2019 Update on West Nile Virus in Horses

West Nile virus (WNV) is a mosquito-borne viral disease that can cause inflammation of the brain (encephalitis) or the lining of the brain and spinal cord (meningitis). It is transmitted from mosquitoes that feed on infected birds, and then bite animals or humans. Horses are at great risk, representing 96.9% of reported cases of West Nile virus among non-human mammals


The virus has been found in all of the continental United States, most of Canada and Mexico, and in several Central and South American countries. In the U.S, in the last 20 years, 25,000 cases of WNV in horses have been reported, and in 2018 there were 14 cases of equine West Nile virus in the U.S (reported as of Aug. 20, 2019), spanning 10 states. 


Fortunately, there are ways to protect your horse from West Nile virus. Keep reading to find out how to keep your horse safe, and what to do if your horse does contract the disease.

What are West Nile virus symptoms in horses?

Once a horse has been bitten by an infected mosquito, it takes 5 to 15 days for symptoms of West Nile virus to appear. Each horse is unique and may exhibit anywhere from no symptoms to a combination of them. Here are common signs of WNV in horses:


  • Stumbling
  • Weak limbs
  • Muscle twitching
  • Flu-like signs (the horse has loss of appetite and seems depressed)
  • Daydreaming or looking like they’re “just not with it”
  • Propulsive walking (moving forward, often without control)
  • Partial paralysis
  • In some cases, death

What should I do if my horse contracts West Nile virus?

Treatment is vital for any horse who contracts WNV. Consult a veterinarian immediately if you suspect your horse has the disease. Whether treatment will be conducted at home or in a clinical setting depends on how bad the virus is, and on your horse’s age and health. 

How is West Nile virus in horses treated?

Your veterinarian will ultimately direct the treatment of your horse, but you can make sure your horse is receiving enough fluids, which may require an IV if the horse can’t drink on its own. Horses that are unwilling to eat may also require intravenous feeding. Some horses with WNV are unable to rise. In these cases, slinging is recommended two to three times per day, which aids in circulation and helps prevent pressure point sores. Often, head and leg protection are also needed. 


Be aware that horses weakened with WNV sometimes develop other problems, like:


  • Joint infections
  • Tendon infections
  • Sheath infections
  • Pneumonia
  • Diarrhea

How long does West Nile virus last in horses?

Once a horse begins treatment for West Nile virus, the recovery time depends on the health and age of the horse. Many horses improve within 5 to 7 days after exhibiting clinical symptoms. However, 20-30% may show signs of neurological deficits for weeks. 

Is there a WNV vaccine for horses?

There is a West Nile virus vaccine, and it is recommended as an annual core vaccine for horses. The vaccine shots are only effective if given before exposure to the disease. 


The WNV vaccine consists of two doses, given three to six weeks apart. Sometimes a third dose is required. Full protection develops four to six weeks after the second dose, and maximum resistance can take from seven to 12 weeks.

Can West Nile virus in horses be cured?

West Nile virus has no cure, but some horses can recover with proper care. It’s estimated that 50% of WNV cases will fully recover, 17% will have incomplete recovery or a relapse, and 33% will die.

How do I prevent my horse from getting WNV?

West Nile virus is most prevalent from May to October. Not surprisingly, this is also when mosquitos are more abundant. The primary prevention of WNV is to make sure you vaccinate your horse every year. 


Other measures you can take include:

  • Eliminate mosquito breeding sites (get rid of areas of standing water or common places that collect water, like old receptacles, tires, and containers).
  • At least once a month, thoroughly clean livestock watering troughs.
  • Keep your horse indoors from dusk to dawn, during peak mosquito activity.
  • Use insect repellants on your horse to reduce the chance of being bitten.
  • Remove birds (including chickens) located close to your stable. 
  • In the evening or night hours, avoid turning on lights inside that stable that may attract mosquitoes. 

With the proper precautions, there are many things you can do to protect your horse from West Nile virus. You can improve your horse’s quality of life even more by using the best horse care products available at Equiderma. Choose from our all-natural, highly effective product line.

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