New cases of vesicular stomatitis virus (VSV) have been detected in Archuleta and La Plata counties on July 17, according to a July 20 VSV report from the U.S. Department of Agriculture’s (USDA’s) Animal and Plant Health Inspection Service.
According to the reports, each county has one new confirmed positive equine, with both counties listed as “New Affected County.”
The report notes, “Confirmed and presumptive positive premises are quarantined for at least 14 days from the onset of lesions in the last affected animal on the premises.”
The report also states, “All confirmed cases in the 2025-26 outbreak have been vesicular stomatitis New Jersey virus (VSNJV) serotype.”
It adds, “Since the start of the outbreak, 35 VSV-affected premises have been identified (27 confirmed positive, 8 presumptive positive) in 3 states, Arizona, Colorado, and New Mexico. All 35 premises have had only equine species clinically affected with 15 premises located in 6 Arizona counties (Cochise, Gila, Maricopa, Pinal, Santa Cruz, and Yavapai Counties), 4 premises located in 4 Colorado counties (Archuleta, La Plata, Montezuma, and Montrose Counties), and 16 premises located in 4 New Mexico counties (Rio Arriba, Sandoval, Santa Fe, and Valencia Counties).”
In May, when the positive case was announced in Montezuma County, the Colorado Department of Agriculture announced it is working closely with the USDA, the Colorado State University 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.
At that time, the state veterinarian advised 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, a press release at the time outlines.
It adds that 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.
More information about VSV can be found at ag.colorado.gov/VSV.
Following is additional information from the Colorado Department of Agriculture.
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 VSV outbreak. Certificates of veterinary inspection (CVIs or health certificates) issued within two to five 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. The team will provide guidance to veterinarians on appropriate sample collection and submission. Please see the updated Veterinarian Submission Guidance document on the office’s 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 the Guidelines for Fairs, Shows, Exhibitions for more information.
About VSV
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 two to eight 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.
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