Infected horses develop vesicles (blisters) on the muzzle, lips, tongue, ears, sheath, udder, or coronary bands. | Photo: Courtesy Dr. Ashley Salinas

After a more than three-year hiatus, vesicular stomatitis (VS) has returned to the southwestern and western United States. At the time of this writing (early August), more than 500 equine premises had been affected with VS in Colorado, New Mexico, Oklahoma, Texas, and Wyoming. We expect continued spread within those states and potentially others over the summer.

Vesicular stomatitis is a viral disease that primarily affects horses and cattle, but it occasionally affects swine, sheep, goats, llamas, and alpacas. People handling infected animals without proper biosecurity precautions can also contract the virus and experience symptoms of fever, headache, muscle aches, and severe fatigue. The virus is known to spread naturally to livestock via black flies, sand flies, and biting midges, although other insect vectors may also be involved in transmission. Clinical signs in infected horses include vesicles (blisters) on the muzzle, lips, tongue, ears, sheath, udder, or coronary bands. These vesicles rupture after a few days into crusty and oozing lesions from which the virus can further spread by direct contact. The virus can also contaminate surfaces or objects. Shared water sources, buckets and feeders, salt licks, and other objects contaminated with saliva or discharge from the lesions can lead to ongoing disease spread.

Veterinarians are required to report suspected VS to state and federal animal health officials. If they confirm the disease, they’ll place that property under state quarantine for at least 14 days from the onset of lesions in the last affected animal on the premises. This means if new animals develop lesions, the quarantine countdown restarts with each new case until no animals show clinical signs of the disease. Property owners should also practice disease mitigation strategies during the quarantine period, such as isolating lesioned animals away from others and implementing vector control measures to reduce the likelihood of continued spread