West Nile Virus: Is My Horse At Risk? + Warning Signs

At the turn of the millenium emerged a scary infection, known as the West Nile Virus. This new and relatively unknown disease among the world’s population started causing horrendous flus in humans. However, humans were not the only ones impacted, as the virus was also affecting thousands of horses in grave ways.

Many horses who are exposed to the West Nile Virus will never display any symptoms. Thankfully, the majority (about 60%) of the affected horses will likely make a full recovery. However, learning more about this disease and its possible effects on your horse is undoubtedly the best first step towards preventing this nasty infection in the first place. Read on to find out more about West Nile Virus in horses.

History And Risk Factors Of West Nile Virus

History And Risk Factors Of West Nile Virus

The West Nile Virus emerged in Uganda in 1937. It made its first appearance in the United States in September of 1997, when the disease was discovered in the tissue of flamingos in the Bronx Zoo. West Nile Virus was soon also discovered throughout the New York City crow population. By 2002, the disease had spread to over 15,000 horses in 41 of the United States.

How could it have affected so many horses in that amount of time? After all, the West Nile Virus did not originate in horses. As it happens, West Nile Virus is a viral infection that is communicable between birds. As it spreads throughout various avian populations, mosquitoes will feed off their blood, which has a high potency of the virus in their system. The mosquitoes will then transmit the virus to humans or horses when finding their next feast.

Goats, sheep, dogs, llamas, bears, reptiles, and other animals can also contract the virus, although this is not as common. Since the disease emerged nearly a century ago, West Nile has spread throughout the entire world, but it occurs most naturally in arts of Africa, Asia, the Middle East, Europe, North America, Central America, Caribbean Islands, and South America.

Thankfully, the disease is not potent enough in human or equine blood to spread to other humans or horses, either by exposure or mosquito bite. So the only way that a horse or human can contract it is if the local bird population is carrying the virus during the mosquito life cycle (during the warmer months of the year).

Sometimes horses are not affected when exposed to the West Nile Virus. Others may contract West Nile Encephalitis, otherwise known as West Nile Fever.

Warning Signs + Diagnosis Of The West Nile Fever

Diagnosis Of The West Nile Fever

Like many equine ailments, West Nile Fever can display a host of symptoms that could otherwise be linked to other health problems. However, any of these warning signs should be cause for concern:

  • Stumbling, staggering, poor coordination, or loss of motor control in any part of their body (but especially their hind legs)
  • Twitching muscles, particularly the muzzle, lower lip, back, neck, shoulder, & pectoral
  • Loss of appetite
  • Weakness in back legs
  • Depression or excitability
  • Circling
  • Paralysis in any part of the body
  • Impaired vision
  • Inability to swallow

The West Nile Virus can breech the bloodstream and enter the brain and spinal column, so its symptoms are largely neurological in nature. Since many of these neurological issues could also be indicators of other infections or disorders, a vet will diagnose based not only on the displayed symptoms, but also a laboratory test to confirm the presence of the virus.

One type of laboratory test only requires a blood sample and searches for West Nile Virus antibodies in the bloodstream to make a positive diagnosis. Another type of test takes a tissue sample from the horse’s body to see if the disease is present.

Prevention + Treatment Of West Nile Virus In Horses

Treatment Of West Nile Virus In Horses

The West Nile Vaccine came out in 2003 in response to the rapid spread of the disease in the United States. The American Association of Equine Practitioners (AAEP) recommends that all horses be vaccinated at least once against the virus, considering the scope of the lifelong symptoms in horses.

The vaccine consists of two shots given three to six weeks apart. Your veterinarian may advise repeat vaccinations ranging from once per year to once every four months, depending on how prolific the West Nile Virus is in your region.

Another way to prevent the contraction of West Nile Virus is to manage the mosquito population around your horses. The most important measure is to remove muck and stagnant water sources regularly from the property, since they are prime breeding grounds for mosquitoes.

It can also be helpful to control weeds, keep fans and screens in the horse enclosures (mosquitoes don’t fly well in the wind), and to use equine insect repellent during the warmer months. Make sure to keep incandescent bulbs away from the stables, as these will also attract mosquitoes.

Veterinarians can prescribe pain medications, anti-inflammatory drugs, and sedatives to help lessen the impact of the painful and stressful neurological symptoms of West Nile Fever in horses. Unfortunately, there is no cure for West Nile Fever, but knowing the warning signs can help manage your horse’s quality of life should they contract it.

Many horses (up to 60%, in fact!) will fully recover from the virus without residual symptoms. For horses who don’t fully recover, the effects of the infection could also be helped to some degree by nutritional therapy. Horses with long-term affected mobility or coordination need to be supervised more carefully to avoid additional injury if at all possible.

Though the disease can cause life-altering and sometimes grave symptoms, not all horses get ill after contracting West Nile Virus. Knowing that you can improve your horse’s odds of fighting off the infection by staying up to date with recommended vaccines and preventative measures is fantastic news.

So as the beautiful summer months approach, remember to contact your vet about the risk of West Nile Virus in your region. Keep an eye on stagnant water sources, and always keep the equine bug repellent readily on-hand!


  1. https://aaep.org/horsehealth/west-nile-virus
  2. https://waddl.vetmed.wsu.edu/animal-disease-faq/west-nile-virus
  3. https://www.vet.k-state.edu/vhc/services/equine/timely-topics/wnv-fact-sheet.pdf

1 thought on “West Nile Virus: Is My Horse At Risk? + Warning Signs”

  1. Magnetic Resonance Imaging (MRI) is an imaging modality that utilizes magnetic forces within the patient’s cells to create a two-dimensional image. The way the images are created allows both bone and soft tissue structures to be seen with excellent detail. Additionally, information about the underlying disease process can often be obtained from the MRI image.


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