Vesicular Stomatitis

What is Vesicular Stomatitis? 

Vesicular stomatitis is a viral disease of horses, donkeys, mules, cattle, swine and New World camelids that occurs in the Western Hemisphere. The disease is named for the characteristic vesicular lesions it causes in the form of blisters, crusts and ulceration of the lips, muzzle, nose, tongue, ears, sheath, teats, and/or coronary band. The virus is transmitted by biting midges and therefore is seasonal.

Clinical Signs: Clinical Signs for Vesicular Stomatitis include: 

  • Vesicle formation leading to ulcerative lesions on the lips, muzzle, nostrils and tongue. The tongue is often the most severely affected area. 
  • Ulceration of the inner surface of the lips. 
  • Crusting of the muzzle, nostrils, and/or inside the ears. 
  • Excessive salivation secondary to the oral lesions. 
  • Difficulty picking up and chewing feed. 
  • Lameness due to painful erosions on the coronary band.
  • Lesions can occur on the udder, sheath and inside of the ear. 
  • Lesions can develop secondary infections resulting in slow to heal wounds. 
  • Animals on pastures are at increased risk of Vesicular Stomatitis.

Diagnosis: Initial diagnosis is based on recognition of characteristic vesicular lesions. Infection is confirmed via laboratory testing for serum antibodies and/or virus identification in fluid samples from active lesions. Veterinarians are required to report suspected VS cases to state/federal animal health officials who will direct sample submission to an approved regulatory laboratory for diagnostic testing.

Treatment: There is no specific treatment for Vesicular Stomatitis. Practicing good biosecurity and treating affected horses with pain relievers, anti-inflammatories, and supportive care as recommended by a veterinarian.

Prevention:  Isolating all affected animals and placing the premise on immediate quarantine is required until all horses have fully recovered and no active lesions are present. The State Veterinarian will work with your local veterinarian to determine and implement necessary quarantine procedures.


January 09, 2024
Sacramento County, CA
Confirmed Case(s) - Official Quarantine
December 26, 2023
Sacramento, Placer, Mariposa County, CA
Confirmed Case(s) - Official Quarantine
December 19, 2023
Mariposa, Placer, and San Joaquin Counties County, CA
Outbreak Update