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California Department of Food and Agriculture

Vesicular Stomatitis


Equine Health Alert

Recommended Biosecurity Measures for
Shows with Out of State Horses

  1. Participants, when possible, should arrive at the event with a health certificate (certificate of veterinary inspection) issued within 72 hours. California entry requirements for horses from a VSV affected state includes this statement “I have examined all the animals identified on this certificate within 14 days of shipment date and have found them to be free from signs of vesicular stomatitis virus (VSV). During the last 30 days, these animals have not been exposed to VSV nor located on a VSV confirmed or a VSV suspected premises.”
  2. At time of arrival, inspect all horses from VSV affected states for blister like lesions in the mouth (tongue, lips), the nostrils, around the coronary band of the hooves, inner or outer ear.
  3. Immediately quarantine any horse with vesicular lesions and contact your local California Department of Food and Agriculture Animal Health Branch Office.
  4. Stable all horses from a VSV affected state in a separate stabling area.
  5. Eliminate breeding grounds for vectors specifically, the black fly, by daily removal of manure and elimination of standing water.
  6. Utilize fly wipes, sprays, foggers and other repellents for use on animals and premises should be applied as directed by label instructions. Encourage use of pyrethrin fly spray labelled for horses especially during peak black fly mid-morning and at dusk in the evening.
  7. Require exhibitors, owners and trainers to report any suspicious lesions to the show veterinarian or show secretary office immediately.
  8. Utilize disinfectant to disinfect communal areas and equipment. Effective disinfectants include 2% sodium carbonate, 4% sodium hydroxide, 2% iodophore disinfectants, chlorine dioxide disinfectants, ether and other organic solvents, and 1% formalin.
  9. Event organizers should regularly observe all susceptible livestock on event grounds for clinical signs of VS during an event. Often, excess salivation is often the first sign of disease.
  10. At the end of the event, obtain destination information on all horses and email contact information for the person responsible for the care of the horse to ensure they can be contacted and provided guidance if a disease outbreak occurs.


Vesicular stomatitis virus (VSV) is a viral disease agent that affects primarily horses and cattle and occasionally swine, sheep, goats, llamas and alpacas. Humans that handle affected animals may become infected, but this is a rare event.

Outbreaks usually occur during the warm summer months, particularly in animals pastured along waterways.

Although VSV does not usually cause animals to die it does cause significant economic losses to livestock producers. In addition, the disease is of particular concern because its outward clinical signs are similar to Foot and Mouth Disease (FMD), a foreign animal disease eradicated from the United States (U.S.) in 1929. VSV cannot be diagnosed on clinical signs alone; sampling and laboratory testing is crucial to diagnose the vesicular condition and to differentiate it from other diseases, such as FMD or swine vesicular disease.

Clinical Signs

Livestock infected with VSV usually show clinical signs 2-8 days after exposure to the virus. The first sign is usually excessive salivation due to vesicles, blister-like lesions, in the mouth. Vesicles may also be found on the nostrils, teats, and around the hooves. Vesicles swell and break, exposing raw tissue, causing pain and discomfort. Animals may refuse to eat or drink and may show signs of lameness. Affected animals usually recover within two weeks.

Disease Spread

The exact mechanism of spread is currently unknown, but biting insects and animal-to-animal contact may play a role in the spread of the disease. An infected animal’s salvia and fluid from ruptured vesicles can contaminate feed, water, housing and other objects, further spreading the disease.

Diagnosis & Prevention

There is no specific treatment or cure for animals infected with VSV and there are no vaccines available to prevent this disease. Veterinarians and livestock owners who suspect an animal may have VSV or any other vesicular disease should immediately contact a State or Federal animal health authority.

Testing for VSV antibodies in serum (blood) samples, and/or detection of VS virus from swabs of lesions, blister fluid and tissue samples can confirm VSV viral infections.

Even with the best defense measures, VSV can still affect your herd. The following are ways to help protect horses and livestock:

  • Limit movement of animals from affected premises
  • Apply insect control programs
  • Separate animals with lesions from healthy animals
  • Bring animals indoors at night to reduce their exposure to biting insects, and
  • Use individual animal equipment or disinfect equipment between animals

California Movement Restrictions


Based on the international delisting of VSV as a reportable disease and recent scientific evidence, California has revised the VSV entry requirement statement required on Certificates of Veterinary Inspection (CVI/health certificate) from VSV affected states.

Currently, all horses, cattle, swine, sheep, and goats from a state where VSV has been diagnosed, or visiting an infected state and then returning to California, except those moving directly to slaughter, must be accompanied by a CVI that includes the statement:

“I have examined all the animals identified on this certificate within 14 days of shipment date and have found them to be free from signs of vesicular stomatitis virus (VSV). During the last 30 days, these animals have not been exposed to VSV nor located on a VSV confirmed or a VSV suspected premises.”