Vesicular stomatitis is a viral disease that causes painful, blister-like sores in cattle, horses, and swine. It’s caused by a rhabdovirus that circulates primarily through insect bites, and while most animals recover fully within about two weeks, the disease triggers serious regulatory concern because its symptoms look nearly identical to foot-and-mouth disease, one of the most economically devastating livestock diseases in the world.
The Virus Behind It
Vesicular stomatitis virus (VSV) belongs to the Rhabdoviridae family, the same broad family that includes rabies. Two distinct strains cause virtually all outbreaks: VSV-New Jersey and VSV-Indiana. Together, these two strains are responsible for hundreds to thousands of outbreaks annually in southern Mexico, Central America, and northern South America. In the United States, outbreaks occur less predictably, often flaring up in western states during warmer months and then disappearing for years at a time.
Symptoms in Livestock
After an incubation period of 2 to 8 days, infected animals typically develop a fever followed by fluid-filled blisters. These vesicles form in and around the mouth, on the nose, along the lips, and on the coronary bands just above the hooves. In some animals, lesions also appear on the udders, sheath, or abdomen.
The most visible sign in cattle and horses is excessive drooling or frothing at the mouth, which happens because the blisters make eating and drinking painful. In horses specifically, the sores often present as crusting scabs on the muzzle, lips, ears, and coronary bands. When lesions develop around the hooves, animals may become noticeably lame or develop laminitis, a painful inflammation of the hoof tissue.
The disease is generally self-limiting. If no secondary bacterial infection sets in, most animals recover completely within 10 to 14 days. The biggest practical problems during that window are weight loss from reluctance to eat and reduced milk production in dairy cattle.
How It Spreads
The exact transmission cycle of vesicular stomatitis is not fully understood, but biting insects are the primary carriers. Black flies, sand flies, and biting midges have all been shown capable of transmitting the virus, though other insects may play a role as well. This is why outbreaks tend to spike in warm, humid months and cluster near rivers, streams, irrigation canals, and other bodies of water where these insects breed.
Once the virus enters a herd, it can also spread from animal to animal through direct contact. Saliva and the fluid from ruptured blisters are highly infectious. Shared water troughs, feed buckets, and other equipment can carry the virus between animals even without direct nose-to-nose contact.
Why It Matters for Livestock Trade
Vesicular stomatitis produces symptoms that are clinically indistinguishable from foot-and-mouth disease (FMD). Since FMD is far more contagious and economically devastating, any animal with blister-like mouth sores must be tested to rule it out. This means a single suspected case of vesicular stomatitis can trigger quarantines, halt animal movement across state lines, and disrupt livestock sales until laboratory results come back.
Vesicular stomatitis is a nationally reportable disease. Veterinarians, diagnostic labs, and animal health professionals are required to report confirmed or suspected cases to both state animal health officials and USDA APHIS (Animal and Plant Health Inspection Service). Quarantine zones are typically established around affected premises, and animals cannot be moved until they are cleared.
How It’s Diagnosed
Because the blisters look identical to those caused by foot-and-mouth disease, laboratory testing is the only way to confirm vesicular stomatitis. Veterinarians collect samples from the fluid inside blisters, tissue from lesion edges, or swabs of active sores.
The fastest lab method is a competitive ELISA blood test, which can return results the same day a sample arrives. Complement fixation testing is also a one-day procedure, though samples are often not processed immediately due to the length of the setup. A third option, virus neutralization, takes 2 to 3 days to complete. All three are internationally recognized tests used for trade certification, which is part of why rapid diagnosis matters so much for producers.
Risk to Humans
Vesicular stomatitis can infect people, though it rarely does. Humans who handle infected animals or come into contact with saliva and blister fluid are most at risk. The resulting illness is mild: fever, muscle aches, headache, and fatigue that typically resolve in 3 to 5 days. Actual blister-like lesions in humans have been documented but are rare.
Research from a Colorado outbreak found that people who examined the oral cavities of infected animals were at higher risk, particularly those who had open cuts or wounds on their hands or arms. People working with infected horses faced greater exposure risk than those handling cattle. Wearing gloves and washing hands thoroughly after contact with any symptomatic animal are simple, effective precautions.
Prevention and Biosecurity
There is no widely available vaccine for vesicular stomatitis in the United States, so prevention centers on reducing insect exposure and limiting animal-to-animal spread. The most effective environmental strategy is reducing insect habitat. Removing manure regularly cuts down breeding sites for biting midges, and propane-fueled insect traps placed strategically around a property can reduce local populations of flying insects.
Physical barriers also help. Installing fine mesh screens (with a pore size small enough to block midges) on barn windows, doors, and stall openings keeps insects away from housed animals. Repellent-treated fabric draped around stalls or used as outdoor netting adds another layer of protection.
During active outbreaks, moving animals away from water sources like rivers, ponds, and irrigation ditches reduces their contact with the insects that carry the virus. Keeping animals sheltered during peak insect activity hours, typically dawn and dusk, further lowers risk. Even after a frost kills off most adult insects, animals should not be returned to high-risk areas until quarantines have been lifted or no symptomatic animals remain on nearby properties.
Basic herd management matters too. Isolating new arrivals before mixing them with resident animals, not sharing equipment between affected and healthy herds, and disinfecting water troughs and feed buckets all help prevent the virus from moving through a barn once it has been introduced.