Horses on two Montrose County and one Delta County premises have tested positive for vesicular stomatitis (VS) and have been placed under quarantine, the Colorado Department of Agriculture (CDA) reported July 2.

Colorado has become the fourth state in the country to have confirmed equine VS cases in 2015. Previous positive cases of vesicular stomatitis this year have been diagnosed in Arizona, New Mexico, and Texas.

On July 2, the National Veterinary Services Laboratory reported positive tests. The initial Colorado disease investigations were accomplished by field veterinarians from the state veterinarian’s office at the Colorado Department of Agriculture.

“The primary spread of VS is thought to occur through insect vectors; the horses involved in these cases have no history of travel,” said State Veterinarian Keith Roehr, DVM. “Vesicular stomatitis can be painful for animals and costly to their owners. The virus typically causes oral blisters and sores that can be painful causing difficulty in eating and drinking.”

A 2014 VS outbreak resulted in 556 livestock investigations in Colorado and 370 quarantines. The final quarantines were released in January 2015.

A number of species are susceptible to VS, including horses, mules, cattle, bison, sheep, goats, pigs, and camelids. The clinical signs of the disease include vesicles, erosions, and sloughing of the skin on the muzzle, tongue, and teats and above the hooves of susceptible livestock. Vesicles are usually only seen early in the course of the disease.

Disease transmission is not completely understood, but components include insect vectors,