West Nile Virus

What is West Nile Virus (WNV)?

West Nile Virus is a mosquito-transmitted arbovirus that causes inflammation of the brain and spinal cord. The mortality rate of horses with the virus is about 33%.

Can an infected horse transmit the virus to other horses?

No. West Nile Virus is not contagious to other horses because horses are “dead-end” hosts (they can get the virus but cannot spread it). However, infected mosquitoes and birds can continue to spread the virus.

What are the clinical signs of West Nile Virus in horses?

  • Changes in behavior
  • Loss of appetite
  • Depression
  • Intermittent weakness and paralysis
  • Fever
  • Muscle tremors
  • Incoordination/ataxia
  • Hypersensitivity
  • Facial nerve or other paralysis

What can I do to prevent West Nile Virus?

  • Vaccinate your horses for WNV at least once per year. In Florida and Southeastern states with a larger mosquito population, many recommend vaccinating every six months. Consult with your veterinarian.
  • Remove sources of standing water in pastures on your property.
  • Apply fly masks, fly sheets and/or fly leggings to horses when they are at pasture.
  • Spray horses with insect repellent.
  • Keep horses inside during the hours around dawn and dusk. These are the peak feeding times for mosquitoes.
  • Turn fans on in barns for stalled animals or open barn windows to create a breeze. The more powerful the fan, the better the protection.
  • Don’t forget to protect yourself by using insect repellent or wearing protective clothing.

What if my horse becomes infected with West Nile Virus?

If you think your horse may be infected with West Nile Virus, call your veterinarian or contact the UF Large Animal Hospital at (352) 392-2229 immediately.

Other mosquito-borne illnesses

House and Foal

Information provided by Dr. Amanda House, Veterinarian, UF Large Animal Internal Medicine service, Clinical Assistant Professor at the UF College of Veterinary Medicine, Diplomate of the American College of Veterinary Internal Medicine.

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