Colorado confirms first vesicular stomatitis premises of 2026

Colorado has confirmed its first vesicular stomatitis virus, or VSV, affected premises of 2026, with USDA’s National Veterinary Services Laboratories confirming infection on May 7 in Montezuma County. The case involves one horse on a five-horse premises, and the animal tested positive for vesicular stomatitis New Jersey virus by both PCR on lesion swabs and cELISA on serology. This is Colorado’s index case for 2026 and extends the 2025-26 outbreak that began in Arizona in October 2025. As of USDA’s May 7 situation report, the outbreak has involved 16 confirmed premises across Arizona and Colorado, all with clinically affected equine species. (aphis.usda.gov)

Why it matters: For veterinarians, the confirmation changes Colorado’s status from watchful surveillance to active response. The Colorado Department of Agriculture says that before an index case is confirmed, all suspected cases must be reported and evaluated by state or federal animal health officials; once a county is confirmed VSV-positive, APHIS guidance allows additional equine premises in that county with compatible clinical signs to be quarantined as presumptive positives without requiring confirmatory testing. Quarantines last at least 14 days from lesion onset in the last affected animal, and movement restrictions can ripple into interstate transport, event participation, and certificate of veterinary inspection planning. VSV is also zoonotic, though human infection is rare, so clinic and farm biosecurity matter. (ag.colorado.gov)

What to watch: Watch for any additional quarantined premises in Montezuma County or nearby counties, plus whether Colorado issues added movement guidance as insect activity increases into late spring and summer. (aphis.usda.gov)