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An Unwelcome Sign of Summer: Vesicular Stomatitis

Katie LobertiAnimal Health, Livestock diseases Leave a Comment

Imagine looking forward to spending time with your horses during the summer, but finding them drooling with blistered tongues and muzzles. Unfortunately, this is what some farmers and equestrians in southwestern and midwestern areas of the United States are experiencing this summer because of an outbreak of vesicular stomatitis (VS).

VS is a zoonotic disease—caused by the VS virus (VSV)—and affects horses, cows, pigs, sheep, goats, llamas, alpacas and humans. VSV is known to have two serotypes (VSV-Indiana and VSV-New Jersey), meaning that this disease is caused by a virus that has two distinct variations in how animal immune systems respond to it. Both serotypes of VSV have been reported during the 2020 outbreak.

While the virus may not be life-threatening, it can harm a farm or ranch economically. The economic impact of a VS outbreak is estimated as a mean loss of $15,565 at any given infected ranch (Rozo-Lopez, P., et al., 2018). This implies that while livestock may survive an outbreak, the farm business could suffer greatly.

Where Is the VS Outbreak Occurring?

The 2020 outbreak was first reported in New Mexico, then in Arizona, Nebraska, Kansas and Texas (USDA APHIS, 2020). During 2014 and 2015, the VS outbreak was of the VSV-New Jersey serotype, and it was followed by a 2019 outbreak of the VSV-Indiana serotype. Remarkably, the last time there was an outbreak of both serotypes was in 1997-1998. In the current outbreak (which affected 122 animals as of July 7th), a majority of the infected animals were horses.

How Is VS Transmitted?

During an outbreak, shared feed buckets and other fomites are important means of transmission of VSV. Biting flies such as sand or black flies also can transmit the virus to animals (Rozo-Lopez, P., et al., 2018). In addition, non-blood eating insects such as eye gnats and houseflies can carry the virus. Outbreaks of VS are usually observed in the summer and fall when the population of black flies, biting midges and sandflies are at their highest. Diligent pest control is important for helping to prevent a VS outbreak. Pest control also protects animals from other insect-transmitted diseases.

How to Detect VS

VS can look like foot-and-mouth disease in cloven-hoofed animals. Both cause similar lesions, but only VS and not foot-and-mouth disease affects horses. Typically, one of the first clinical signs of VS in cows and horses is excessive salivation because of painful vesicles in the mouth. If lesions and blisters occur on the teats of dairy cattle, it can result in mastitis (inflammation of the udder tissue) and a decrease in milk production. Lameness due to foot lesions is usually the first clinical sign in pigs, however, it is also seen in horses and can lead to laminitis (USDA APHIS, 2019). Some signs to look for are:

  • White raised vesicles (fluid-filled cysts) within the mouth.
  • Blisters or sores on lips, tongue, gums, tops of hooves (coronary band), prepuce (sheath), nostrils, vulva, and teats.
  • Excessive salivation, drooling, or frothing.
  • Reluctance to eat or drink because of pain in the mouth.
  • Weight loss.
  • Fever.

Seeing blisters (the B of BUDDIES) or vesicles around the mouth, teats or hooves of any animal should trigger a call to a veterinarian. If VS is suspected, a definitive diagnosis is needed and a foreign animal disease diagnostician will collect samples and order appropriate laboratory testing (USDA APHIS, 2019). While the disease is typically non-lethal and runs its course in two weeks, it is vital to catch VS early to prevent its spread. Once VS is confirmed, work with your state veterinarian to contain the disease.

Protect Yourself Against VS

Protecting livestock from diseases is important, but farmers should consider their own well-being too. If VS is suspected or confirmed on a farm, be aware that VS can be also be transmitted to humans. While many sources claim VS transmission to humans is rare, it’s not impossible (Pelzel-McCluskey, 2020). A person with VS usually has a high fever, severe fatigue and body aches. While the disease is self-limiting and runs its course within three to five days, it can still make a person bedridden. Dr. Angela Pelzel McCluskey, equine epidemiologist for USDA APHIS Veterinary Services, recommends to:

  • Stay away from an infected animal’s face, especially if the animal is slobbering.
  • Always use gloves when examining the inside of an infected or potentially infected animal’s mouth or face. Be sure to thoroughly wash your hands after removing the gloves.
  • Always wear different clothing and shoes when dealing with infected animals. Change out of that clothing after leaving the area with infected animals.

Prevent the Spread of VS

There is no definite cure or treatment for VS other than supportive care (USDA APHIS, 2019). Consistently following biosecurity practices for sanitation and quarantine is a must on a farm, especially to prevent the introduction of a disease or slow its spread. Some recommended guidelines are:

  • Separate sick and healthy animals.
  • If possible, do not bring new or returning animals onto the property within 14 days of the last case of an outbreak. Quarantine new animals for a minimum of eight days (the virus’s incubation period).
  • Wash and sanitize hands and objects that have come into contact with infected animals.
  • Practice good fly control and management (fly tape, sugar water, keep animals in enclosures during dawn and dusk, etc.)
  • Avoid traveling to exhibitions if possible. Screen exhibitions for biosecurity policies and restrictions.
  • Before traveling with livestock, check for local and state restrictions that could limit access to certain states or prevent entry with animals altogether.

Animals that show signs of VS on a farm should be brought to the attention of a veterinarian and a state or federal animal health authority. Although VS is not lethal, it can sicken livestock, potentially infect people on the farm and severely impact the farm business. More information and specific biosecurity recommendations for livestock can be found on the Healthy Farms Healthy Agriculture website.


Rozo-Lopez, P., Drolet, B. S., & Londoño-Renteria, B. (2018). Vesicular Stomatitis Virus Transmission: A Comparison of Incriminated Vectors. Insects, 9(4), 190. Retrieved from https://doi.org/10.3390/insects9040190

US Department of Agriculture, Animal and Plant Health Inspection Services (2019). Vesicular Stomatitis [Fact sheet]. Retrieved from https://www.aphis.usda.gov/publications/animal_health/fs-vesicular-stomatitis.pdf

US Department of Agriculture, Animal and Plant Health Inspection Services (2020). 2020 Vesicular Stomatitis Situation Report. Retrieved from https://www.aphis.usda.gov/animal_health/downloads/animal_diseases/vsv/sitrep-07-02-20.pdf

Pelzel-McCluskey, A. (Presenter) & Hiney, K. (Host). (2020, July 23). Tack Box Talk [Podcast]. Retrieved from https://www.buzzsprout.com/242373/4689266

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About the Author

Katie Loberti

Katie Loberti was an undergraduate student at the University of Vermont pursuing a bachelor's degree in animal science. In the past, she worked as a park naturalist at Burlingame State Park in Rhode Island, which allowed her to grow and share her knowledge and passion for wildlife in New England with others. She also volunteered at Biomes Marine Biology Center in Rhode Island which helped her discover her love for aquatic life. At the University of Vermont, Katie was an active member of the women's rugby club. In the future, Katie hopes to pursue veterinary medicine or do work with animal conservation and education.

About the Editor

Joanna Cummings

Joanna Cummings received a Bachelor of Science in Horticulture from The Pennsylvania State University (PSU), with a specialization in vegetable crop and greenhouse production. At PSU, she was a research technician on no-tillage vegetable crop experiments, and a greenhouse assistant in the All-American Selections Research Gardens. Her career in the agriculture industry includes field research, work with dairy and vegetable farms, and as a greenhouse manager, estate gardener, landscaping and market garden entrepreneur. She transitioned to the science communication field after receiving a master of science degree in environmental communications from Antioch University New England. At Antioch, Joanna was a field botany laboratory teaching assistant, manager of the herbarium, and editor of the department's student newsletter, Notes and Niches. She currently works with Research Professor Julie M. Smith as a communications professional in the University of Vermont Animal and Veterinary Sciences Department. She is the webmaster for the Healthy Farms Healthy Agriculture website.

About the Editor

Dr. Julie Smith

Dr. Julie Smith is a research professor at the University of Vermont. Julie received her B.S. in biological sciences, D.V.M., and Ph.D. in animal nutrition at Cornell University. Since 2002, she has applied her veterinary background to programs in the areas of herd health, calf and heifer management, and agricultural emergency management. She has taught courses in animal welfare, calf biology and management, and ABCs of biosecurity to undergraduates, mostly in the Department of Animal and Veterinary Sciences. As a veterinarian and spouse of a dairy farmer, Julie is well aware of the animal health and well-being concerns of dairy animals. Julie has conducted trainings for Extension educators, livestock producers, and community members on the risks posed by a range of animal diseases, whether they already exist in the United States, exist outside of the United States, or pose a risk to both animal and human health. In all cases, she emphasizes the importance of awareness and prevention. In addition, she has led a number of projects on biosecurity and emergency disease preparedness.


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