Horse owners in Colorado should remain vigilant as two new equine premises have been confirmed positive for Vesicular Stomatitis (VSV), expanding the state’s list of affected counties.

According to the USDA Animal and Plant Health Inspection Service (APHIS) and the Equine Disease Communication Center (EDCC), the newly confirmed cases are located in Archuleta County and La Plata County. Both facilities have been placed under quarantine to help prevent further spread of the disease.

The new cases mark the first confirmed VSV-positive premises in both counties during the current outbreak.

Current Colorado Situation

The latest update shows that Colorado now has confirmed affected equine premises in four counties:

• Archuleta County (newly affected)
• La Plata County (newly affected)
• Montezuma County
• Montrose County

There is also encouraging news. Since the previous USDA situation report, one previously affected premises in Montrose County has been released from quarantine after meeting the requirements for recovery.

Regional Outbreak Continues

The current outbreak extends beyond Colorado into neighboring states.

According to the USDA, 35 affected equine premises have been identified since the outbreak began across:

• Arizona
• Colorado
• New Mexico

Of those premises:

• 27 have been laboratory-confirmed
• 8 remain presumptive positive

To date, only equine species have been clinically affected, and all confirmed cases have been identified as the Vesicular Stomatitis New Jersey Virus (VSNJV) serotype.

The EDCC also reports that one new presumptive positive equine premises has been quarantined in Valencia County, New Mexico, while another previously affected premises in Rio Arriba County has been released from quarantine.

What Is Vesicular Stomatitis?

Vesicular Stomatitis is a viral disease that affects horses, donkeys, mules, cattle, swine, and camelids throughout the Western Hemisphere.

The disease causes painful blister-like lesions that eventually rupture, leaving ulcers and crusting. While most horses recover with supportive care, the lesions can be uncomfortable, interfere with eating, and occasionally become secondarily infected.

Unlike many equine diseases spread directly between horses, VSV is primarily transmitted by biting insects, particularly biting midges and black flies, making it a seasonal concern during warmer months.

Clinical Signs Horse Owners Should Watch For

Signs of Vesicular Stomatitis may include:

• Blisters or ulcers on the lips, tongue, muzzle, or nostrils
• Crusting around the nose or inside the ears
• Excessive drooling
• Difficulty eating or chewing
• Painful lesions around the coronary bands that may cause lameness
• Lesions on the sheath or udder
• Slow-healing wounds if lesions become infected

Because the lesions can resemble those caused by other reportable foreign animal diseases, any horse showing suspicious signs should be examined by a veterinarian promptly.

Diagnosis and Quarantine

Veterinarians diagnose suspected cases based on clinical signs, but laboratory testing is required to confirm infection.

Suspected cases must be reported to state and federal animal health officials, who coordinate testing through approved diagnostic laboratories.

Once a case is confirmed, the affected premises is placed under quarantine until:

• All affected horses have recovered
• Active lesions have healed
• State animal health officials determine quarantine requirements have been met

There Is No Specific Cure

There is currently no antiviral treatment specifically approved for Vesicular Stomatitis.

Veterinary care focuses on:

• Pain management
• Anti-inflammatory medications
• Supportive care
• Preventing secondary infections
• Maintaining hydration and nutrition

Most horses recover with appropriate veterinary care, although healing can take several weeks depending on the severity of the lesions.

Protecting Your Horses

While no prevention strategy eliminates all risk, horse owners can reduce exposure by:

• Using fly control measures around horses and barns
• Eliminating standing water where insects breed
• Cleaning and disinfecting shared equipment
• Avoiding unnecessary horse movement into affected areas
• Monitoring horses daily for oral lesions or excessive drooling
• Contacting a veterinarian immediately if suspicious lesions develop

As Colorado enters peak insect season, remaining alert for early signs of disease and practicing good biosecurity can help reduce the risk of additional spread.

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Source: The outbreak information in this article is based on the latest updates from the USDA Animal and Plant Health Inspection Service (APHIS) and the Equine Disease Communication Center (EDCC). For the complete national situation report and the latest updates, visit the USDA’s Vesicular Stomatitis information page.