The USDA’s Animal and Plant Health Inspection Service has reported two new vesicular stomatitis (VSV)-positive equine premises in Yavapai County, Arizona.
Furthermore, four previously affected premises have been released from quarantine since March, including one in Gila County, one in Maricopa County, and two in Yavapai County.
Since October 2025, VSV has been found at 13 equine premises in Arizona, as well as in a wild horse from the Salt River Wild Horse Management Group in the Tonto National Forest. All confirmed cases have been of the vesicular stomatitis New Jersey virus (VSNJV) serotype.
The most recent outbreak of VSV in the U.S. occurred from May 2023 to January 2024, affecting 319 premises across California, Nevada, and Texas. VSV typically circulates between livestock and insect vectors in southern Mexico and only occasionally crosses into the U.S.
EDCC Health Watch is an Equine Network marketing program that uses information from the Equine Disease Communication Center (EDCC) to create and distribute verified equine disease reports. The EDCC is an independent nonprofit organization supported by industry donations to provide open access to infectious disease information.
About Vesicular Stomatitis
Vesicular stomatitis is a viral disease that affects horses, donkeys, mules, cattle, swine, and New World camelids in the Western Hemisphere. It causes vesicular lesions such as blisters, crusts, and ulceration on various parts of the body. The virus is transmitted by biting midges and is seasonal in nature.
Common clinical signs of vesicular stomatitis include:
- Vesicle formation leading to ulcerative lesions on the lips, muzzle, nostrils, and tongue.
- Ulceration of the inner surface of the lips.
- Crusting of the muzzle, nostrils, and ears.
- Excessive salivation due to oral lesions.
- Difficulty picking up and chewing feed.
- Lameness from erosions on the coronary band.
- Lesions on the udder, sheath, and inside of the ear.
- Development of secondary infections in lesions.
- Increased risk for animals on pastures.
Diagnosis is based on recognizing vesicular lesions, with confirmation through laboratory testing for serum antibodies and virus identification in fluid samples. Veterinarians must report suspected cases to state/federal animal health officials for testing at approved laboratories.
There is no specific treatment for vesicular stomatitis. Practices include implementing biosecurity measures and providing pain relief, anti-inflammatories, and supportive care as advised by a veterinarian.
Isolating affected animals and placing the premise under immediate quarantine is necessary until all horses have fully recovered with no active lesions. The State Veterinarian will work with local veterinarians to determine and enforce quarantine procedures.