Vesicular Stomatitis Virus



The last detection of Vesicular Stomatitis Virus was in White Pine County on July 28, 2023. The affected premises was placed under quarantine, and the quarantine was lifted on Aug. 8, 2023. 

What is Vesicular Stomatitis Virus?

Vesicular stomatitis virus (VSV) is a viral disease 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 an uncommon occurrence.
VSV is most commonly spread through biting flies and mosquitos, and animal-to-animal contact. Outbreaks usually occur during the warm summer months, particularly in animals pastured along waterways, but can occur anytime there is an influx and/or migration in the fly vector populations.

Although VSV does not usually cause animal deaths, it can 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 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 play a large role in the spread of the disease. An infected animal’s saliva and fluid from ruptured vesicles can contaminate feed, water, housing and other objects, further spreading the disease.

Diagnosis and 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 VSV from swabs of lesions, blister fluid and tissue samples can confirm VSV viral infections. VSV diagnostic testing can only be performed by a state or federal veterinarian or USDA Accredited Veterinarian.

It is important to protect animals with proper and diligent biosecurity measures. The following is an overview of 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 use on each animal.

Recommended biosecurity measures for equine events during a VSV outbreak in Nevada
  1. Participants, whenever possible, should arrive at the event with a certificate of veterinary inspection (CVI) issued within 2-5 days prior to the event. CVIs should include this statement: “I have examined all the animals identified on this certificate within 7 days of the shipment date and have found them to be free from signs of vesicular stomatitis virus (VSV). During the last 14 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 and prior to entry onto the event grounds, all horses should be inspected by a USDA Category II Accredited Veterinarian for blister-like lesions in the mouth (tongue, lips), the nostrils, around the coronary band of the hooves, around the teats, and inner or outer ear.
  3. Immediately quarantine any horse with vesicular lesions and contact the Nevada Department of Agriculture State Veterinarian at diseasereporting@agri.nv.gov.
  4. Stable all horses from a known VSV-affected county in a separate stabling area.
  5. Horses from known VSV-affected counties should be observed daily for vesicular lesions and checked for elevated temperatures twice daily with documentation.
  6. Eliminate breeding grounds for VSV transmission vectors, specifically, the black fly, by daily removal of manure and elimination of standing water.
  7. Avoid use of communal water sources to the best extent possible. Every animal should have its own water bucket/receptacle, and communal hoses should never be in direct contact with the buckets/receptacles themselves.
  8. Utilize fly wipes, sprays, foggers and other repellents for use on animals and premises as directed by label instructions as frequently as indicated. Encourage use of pyrethrin fly spray labelled for horses, especially during peak black fly exposure: mid-morning and at dusk in the evening.
  9. Require exhibitors, owners and trainers to report any suspicious lesions to the show veterinarian or contact the secretary office immediately.
  10. 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.
  11. Event veterinarians AND event management should regularly observe all susceptible livestock (equids, cattle, sheep, goats, pigs, llamas, alpacas, camels) on event grounds for clinical signs of VSV during an event. Often, excess salivation is the first sign of disease. Any VSV suspects should be immediately isolated.
  12. At the end of the event, obtain destination information for all departing horses, as well as email contact information for the person responsible for the care of the horse(s) to ensure they can be contacted and receive guidance if a disease detection occurs.
  13. Equine events without a veterinarian in attendance and inspection of all horses prior to entry into the equine event facility are not recommended during a VSV outbreak and should be held only at the risk and discretion of event management.

Click here for VSV guidelines for shows and fairs


Interstate and international movement restrictions

Receiving states and countries often impose additional requirements or restrictions for susceptible animals originating from VSV-affected states. Verify all entry requirements with the destination state or country PRIOR to any out-of-state movement. A shortened inspection period (often 7 days but occasionally as short as 24 hours) is usually required in addition to a specific inspection statement from the inspecting veterinarian as dictated by the receiving state or country.


    Equine Infectious Anemia

    Equine infectious Anemia (EIA) is a viral disease transmitted through blood contact in equine species, including horses, donkeys and mules, that can cause fever, weakness, swelling, irregular heartbeat and low red blood cell count. Common sources of transmission are blood-feeding insects such as flies, or with the reuse of infected needles and other contaminated medical, dental or tattoo equipment. It cannot be spread through coughs, sneezes or casual contact. It cannot be transmitted to humans and is not a public health risk.

    Horses suspected to be ill should be reported to their veterinarian for appropriate care. Infected horses may not show symptoms but remain carriers for life, making routine testing key to prevention of spread of this disease. This is a reportable disease, meaning when veterinarians diagnose it, they are required to notify the NDA, per NRS 571.160. The NDA website includes a list of reportable diseases.

    There is no known treatment for EIA. Infected horses are lifelong carriers of the virus and can potentially infect other horses. Routine testing is important to preventing the potential spread of disease. Management choices for EIA positive horses include either euthanasia or lifelong quarantine with permanent isolation that includes being at least 200 yards from any other horses.

    Prevention and control of EIA

    Horse owners are urged to practice good horse health safety measures to reduce chances of an infectious disease being transferred, and get as much background information as possible before purchasing horses. Basic practices include:

    • Single-use medical equipment such as needles, syringes, and IV lines should never be re-used, and should never be shared between different horses. Dental tools and other instruments should be fully sterilized between horses.
    • Practice good fly control by keeping stalls dry, removing standing water, managing manure, and using fly deterrents and repellants.
    • Horses should have a routine testing schedule for EIA and should be tested prior to attending events.
    • Test horses at the time of purchase examination. Work with a veterinarian on a quarantine and/or retesting protocol prior to introducing a new horse to current horses. Before purchasing, get as much background information on the horse including any domestic or international travel or importation.
    • Any horses entering the U.S. from other countries require testing and quarantine prior to entry.

    Equine species are required to have a Certificate of Veterinary Inspection and a negative EIA (Coggin’s) test within 12 months prior to entry as part of Nevada's entry requirements. Negative EIA tests are required for movement between all states and the U.S. Department of Agriculture lists EIA requirements for importation into the U.S.


    As of Aug. 3, 2022, a detection of EIA was confirmed in a horse at a facility in Clark County during routine testing. A quarantine has been issued for the facility and all horses on the premises will undergo testing to prevent potential spread of the disease.

    Horses that attended an event in Washoe County within the month of June 2022 are also encouraged to test.

    View the Equine Infectious Anemia Quarantine FAQ for additional information. 

    Resources and helpful links

    Equine Herpes Virus (EHV)