Vesicular Stomatitis in Horses: Signs, Quarantine and Colorado Cases

What's happening with vesicular stomatitis in horses in Colorado

Vesicular stomatitis in horses is a reportable viral disease that causes painful blisters and sores on the mouth, muzzle, ears, sheath and coronary band, and two more Colorado horse properties are now under quarantine for it. USDA APHIS's Sept. 18, 2026 situation report added one presumptive-positive equine premises in Delta County and one in Montezuma County.

The Equine Disease Communication Center (EDCC) Health Watch shared the news on Sept. 21. As of APHIS's report, three Colorado premises were under quarantine, while two older Colorado premises in La Plata and Montezuma counties had just been released.

Why "presumptive" matters

These new cases are presumptive, not lab-confirmed. Under APHIS rules, once a county already has a confirmed VSV case, new horses there with typical signs can be quarantined and counted as presumptive positive without more testing.

So treat these as strong suspicion backed by clinical signs. It's the right call for control, but it's not the same as a lab result.

The bigger 2025-26 picture

This outbreak started on Oct. 31, 2025, when the national lab confirmed VSV in Cochise County, Arizona. Colorado's first case was confirmed May 7, 2026, in Montezuma County, and New Mexico followed on May 22.

In total, APHIS counts 49 affected premises (32 confirmed, 17 presumptive). Horses were the only species with signs on 46 of them, and cattle on the other 3. Every confirmed case has been the New Jersey serotype (VSNJV).

What is VSV?

Vesicular stomatitis virus (VSV) infects horses, donkeys, mules and cattle. Camelids such as llamas and alpacas, pigs, sheep and goats can also catch it.

It spreads two main ways:

• Biting insects. Black flies, sand flies and biting midges (Culicoides, often called no-see-ums) carry the virus. That's why cases cluster in warm months and stop after hard freezes.
• Direct contact. Saliva and fluid from broken blisters carry virus. Shared bits, buckets, water troughs, feed tubs and tack can move it from horse to horse.

The virus is endemic from southern Mexico through Central America to northern South America. It only moves north into the U.S. in some years, when weather helps infected insects travel. Signs usually show up 2-8 days after infection, according to Colorado State University's vet hospital.

Vesicular stomatitis symptoms: what to look for

The first thing many owners notice is drooling or a horse that walks up to the feed tub and then won't eat. Look closer and you may find:

• Blanched (pale) raised spots or blisters on the tongue, gums or lips
• Raw ulcers where blisters have burst, sometimes large patches on the tongue
• Crusty scabs on the muzzle, lips, ears, sheath or belly
• Sores at the coronary band (where the hoof meets the hair), which can make a horse lame
• A short fever early on, which may be gone by the time you notice sores

Blisters break quickly, so you may only see crusts or raw spots. Some horses have mild signs that are easy to miss, which is why a daily look at the lips and muzzle during grooming pays off.

How long does it last?

Most horses recover in about two weeks, and deaths are rare. The real costs are weight loss from not eating, hoof problems when the coronary band is involved, and weeks of lost travel under quarantine.

Why VSV is reportable (and what quarantine means)

VSV looks almost exactly like foot-and-mouth disease (FMD) in cattle and pigs. FMD is a foreign animal disease the U.S. works hard to keep out, so every blister case in livestock needs testing or official review to rule it out.

That's why your vet must report suspected VSV to state and federal animal-health officials. It's not a punishment, and it protects every barn around you.

Here's how quarantine works:

1. Your vet examines the horse and reports it to the state veterinarian.
2. Officials may sample the lesions or, in an already-confirmed county, classify the property as presumptive positive.
3. All susceptible animals on the property are quarantined, not just the sick horse.
4. Quarantine lasts at least 14 days from when the last affected animal's lesions started.
5. Officials release the property when no new cases appear.

During quarantine, no horses leave for shows, trail rides, sales or clinics. Isolate sick animals, step up insect control and keep separate equipment for them.

Is it contagious to people?

Yes, occasionally. People who handle infected horses can get a short flu-like illness with fever, headache and muscle aches, and sometimes blisters in the mouth or on the lips or hands.

Wear gloves when you check or handle a horse's mouth sores. Wash your hands afterward and keep saliva and blister fluid away from your eyes, mouth and any cuts.

Treatment: supportive care from your vet

There's no drug that kills the virus, and there's no VSV vaccine for horses in the U.S. Some Latin American countries use VSV vaccines in cattle and pigs, but Colombia's animal-health agency (ICA) doesn't recommend them for horses because the vaccine can cause granulomas (lumps) at the injection site. Your vet's job is to keep the horse comfortable, eating and drinking while the sores heal.

Supportive care may include pain relief, soft, easy-to-chew feeds, gentle mouth care and treatment for secondary infections. Your vet decides what's right for your horse; don't start medications on your own.

VSV horse show travel rules and your fall checklist

Fall is prime show and trail season in the Rockies and Southwest, and insects keep biting until the first hard freezes. Many shows and states tighten rules while VSV is active.

What organizers and states may require

• A Certificate of Veterinary Inspection (CVI) issued within a shorter-than-usual window before arrival
• A vet's statement on the CVI that the horse was examined and is free of VSV signs
• Proof the horse hasn't been on or near a VSV-quarantined premises recently
• In some cases, no entries from affected counties at all
• A current negative Coggins test, which is required for most interstate travel anyway

Rules change quickly during an outbreak. Call the destination state's animal-health office or check its website a few days before you haul, and read your show's entry packet closely.

Fall travel and show checklist

• Insect control: Use fly sprays labeled for horses, fly masks with ear covers and fly sheets. Bring horses in at dusk and dawn, when biting midges are busiest.
• Clean up breeding spots: Drain standing water and manage manure around the barn.
• Don't share: Bring your own bits, buckets, hay nets, sponges and tack. Skip communal water troughs at the showgrounds.
• Daily mouth check: Look at lips, tongue, muzzle and coronary bands every day on the road and for two weeks after you return.
• Isolate returning horses: Keep them apart for a couple of weeks when you can.
• Check paperwork early: CVI timing, Coggins and any state VSV statement.
• Call the vet: Report any mouth sore, drooling or sudden refusal to eat before you load up.

For more habits that keep shows safe, see our show prep guide and health basics.

What to watch next

• APHIS situation reports. They list new and released premises by county, usually every week or so.
• The first hard freeze. Outbreaks typically end once cold weather kills the insects, though the virus can sometimes come back the next spring.
• Release dates. The Delta and Montezuma properties can't be released until at least 14 days after the last horse's sores began.
• Other barn bugs. Fall also brings strangles outbreaks and pigeon fever, so good biosecurity does double duty.