterinary Services at Revival Animal

The materials, information and answers provided through this website are not intended to replace the medical advice or services of your personal veterinarian or other pet health care professional. Consult your own veterinarian for answers to specific medical questions, including diagnosis, treatment, therapy or medical attention.

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For over 25 years, Revival Animal Health has been caring for people who care for pets by delivering quality, reliable products, along with customer service that's committed to your needs. Owners, breeders and shelters count on us because we too love pets, and provide the knowledge, understanding and genuine care it takes to keep them happy and healthy. We feel this is truly what it means to serve you with Pet Care from the Heart®.

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