VSV Case Confirmed in Colorado Equine

The Colorado State Veterinarian's Office has confirmed a detection of vesicular stomatitis virus (VSV) in a horse in Montezuma County, with two additional horses showing clinical signs. The case was confirmed by the USDA's National Veterinary Services Laboratories on May 7, and the premises with the infected horse has been placed under quarantine. The virus was most likely spread by biting insects, such as flies or midges.

"Equine and livestock owners should monitor their animals for blisters and report any suspected cases to their veterinarian, who will then coordinate with our office for testing and follow-up," said Dr. Maggie Baldwin, Colorado State Veterinarian. "Having an index case in Colorado also may impact interstate and international movement of equine and livestock. Please contact your veterinarian to ensure you meet the most up-to-date movement requirements."

CDA is working closely with the U.S. Department of Agriculture (USDA), the CSU Veterinary Diagnostic Laboratory, and the Colorado Department of Public Health and Environment to respond to this detection and protect the health of both people and animals.

The Montezuma County premises is being monitored and will remain under state quarantine until at least 14 days from the onset of lesions in the last affected animal on the premises. While the current risk to Colorado's equine and livestock population is low, the State Veterinarian is advising owners to be on the lookout for any signs of the disease.

One way owners can protect their animals from the virus is by using insect control programs and avoiding contact with animals from other farms. Any new horses or livestock should be quarantined before being introduced to the herd.

Owners who notice any signs of disease should separate sick animals and report it immediately to their veterinarian. Owners should wear proper protective equipment such as gloves any time they are working with sick animals and should wash and disinfect their hands and boots after contact. While it is rare, VSV can be transmitted to people and can cause a flu-like illness and rarely blister-like sores. Currently, there are no human cases, and the risk to the general public is very low.

More information about VSV can be found at ag.colorado.gov/VSV.

Tips for livestock owners

Strict fly control is an important factor to inhibit the transmission of the disease.

Avoid transferring feeding equipment, cleaning tools or health care equipment from other herds.

When moving livestock interstate, Colorado veterinarians and livestock owners should contact the Animal Health Officials in the destination state to ensure all import requirements are met.

Colorado fairs, livestock exhibitions, and rodeos may institute new entry requirements based on the extent and severity of the current VS outbreak. Certificates of veterinary inspection (CVIs or health certificates) issued within 2-5 days prior to an event can be beneficial in reducing risks.

Important Information for Veterinarians

Any vesicular disease of livestock is reportable to the State Veterinarian's Office in Colorado - to report call 303-869-9130. After hours, the voice message will indicate which staff veterinarian is on call. Our team will provide guidance to veterinarians on appropriate sample collection and submission. Please see the updated Veterinarian Submission Guidance document on our website.

All suspected VSV in non-equine cases (cattle, sheep, goats, pigs, camelids) must be investigated by state or federal animal health officials.

Information for Shows and Fairs

The Colorado State Veterinarian's Office recommends that livestock event organizers consider extra precautionary measures for both participants and the event venue to minimize the risk of transmission of VSV. See these Guidelines for Fairs, Shows, Exhibitions for more information.

About Vesicular Stomatitis

This viral disease primarily affects horses and cattle, and occasionally swine, sheep, goats, llamas, and alpacas. The disease can be transmitted by insects such as black flies, sand flies, and biting midges or through direct contact with infected animals or contaminated objects. The incubation period ranges from 2-8 days. Clinical signs include blister-like sores on the mouths and feet of infected animals and appear similar to foot and mouth disease. Often excessive salivation is the first sign of disease, along with a reluctance to eat or drink. Lameness and weight loss may follow. There are no USDA-approved vaccines for VSV.

Some species of wildlife (e.g., deer and elk) may be susceptible to VSV. If you encounter a sick or deceased wild animal or have other wildlife-related questions, please contact your local Colorado Parks and Wildlife Office.

Humans may become infected when handling affected animals or contaminated fomites, but this is a rare event. To avoid human exposure, individuals should use personal protective measures when handling affected animals. Any symptomatic animal owners of affected premises should seek care and notify their healthcare provider of exposure to VSV.

While it is early in the year for Colorado to have its first detection of VSV, it is not entirely unexpected as Arizona has had a handful of cases of VSV since October 2025. The last VSV outbreak in Colorado occurred in 2019, with nearly 700 affected premises in 38 counties (USDA Situation Report).