The USDA’s Animal and Plant Health Inspection Service has identified a new vesicular stomatitis (VSV)-positive equine premises in Yavapai County, Arizona.
Since October 2025, there have been 10 equine premises in Arizona and one wild horse from the Salt River Wild Horse Management Group in the Tonto National Forest that have tested positive for VSV, all of which are vesicular stomatitis New Jersey virus (VSNJV) serotype cases.
The most recent outbreak of VSV in the U.S. occurred from May 2023 to January 2024, affecting 319 premises in California, Nevada, and Texas. VSV typically circulates between livestock and insect vectors in southern Mexico and occasionally makes its way into the U.S.
EDCC Health Watch is a program by the Equine Network that uses information from the Equine Disease Communication Center (EDCC) to produce and distribute verified equine disease reports. The EDCC is a nonprofit organization funded 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 characteristic vesicular lesions such as blisters, crusts, and ulcers on various parts of the body. The virus is transmitted by biting midges and is seasonal in nature.
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 inside the ears.
- Excessive salivation due to oral lesions.
- Difficulty eating and chewing feed.
- Lameness from painful erosions on the coronary band.
- Lesions on the udder, sheath, and inside of the ear.
- Secondary infections causing slow-healing wounds.
- Increased risk for animals on pastures.
Diagnosis is based on recognizing vesicular lesions, confirmed through laboratory testing for antibodies and/or virus identification. Veterinarians must report suspected cases to state/federal animal health officials for testing.
There is no specific treatment for vesicular stomatitis. Practices include good biosecurity measures and providing pain relief, anti-inflammatories, and supportive care as advised by a veterinarian.
Isolating affected animals and placing the premises under quarantine until all horses have recovered and active lesions are gone is necessary. State Veterinarians will work with local veterinarians to implement quarantine procedures.