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West Nile Virus: What Do Horse Owners Need to Know?



West Nile virus in horses

The West Nile virus is making the rounds in North America again. The Texas Department of State Health Services detected at least five cases just in 2017. It’s important for horse owners to know the dangers posed by it, and what to do about it.

West Nile Virus: What Do Horse Owners Need to Know?

West Nile Virus

Electron microscopy of a West Nile virus.

The West Nile virus spreads through the bite of certain mosquitoes. It affects humans and animals, including horses, and causes general inflammation of the central nervous system (encephalitis). Infection by West Nile does not always become dangerous, and some infected may not show any signs of infection.


Horses affected by West Nile may become clinically ill or remain asymptomatic, though infected. In those who become ill, the symptoms include:

  • loss of appetite and depression;
  • fever;
  • weakness in the hind limbs;
  • paralysis of hind limbs;
  • impaired vision;
  • general weakness;
  • aimless wandering;
  • head pressing;
  • seizures;
  • difficulty or inability to swallow;
  • persistent walking in circles;
  • hyperexcitability;
  • coma;
  • sudden death.

It affects all equine species, including mules and donkeys.


Mosquito: Aedes albopictus

Mosquitoes are vectors of the West Nile virus.

The West Nile virus spreads through mosquito bites. The mosquitoes themselves become infected after biting wild birds carrying the virus. Several birds may do so, including pigeons, though these do not seem to pass the virus on to mosquitoes. While it can infect pets and cattle as well as humans, there is no transmission between species other than birds. While mosquitoes can bite infected horses, it will not pass to other animals by itself. In Europe and Asia, certain ticks also spread the virus. That is not the case in the Americas.

Is there a cure for the West Nile virus?

There is no known cure for West Nile, but the disease may be treated. Horses are especially vulnerable to the virus and may die from it. In general, around 33% of the infected and ill horses die — which makes all the more important to prevent it. It is very important, if your horse shows symptoms, to identify whether it truly is the West Nile virus; other illnesses may have similar symptoms. Once identified, the authorities should be notified.


Of all animals, horses are the most likely to be infected and show clinical symptoms. There is a vaccine, which may be applied according to veterinary instructions. As there is no way to tell whether a horse was vaccinated or infected, owners must keep records if they vaccinate. Owners should report if their horses become infected, so the appropriate authorities will know the virus is in the area. It is important to note that vaccination against Eastern and Venezuelan encephalitis does not prevent West Nile. The horse has to take a specific vaccine.

Vaccination against the West Nile virus is necessary

There is a specific vaccine against the West Nile virus. Talk to your veterinarian about it.

The best way to prevent West Nile encephalitis is to prevent mosquitoes. To do so, remove all possible sources of stagnant water from your home, barn and surrounding areas. Mosquitoes need still, clear water to reproduce. Four days is enough for a shallow puddle to become a focus.

To prevent this from happening, you can:

  1. Get rid of tin cans, buckets, ceramic pots, etc., which may gather water.
  2. Overturn wheelbarrows and wading pools when not in use.
  3. Refill and drain out water troughs and buckets frequently (less than four days).
  4. Clean clogged roof gutters frequently. Also, prevent birds from nesting on roofs and stable rafters.
  5. Check the property for dead birds, and dispose of them securely. Wear gloves and use plastic bags when doing so.
  6. Add fish to water gardens and ornamental pools. The fish prevent mosquitoes from breeding.
  7. Check discarded tires for water.
  8. Drain recycling containers through the bottom. This prevents fluids and water from pooling at the bottom.
  9. Don’t turn incandescent lights at night inside the barn. Incandescent lights attract mosquitoes. You can use them outside to draw mosquitoes away from the horses.
  10. Attempt to reduce the number of birds around the stable. Pigeons are less dangerous, as they do not seem to spread the virus, but wild birds may carry.

Do not forget to report any cases of unusual dead birds (especially crows) to the responsible authorities. They may be infected. While several bird species carry the virus, only a few become ill from it. Crows and blue jays seem more vulnerable than other species.

Other than such preventative measures against the mosquito, you might want to check for repellents for the horses, and fogging the stables, in special during dusk and dawn hours, when mosquitoes become more active. The mosquitoes are at their low in spring, and at the height of summer. It’s especially important to prevent mosquitoes during those times.


The West Nile virus, although rare in the Americas, can become a serious threat if unchecked. Do not forget to vaccinate your horses, and take the preventive measures against mosquitoes! The latter is especially important to prevent infection in humans and pets as well.

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