Vesicular Stomatitis

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Also Known As



Vesicular stomatitis (VS) is a viral blister-forming disease affecting humans and livestock, including horses, cattle, sheep, goats, pigs, llamas, and alpacas. Vesicular stomatitis virus is the only one of the blister-forming viruses to affect horses, which differentiates it from other devastating diseases of livestock such as Foot and Mouth Disease (FMD). 

Vesicular stomatitis appears sporadically in the United States, where it is a reportable disease. A veterinarian diagnosing VS must report the case to the state and federal authorities, and the horse and property will be quarantined to avoid spread of the disease.

The incubation period is 2-8 days. Signs of VS in horses include a fever in the early stages, lethargy, and loss of appetite mainly due to the formation of vesicles, the blister-like sores, that form in the mouth. Vesicles are the primary distinguishing sign of VS and may form on the lips, tongue, gums, muzzle, sheath, teats, vulva, and at the coronary bands. 

The vesicles burst after a day or two leaving ulcerative sores. Horses with mouth lesions may avoid food and water and may drool copiously, in fact excess salivation is often one of the first signs noted. Horses with coronary band lesions may become lame, and weight loss is not uncommon.

The disease generally runs its course within two weeks. While it causes significant economic loss and pain/debilitation to the horse, VS is generally not fatal.


  • Fever,
  • Lethargy,
  • Loss of appetite,
  • Excessive salivation,
  • Blisters (vesicles) on mouth and body parts,
  • Ulcerative sores,
  • Weight loss,
  • Lameness,
  • Debilitation


VS is caused by the vesicular stomatitis virus. It may be spread by direct contact from an infected horse to another horse or to a human – via contact with ruptured vesicles. It may also be spread by buckets, feeders, and grooming supplies that contact infectious material from a sick horse.

Vesicular stomatitis tends to occur during the warmer parts of the year especially during fly season and the virus has been isolated from several species of biting flies. It is suspected that insects may transmit the disease from horse to horse.


Basic sanitation and biosecurity measures provide the best prevention against VS spread.  Infected horses should be quarantined and handled and fed last – after all of the healthy animals on the farm have been cared for. 

People handling infected horses should shower, change clothing, and disinfect all equipment after use. Latex gloves should be worn by those handling infected horses to reduce the risk of transmission between horses and from the horse to the handler.

Basic farm biosecurity should involve:

  • Fly and insect control
  • Individual feeders and equipment
  • Regular cleaning of feeders, waterers, trailers, and other equipment
  • Isolation of new horses for 21 days
  • Providing good nutrition and a regular exercise, vaccination, and deworming schedule since healthy horses are likely to have stronger immune systems.

A vaccine does exist for VS; however, since use of the vaccine will result in a positive antibody test, its use is regulated by government officials and is only to be used in certain situations.


VS is diagnosed by either positive antibody testing in serum samples or by virus isolation from swabs taken of lesions. VS diagnosis must be made at a federally accredited laboratory.

The virus itself, like the human cold, must run its course. Treatment is aimed at addressing the signs of the disease and preventing secondary complications. Soft feed may encourage eating.  Anti-inflammatory drugs are used to relieve pain and fever. Antibiotics may be prescribed to treat or prevent secondary bacterial infection of the VS lesions.

Premises with VS affected animals will be quarantined by the state veterinarian’s office for a specified period, usually 30 days from the time of resolution of the last case on the property.

About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.