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Animal and Plant Health Inspection Service
U.S. Department of Agriculture
USDA FAQ's and resources about coronavirus (COVID-19).  LEARN MORE

Vesicular Stomatitis (VS)

Vesicular stomatitis (VS) is a viral disease that primarily affects horses and cattle and occasionally swine, sheep, goats, llamas, and alpacas.  Humans can also become infected with the disease when handling affected animals, but this is a rare event.  Vesicular stomatitis has been confirmed only in the Western Hemisphere.  It is known to be an endemic disease in the warmer regions of North, Central, and South America, and outbreaks of the disease in other temperate geographic parts of the hemisphere occur sporadically. The Southwestern and Western United States have experienced a number of vesicular stomatitis outbreaks, the most recent and largest VS outbreak occurred in 2015.  Outbreaks usually occur during the warmer months, often along waterways.  The time from exposure to the onset of clinical signs is 2-8 days. VS is a state reportable disease.

If you suspect vesicular stomatitis, contact your local State Animal Health Official.

Collect swabs of the lesions and serum to be sent to the National Veterinary Services Laboratories (NVSL) for confirmation of an index case.  In the event of an outbreak, your local NAHLN laboratory may become approved to test equine samples after the index case in your state is confirmed.   

Set up a quarantine for the farm to help prevent spread of the disease. Ensure good biosecurity practices when handling sick and healthy horses. Use and advise your clients to use personal protective equipment when handling lesioned animals to prevent zoonotic transmission.
  • Blister-like lesions in/around mouth, nose, coronary band, and/or sheath/udders
  • Fever
  • Drooling/frothing at mouth
  • Reluctance to eat
  • Lameness or laminitis if lesions develop around coronary band
  1. Call your veterinarian immediately.
  2. Separate affected horse(s) from all healthy horses on the property.
  3. Controlling insects (fly spray, fly traps, maintaining clean pens, etc.) is essential to reducing the risk and the spread of this disease.
  4. Handle all healthy animals before sick animals. After handling sick animals make sure to wash and disinfect your hands and boots, if possible change and wash your clothes as well.
Vesicular stomatitis is treated with supportive care. Since the lesions may be quite painful your veterinarian may prescribe anti-inflammatory drugs. If your horse is having trouble eating, softening their grain in warm water could encourage higher consumption. Softening hay cubes can also help if they are having trouble eating grass/hay. Secondary infections may develop at erosion sites and systemic antibiotic therapy may be warranted.
Practice good biosecurity and isolate new horses when introduced to the herd. Keeping insect population down may also help in the prevention of VS. There have been experimental vaccines developed but none have been approved for use in horses.
VS is spread by insect vectors and direct contact with infected animals. Black flies, sand flies, and midges are the known vectors of this disease, but other insects may also be capable of transmission. Infected animals shed the virus from the lesions (blisters) they develop, so direct contact with infected animals or water, feed, buckets, and other fomites contaminated with saliva from infected animals can also transmit the disease. The virus can also be spread on shoes, clothing, hands, and contaminated equipment.
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