Vesicular stomatitis is a viral disease that more commonly affects horses living in warmer climates. [1][2]

The disease typically results in blister-like lesions (referred to as vesicles) forming in and around the mouths of horses and other farm animals. This condition is usually self-limiting, meaning it resolves without medical intervention. [2][3][4]

A diagnosis of vesicular stomatitis can be made using specialized tests on collected blood or samples of active skin lesions. [1][2] Contact a veterinarian if vesicular stomatitis is suspected in your horse, as it is a reportable disease. [4]

Since no vaccines exist, strict biosecurity measures are critical to prevent its spread through the herd. Key measures include implementing proper disinfection and quarantine protocols, as well as controlling insect populations. [1][2][3][4]

Vesicular Stomatitis in Horses

Vesicular stomatitis (VS) is an infectious viral disease that belongs to the family of viruses known as Rhabdoviridae. [1][2]

Two viruses of the VS group are particularly significant in horses in the United States: vesicular stomatitis viruses (VSV) New Jersey and Indiana, named after the locations where they were first isolated in the early 1900s. [2]

VS is most common in warmer climates. In the southwestern United States, like California and Colorado, outbreaks of the disease are sporadic. This is in contrast to other, warmer climates like South America, Central America, and Mexico, where the disease is endemic, meaning it is always present. [1][2][3][4][5][6]

The disease is typically seasonal and is most prevalent in the summer to early fall (May to October). Vesicular stomatitis can affect all mammals, including farm animals such as cattle, pigs, sheep, goats, and llamas. [2][3][4]

The disease causes blister-like lesions on the body, known as vesicles. These lesions are typically found in and around the mouth. The inflammation caused by these blisters is referred to as stomatitis, which is where the name vesicular stomatitis is derived. [1]


Clinical signs can appear within 2-8 days of the initial infection. Many horses may exhibit a fever and drooling before other clinical signs develop. [2][7]

The most striking clinical signs associated with vesicular stomatitis are the blistering and ulceration caused by the disease. Blisters, ulcers, and eventually crusting lesions develop on hairless areas of the skin and the mucous membranes (nose, eyes, and gums). [2][3][4]

Lesions are most commonly found on the horse’s: [2][3][4]

  • Mouth
  • Lips
  • Tongue
  • Muzzle
  • Nose
  • Ears

Less commonly affected areas include: [2][3][4]

  • Coronary bands around the hoof
  • Udder or teats
  • Penis sheath and prepuce
  • Ventral abdomen

Lesions may appear as small spots, or they can coalesce and become large areas of erosions or ulcerations. [2]

Other Signs

Other more general clinical signs that may be noted secondary to these lesions include: [3][4]

A low percentage of infected animals do not develop clinical signs. [2][8][9]

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Vesicular stomatitis virus is primarily transmitted to horses through biting insects, including black flies, sand flies, and biting midges. Other biting insects suspected of spreading the disease include mosquitoes, deer flies, horse flies, and stable flies. [2][3][4][10][11][12]

The virus has also been isolated in non-biting insects such as house flies and house gnats, but their significance in the viral transmission of VS is unclear at this point. [13]

The virus can also be transmitted through direct contact, typically via contact with the open sores and saliva of infected individuals. However, some animals may shed the virus as quickly as one day after becoming infected, before showing any visible symptoms. [2][3][4][14]

Equipment that has been in contact with infected animals can also carry the virus and further spread it to other animals and horses on the farm. Items such as buckets, trailers, feed, bedding, and water troughs are important items that may contain infectious viral particles. [4]

Disease Progression

Biting flies become infected with the virus by feeding on an animal with VS. Flies must feed on areas with skin lesions to acquire the virus, as VSV-infected mammals do not have high levels of circulating virus in their bloodstream. [15][16]

These insects can then shed the virus in their saliva, spreading it to other mammals during subsequent blood meals. Infected biting insects may also spread the virus to other non-infected biting insects if they feed in close proximity to each other on a mammal. [2][6][11][15][16][17]

Once a horse contracts VS, the virus causes cell death and fluid buildup between the superficial layers of the skin. This separation of the layers leads to the blister-like lesions, or vesicles, that are characteristic of this disease. [2][18]

Vesicles typically form within 24-48 hours of contracting the disease. However, it can take up to 8 days from the time a horse becomes infected with the virus to when they show clinical signs.

The vesicles quickly disappear as they rupture and the top layer of skin is lost, or as fluid from the lesion escapes. Once this occurs, erosions and ulcers become the most prominent lesions. As these lesions heal, crusting and scabbing become more prominent. [2][4][7][18]


Vesicular stomatitis in horses is suspected based on the skin lesions it causes, but the disease must be confirmed using specialized tests. [4]

These tests can be performed using the horse’s blood or by collecting fluid, skin, or swabs from fresh lesions. [1][2]

Once a diagnosis is made, veterinarians must notify the state and federal animal health authorities, since vesicular stomatitis is a reportable disease[3][4]

Blood Tests

Blood can be collected and tested for antibodies against the virus to confirm a diagnosis of VS. This type of test is also referred to as a serologic test.

The specific types of serologic testing that may be used to diagnose vesicular stomatitis include: [2][4][13]

  • Competitive enzyme-linked immunosorbent assay (C-ELISA)
  • Indirect enzyme-linked immunosorbent assay (I-ELISA)
  • Virus or serum neutralization

To diagnose an active infection of VS, two samples of blood are collected and compared. The increase in antibodies between the two samples helps distinguish animals that have been previously exposed to the virus from those that have an active infection. [2][13]

These serologic tests are considered the gold standard for diagnosing vesicular stomatitis virus in horses and are also the test of choice used in health screenings for international trade of horses. [2][13]

Serologic tests can also be used to distinguish which type of VS (vesicular stomatitis virus New Jersey versus Indiana) is affecting the animal. [13]

Viral Testing

Viral isolation is performed by identifying viral particles in a tissue sample, also known as virus neutralization. The main method for this is polymerase chain reaction (PCR) assays.

Several fluids and tissues can be used for virus isolation, including: [4][19][20][21][22]

  • Any sample from the vesicles themselves, including swabs, fluids, and the skin on our around them
  • Flaps of skin remaining after the rupture of vesicles
  • Serum collected from blood

Microscopic Diagnosis

Biopsies collected from active lesions from affected animals may also be submitted to the laboratory to support a diagnosis of vesicular disease. [13]

During vesicular stomatitis, active viral replication occurs in the skin layer known as the stratum spinosum. When the tissue biopsy sample is examined microscopically, the viral replication is characterized by swelling and death of the skin cells, called keratinocytes, leading to the formation of a pocket of fluid. Other inflammatory cells are also visible in samples from these lesions. [13][23]

Special staining techniques, such as in situ hybridization and immunohistochemistry, can also be performed on processed tissues collected for microscopic diagnosis. These tests visibly highlight viral particles in the affected tissue. [23]

Differential Diagnosis

When diagnosing vesicular diseases, your veterinarian will not only consider infectious diseases but also non-infectious ones as potential causes. [3]

Other infectious diseases that can occasionally cause erosive to ulcerative lesions in or around the mouth of horses include: [2][24]

If other animals on the farm are affected by vesicular lesions, an important disease to consider is foot and mouth disease (FMD). FMD is indistinguishable from VS, but it does not affect horses. Likewise, swine vesicular disease and vesicular exanthema of swine are also indistinguishable from VS clinically, but only affect pigs. [1][4]

Non-infectious diseases that can also cause similar ulcerative lesions to VS include: [2][4][24][25]

Treatment and Prognosis

Vesicular stomatitis often resolves without intervention within 2 weeks. In more severe cases, lesions can take up to 2 months to heal. [2][3][4]

During the time horses have active lesions, the following supportive care can be offered: [2][3][4]

  • Soft feed to reduce pain while eating
  • Anti-inflammatory medications to decrease inflammation and pain
  • Intravenous fluids for horses reluctant to eat or drink
  • Flushing the mouth with antiseptics such as chlorhexidine

Cleaning sores and using antiseptics can reduce the risk of secondary infections. Antibiotic treatment is often necessary if sores become infected by bacteria. [3][4]

While VS is typically self-limiting, it can have a significant financial impact, mainly due to the cancellation of horse shows and events during outbreaks in the area. [4]


Isolating affected horses as well as strict biosecurity measures minimize the risk of reinfection and further spread throughout the farm. [2][3]

Animal Management

Upon diagnosis, horses are required to quarantine to prevent further spread of the disease. Quarantines last for at least 2 weeks following the last reported case on the property or until active lesions subside. [4]

It is also important to minimize the spread of disease between animals through direct contact with humans. Owners, veterinarians, farriers, and other staff in contact with infected animals should take care to minimize transmission between animals. This can be achieved by washing hands or changing gloves between contact with animals. Large operations may elect to have designated handlers for infected and uninfected animals. [4]

General Biosecurity Measures

Several preventive measures can be taken before an outbreak of vesicular stomatitis occurs. Examples of effective biosecurity steps that can be used to minimize or prevent infectious diseases on your farm include: [1][4]

  • Isolating new horses for at least 21 days
  • Providing adequate nutrition, deworming, exercise, vaccinations, and regular veterinary care
  • Observing horses and isolating any sick animals
  • Providing food and water individually rather than using communal equipment
  • Cleaning and disinfecting equipment regularly
  • Emptying standing water to minimize biting insect populations

Viral particles from VS are easily destroyed making this disease easily preventable with appropriate biosecurity measures. Viral particles become inactive from exposure to sunlight and heat and are effectively killed using most commercially available disinfectants. [4][13]

Insect Population Control

Limiting exposure to biting insects can reduce further transmission of the disease. In addition to emptying standing water to reduce overall insect populations, sheltering horses during dusk and dawn can decrease their exposure to biting insects. [3][15][26]


While there are vaccines that have been developed for experimental use, there are currently no vaccines commercially available against VSV in North America. [4]

A VSV vaccine was developed and used during outbreaks in the United States in the past, but its efficacy is unknown. Some countries in Latin American do have commercially available vaccinations against VSV. [2][3][27]

Is Vesicular Stomatitis a Zoonotic Risk to Humans?

VS can be transmitted to humans through contact with horse saliva or fluid from open sores. Humans typically develop flu-like symptoms such as fever, muscle pain, and fatigue, and rarely develop blisters. If symptoms develop in humans after contact with a VS-infected horse, a healthcare professional should be contacted. [2][4][28]

Humans can minimize risk of self-infection from vesicular stomatitis virus by: [4]

  • Wearing latex gloves while handling sick, affected horses
  • Minimizing contact with open sores caused by VS
  • Standing to the side of horses and avoiding being in front of them to prevent being sneezed on, which can spray viral particles


Vesicular stomatitis is an infectious viral disease that can affect all mammals, including horses.

  • The primary symptom of vesicular stomatitis is blister-like lesions on the skin, usually most noticeable on the lips and mouth
  • VS is a reportable disease; any confirmed cases must be reported to local animal authorities
  • VS can spread between different animals, including humans and other farm animals
  • VS usually resolves without medical intervention
  • Robust biosecurity measures provide the best chance of minimizing outbreaks and preventing further spread

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