The Colorado Department of Agriculture’s State Veterinarian’s Office has placed 69 locations under quarantine after horses and one cow tested positive for Vesicular Stomatitis (VS). The quarantines are located in Adams, Boulder, Douglas, El Paso, Larimer, and Weld counties; results on additional tests in these and other counties are pending. VS 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.

Beautiful horses
Public domain image/Dusan Bicanski

“Most confirmed cases are in horses but the risk to cattle is significant as well,” said State Veterinarian, Dr. Keith Roehr. “A cow that’s part of a herd of three head in Weld County tested positive for VS; cattle owners need to remain vigilant in their insect control efforts.”

County totals are: Adams County – 3 horses on 2 premises, Boulder County – 26 horses on 15 premises, Douglas County – 2 horses on 1 premises, El Paso County – 1 horse on 1 premises, Larimer County – 9 horses on 4 premises and Weld County – 25 horses and 1 cow on 19 premises.

For a map of Colorado counties with confirmed cases, visit

“Over the past two weeks, our office has been receiving approximately ten reports daily of animals demonstrating clinical signs that are consistent with VS. Veterinarians have been very observant and diligent to report horses and other livestock that are suspicious of being infected,” said State Veterinarian, Dr. Keith Roehr. “Livestock, including horse and cattle owners, should be aware that insect control is an important tool in the prevention of VS. Most of the cases we have investigated involve horses that have had no history of movement; therefore, controlling black flies and midges are very important in the prevention of the spread of disease.”

Veterinarians and livestock owners who suspect an animal may have VS or any other vesicular disease should immediately contact State or federal animal health authorities. Livestock with clinical signs of VS are isolated until they are healed and determined to be of no further threat for disease spread. There are no USDA approved vaccines for VS.

While rare, human cases of VS can occur, usually among those who handle infected animals. VS in humans can cause flu-like symptoms and only rarely includes lesions or blisters.

VS susceptible species include 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, teats and above the hooves of susceptible livestock. Vesicles are usually only seen early in the course of the disease. The transmission of vesicular stomatitis is not completely understood but components include insect vectors, mechanical transmission, and livestock movement.