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.
If a horse develops unexplained drooling, oral blisters or erosions, lesions around the lips, nose, ears, sheath, udder, or coronary band, fever, reluctance to eat or drink, or new lameness, stop movement and call your veterinarian promptly. Separate the horse, dedicate its equipment, and follow veterinary and animal-health instructions before hauling, showing, treating lesions, or moving other animals.
As of the August 19, 2026 USDA update, 45 VSV-affected premises had been identified across Arizona, Colorado, and New Mexico: 31 confirmed positive and 14 presumptive positive. Forty-three premises had only equine species clinically affected.
The latest report added three presumptive-positive equine premises in Colorado, one in La Plata County and two in Montezuma County. One previously affected premises in La Plata County was released from quarantine. Across the outbreak, affected premises have been reported in six Arizona counties, five Colorado counties, and four New Mexico counties. Counts, counties, quarantine releases, and movement requirements can change quickly.
Check the current USDA APHIS VSV report and review current EDCC alerts before hauling or making a show decision.
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.
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.
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.
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.
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.
Yes. The August 19 USDA update reported 45 affected premises across Arizona, Colorado, and New Mexico: 31 confirmed positive and 14 presumptive positive. Check the latest official report because premises, counties, quarantine status, and movement rules can change.
Yes. Contact your veterinarian when VSV is suspected. Veterinarians and animal-health officials coordinate required testing, reporting, quarantine, and release decisions.
No routine fly spray should be presented as guaranteed VSV prevention or treatment. Insect control can reduce biting-insect pressure as one part of a broader biosecurity plan, but suspected disease requires veterinary evaluation.
Do not haul until the horse has been evaluated and you have appropriate veterinary and animal-health direction. Stop movement, separate the horse, and avoid sharing equipment.
Human infection can occur. Use careful hygiene and the personal protective measures directed by veterinary or public-health professionals when handling suspicious lesions or contaminated materials.
Last reviewed August 20, 2026. Educational information only. Diagnosis, testing, treatment, quarantine, movement, and release decisions belong with veterinarians and applicable animal-health officials. Current federal, state, event, and destination requirements supersede this page.
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