Vesicular stomatitis (VS) is a viral disease that can affect many livestock species, most often in horses and cattle. The virus causes vesicles (blisters) that form primarily on the lips and tongue, around the mouth or nose, along the udder or sheath, or along the coronary bands. These virus-containing vesicles later rupture, forming erosions and ulcers. The disease is transmitted by biting flies, mainly black flies and sandflies, or biting midges.

There is no specific treatment for the disease, only supportive care until the lesions heal. The impact of the disease on the individual horse varies, depending on the location of the lesions. Severe mouth and tongue lesions can interfere with the horse eating or drinking and severe coronary band lesions can result in temporary lameness. Vesicular stomatitis is a reportable disease in the United States and affected premises are placed under quarantine to prevent disease spread.

The recent identification of VS cases in Arizona, Colorado, New Mexico, and Utah marked the start of a 2015 outbreak in the United States. This comes on the heels of a significant VS outbreak during 2014 in which a total of 435 premises in Arizona, Colorado, Nebraska, and Texas were confirmed infected; 408 of those situations involved affected equines.

The 2014 outbreak was the worst VS outbreak in the United States since 2005, and the economic impacts of the disease were felt within the equine industry at multiple levels. While the exact dollar amount for the economic loss cannot be quantified, Colorado was certainly the hardest hit and had a total of 370 VS-affected premises in 17 counties