Vesicular Stomatitis in Horses

Updated December 15, 2023 | Reviewed By: Jamie Whittenburg, DVM

What is Vesicular Stomatitis in Horses?

Vesicular stomatitis (VS) is a highly contagious viral disease that can affect horses, causing painful blisters or sores in the mouth, on the lips, or on the coronary bands. It can affect other livestock such as cattle and pigs, and in rare cases, infect humans. The disease spreads through direct contact with infected animals, contaminated objects, and biting insects. Vesicular stomatitis outbreaks can lead to quarantines, disruptions in shows, and require biosecurity measures to prevent its spread.

The disease is caused by the vesicular stomatitis virus (VSV), which belongs to the family Rhabdoviridae. There are different serotypes of VSV which can have varying symptoms.

Clinical Signs of Vesicular Stomatitis

In horses, vesicular stomatitis can manifest with a variety of clinical signs that may include:

• Oral lesions: The most common sign of the virus is the development of painful blisters or sores on the horse’s mouth. Blisters can form on the tongue, gums, inner cheeks, and lips. They can be painful for your horse and may rupture.
• Drooling and excessive salivation: Due to the discomfort caused by oral lesions, horses may drool excessively or have an increased production of saliva.
• Coronary band lesions: Blistering or ulceration are often found on the coronary bands (where the hoof meets the skin), which can cause lameness and a reluctance to move.
• Fever: An elevated body temperature means your horse is having an inflammatory response to the infection.
• Reluctance to eat or drink: The painful oral lesions can make it difficult for horses to eat and drink normally, resulting in a loss of appetite and dehydration.
• Lethargy and depression: Infected horses may seem depressed and have low energy.

The severity of these signs can vary from mild to severe, so it’s important to keep a watchful eye and call your veterinarian if you notice any indications of the disease.

Diagnosis

Veterinarians diagnose horses with vesicular stomatitis by examining their clinical signs, evaluating the horse’s history and possibility of exposure, as well as blood tests. A thorough physical examination is performed to assess the horse’s overall health and inspect any lesions on the skin.

Laboratory tests are crucial to the diagnosis and providing prompt treatment to prevent spreading the virus. Samples of the fluid from within the oral or coronary lesions will be collected and sent to a laboratory for evaluation. Additionally, PCR (polymerase chain reaction) tests may be used on blood samples to test for the presence of antibodies against VSV (this would indicate exposure or past infection).

Disease Transmission

VS is contagious and can be transmitted in several ways:

• Direct contact transmission: When an infected horse comes into contact with a susceptible horse, the virus may spread through saliva, nasal secretions, or fluid from ruptured blisters. This can happen when horses are near each other, such as being turned out in the same paddock, using the same bridle, touching noses in a breezeway, or through the stall bars.
• Contaminated objects: Feed troughs, water buckets, grooming tools, or tack used on an infected horse could be a source of transmission. The virus can live on these objects for a limited time.
• Biting insects: Flies, midges, and other insects can transmit vesicular stomatitis from an infected horse to a healthy horse.

While VS can infect people, transmission from horses to humans is rare. People can also contract VS through insect bites. Vesicular stomatitis in humans manifests as flu-like symptoms, including fever, headache, muscle aches, and fatigue. Any person that has been exposed and has any suspicion of disease should contact their doctor.

Treatment and Prognosis

Treatment for vesicular stomatitis is mainly supportive in nature to try to relieve the horse’s discomfort and promote healing. Your veterinarian may prescribe oral or topical pain-relieving medications to help relieve pain associated with the oral lesions. Since the lesions can become open sores, there is a risk of a secondary infection, and your vet may recommend antibiotics.

Feeding your horse soft, palatable food and providing clean water are important to ensure his nutritional needs are met, despite any difficulties in eating. If your horse is infected, he should be isolated to prevent spread to his barn mates. Biosecurity measures including hygiene protocols, disinfecting barn supplies and equipment, and insect control are crucial to minimize transmission.

Fortunately, the prognosis for a full recovery is generally good. Horses typically recover within a few weeks with the appropriate care. Keep in mind, your horse can remain contagious even after clinical signs have subsided. Veterinarians and animal health authorities closely monitor cases of VS to control and contain the disease.

Prevention and Management Best Practices

By implementing these preventative measures, you can help prevent a VS infection in your horse:

• Insect control: By minimizing exposure to biting insects, you can reduce the risk of transmission. Effective insect control measures include:
  • Fly repellents and insecticides.
  • Using fly sheets, boots, and masks.
  • Feeding supplements to help deter biting insects.
  • Decreasing the overall fly population with methods such as Fly Stoppers and feed-through supplements, removing manure, and getting rid of potential breeding grounds (like standing water).
• Biosecurity measures: Implementing strict biosecurity protocols at the barn is crucial if there is a confirmed case of VS. This includes controlling who comes and goes on the property, minimizing contact between horses and other animals, and practicing good hygiene (handwashing and using disinfectants).
• Quarantine and testing: Isolate any horse displaying signs and call your vet immediately. If you’re bringing a new horse to the barn, consider implementing a 21-day quarantine period. That way, you can observe the horse for any signs of illness before introducing them to the herd. Having your vet perform tests for VS and other diseases is also highly recommended – especially if they’re coming from areas known for VS.
• Avoid contamination: Avoid sharing equipment like feed and water buckets, grooming brushes, and tack between horses.
• Monitor outbreaks: Stay informed about outbreaks in your area and follow guidelines that agricultural authorities provide to keep horses safe.
  • Check the USDA Vesicular Stomatitis webpage for situation reports to see any recent cases across the country year-by-year.
  • Refer to your state’s agricultural office for equine health alerts and movement restrictions.
• Work with your vet: Recognizing the signs and promptly reaching out to your veterinarian to ensure your horse’s health. If you are hosting a show during an outbreak, require that owners provide a recent health certificate and provide a vet onsite to inspect horses when they enter the property.

Vaccinations

Currently, there are no approved equine vaccinations for vesicular stomatitis. Sunshine and heat are known to fight and quickly kill VS. Disinfectants like chlorine bleach are also effective for equipment surfaces.