A horse with sudden drooling, mouth blisters, coronary-band lesions, fever, reluctance to eat, or unexplained lameness is not a routine summer-skin or fly-spray problem. Vesicular stomatitis virus, commonly shortened to VSV, is active in the western United States in 2026. Riders need a clear stop-movement, isolate, and call-the-veterinarian plan.

Why VSV matters to horse owners

VSV is a contagious livestock disease that primarily affects horses and cattle. Biting flies and midges are important transmission routes. Contaminated hands, clothing, boots, buckets, tack, grooming tools, trailers, and other shared equipment can also complicate barn biosecurity.

VSV does not usually cause high mortality, but painful lesions can interfere with eating, drinking, movement, and routine care. A suspected case can trigger testing, quarantine, show disruption, interstate movement questions, and international travel restrictions.

Signs riders should check

What to do when VSV is suspected

1. Stop movement. Do not haul the horse to a show, sale, clinic, another barn, or a new pasture while the problem is being evaluated.
2. Create separation. Move the horse away from healthy horses and livestock when it can be done safely and without spreading contamination.
3. Call the veterinarian. VSV is a reportable animal disease. Your veterinarian will coordinate testing and reporting with the appropriate state and federal animal-health officials.
4. Dedicate equipment. Use separate buckets, halters, lead ropes, feed tubs, thermometers, grooming tools, and cleaning supplies.
5. Control traffic. Care for healthy horses first and the suspected horse last. Limit handlers and follow veterinary direction for gloves, clothing, footwear, cleanup, sampling, and access.
6. Start a written log. Record temperature, lesions, appetite, drinking, movement, insect pressure, recent travel, and every horse or person with possible contact.

What not to do

• Do not assume mouth sores are a bit injury, chemical irritation, summer sore, or harmless scrape without veterinary evaluation.
• Do not apply a routine topical product or fly spray into open lesions unless the current label and your veterinarian specifically support that use.
• Do not share equipment between the suspected horse and the rest of the barn.
• Do not move the horse to another facility to wait for improvement.
• Do not describe a routine fly-control product as a treatment, cure, vaccine, or guaranteed prevention for VSV.

Where routine fly control fits

Reducing biting-insect pressure is still part of sensible warm-weather barn management. Manure removal, clean pens, fly traps, physical barriers, labeled sprays on intact skin, and reducing standing water can support the broader prevention plan.

That does not make fly control a diagnosis or treatment. Use the Horse Fly Protection guide for routine planning, and follow your veterinarian and state animal-health officials when disease is suspected.

Hauling, shows, and international movement

Before hauling from or through an affected area, check current state animal-health requirements, event rules, destination-barn policies, and interstate documentation requirements. A health certificate issued before a new outbreak update may not answer every current movement question.

For Canada-bound horses, USDA APHIS currently identifies Colorado and New Mexico as VSV-affected states and states that exports of horses from VSV-affected states are suspended. Confirm current eligibility before finalizing an international trip through the USDA APHIS Canada export guidance.

If a horse has lesions, fever, unexplained drooling, or a known exposure, stop the trip and call your veterinarian. Do not let an entry deadline, hauling schedule, or one normal temperature reading overrule a disease concern.

Cleaning and barn zoning

Remove visible dirt, saliva, feed, bedding, and manure before applying a veterinarian-approved disinfectant. Organic material can reduce disinfectant performance. Follow the correct concentration and contact time, and pay attention to latches, buckets, hoses, trailer surfaces, tack, grooming tools, footwear, and vehicle touchpoints.

Keep a clean zone for healthy horses, a transition zone for supplies and clothing changes, and an isolation zone for the suspect horse. Do not carry buckets, tools, manure equipment, or clothing from isolation back into the clean barn without the required cleaning process.

Build the plan before it is needed

Keep your veterinarian's number, state animal-health contact, isolation location, dedicated buckets, disposable gloves, boot-cleaning supplies, thermometer, and a written new-arrival routine easy to find. Use the Horse Health Library and Regional Horse Care guide for broader disease, weather, travel, and emergency-readiness decisions.

Frequently asked questions