My family and I went to the Larimer County Fair last weekend. The carnival rides were a big hit (as usual), but I always make a point of dragging the kids through the livestock pavilions. This is one of the few instances I can easily introduce them to the world of cattle, sheep, pigs, chickens, and the like.


Seeing all the horses at the fair was anxiety-inducing rather than fun for me, however. This area is in the middle of a bad outbreak of vesicular stomatitis (VS), and I worried that bringing all those gorgeous creatures together for a long weekend of fun might be putting their health at risk. Even though I was at the fair simply as a spectator, the vet in me couldn’t stop checking to see if any of the horses seemed to be drooling excessively, which is one of the early signs of the disease.


Vesicular stomatitis is caused by a viral infection. Cattle, horses, and pigs are the most common victims, but sheep, goats, llamas, and alpacas can also be affected. This year’s Colorado outbreak has been affecting horses almost exclusively. At last count 201 horses and 3 cows have tested positive for VS.


Animals can become infected with VS through direct contact with individuals shedding the virus, through contaminated equipment, or via flying insects that carry the virus from one animal to another. The disease causes blister-like lesions to develop in and around the mouth, nose, and hooves, and oftentimes on the teats of lactating females (e.g., dairy cows). The blisters rupture, leaving behind raw sores that are so painful affected animals are reluctant to eat, drink, and move around. People who come in contact with VS infected animals can develop flu-like symptoms, but human cases are quite rare.


Vesicular stomatitis is rarely fatal. Most animals recover in about two weeks unless secondary infections set in, but it is still very important for two main reasons:


1. VS can lead to significant economic losses due to weight loss, drops in production (e.g., milk in dairy cows), performance declines, and the quarantines necessary to control the disease.


2. In cloven-hooved animals (e.g., cattle, pigs, sheep, goats), VS lesions look a lot like those associated with foot and mouth disease, a more severe viral infection that has been eradicated from the United States. Therefore, all infections that cause vesicular (blister-like) lesions in livestock must be reported to appropriate governmental agencies.


Colorado State Veterinarian Dr. Keith Roehr says “Over the past two weeks, our office has been receiving approximately ten reports daily of animals demonstrating clinical signs that are consistent with VS. 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.”



So far I haven’t heard of any cases associated with horses travelling to the Larimer County Fair. Fingers crossed it stays that way.


Dr. Jennifer Coates


Image: Rita Kochmarjova / Shutterstock