Colorado State Study Shows Controlling Insects Can Reduce Risk of Vesicular Stomatitis Outbreaks

Note to Editors: Note to media: High resolution photos displaying symptoms of vesicular stomatitis are available at with the post of this release.

Preliminary results from a study conducted by Colorado State University’s Animal Population Health Institute indicates that controlling insects around horses and livestock may reduce the likelihood of vesicular stomatitis, a painful disease caused by a virus. Scientists have suspected that one primary source of the spread of the disease is through insects; however, not all details about how the disease spreads have been determined. This research shows evidence that horse and livestock owners can help curb the spread of the virus in localized areas.

     Vesicular stomatitis causes painful blisters and sores on infected animals, such as in their mouths, and on their tongues and skin around their hooves. While vesicular stomatitis is rarely fatal to animals, it has a substantial economic impact on the livestock, horse and agricultural industries because of restrictions on areas experiencing outbreaks of the disease. For example, once the disease has been detected in a state or geographical area, the movement of horses and livestock within, into and out of that area is restricted.

While scientists are still researching details of how the virus spreads, it is believed that it can be carried and transmitted by insect vectors and from animal-to-animal contact. One type of vesicular stomatitis virus is spread by phlebotomine sandflies. Once introduced, the disease can be spread from animal to animal by contact or exposure to saliva or fluid from ruptured lesions.

The Colorado State finding is consistent with prior research suggesting that insects may play a role in the disease transmission and suggests that livestock owners may reduce the likelihood of the disease developing in their herds by controlling insect populations. The most frequent insect control measures used by premises that participated in the study included spraying the premises, animals or both with insect control products.

"This study was in response to the 2004 outbreak of vesicular stomatitis that infected animals on 294 premises in 43 counties in Texas, New Mexico and Colorado," said Dr. Paulo Duarte, assistant professor and veterinarian in the Animal Health Population Institute. "This year, a new, ongoing outbreak of the disease has already infected animals in Texas, New Mexico, Colorado, Arizona, Wyoming, Utah and Montana, causing economic losses and animal suffering."

The Animal Population Health Institute collaborated with the U.S. Department of Agriculture’s Veterinary Services and with state veterinary offices in Colorado, Texas and New Mexico to conduct this study. The study also involved Colorado State honors veterinary students, who played an integral role by helping develop research materials and survey livestock owners to gather information.

Vesicular stomatitis primarily affects horses, cattle and swine, but also is occasionally diagnosed in sheep, goats, llamas and alpacas. Although rare, humans can contract the disease. Vesicular stomatitis has been confirmed only in the Western Hemisphere and it is known to be endemic in the warmer regions of North, Central and South America. However, outbreaks of the disease in temperate regions might occur sporadically.

The most common clinical signs of vesicular stomatitis are blisters and ulcers in the mouth, lips and muzzle, and, as a consequence, the animal salivates excessively and has difficulty eating. Blisters and ulcers also can occur on the skin near the hoof and on teats of female animals.

Vesicular stomatitis is a reportable disease in every state in the United States. For additional information about vesicular stomatitis, visit