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Vesicular Stomatitis Virus (VSV)

The infectious disease known as vesicular stomatitis virus (VSV) was a problem in Colorado during summer of 2014. The virus infected hundreds of horses, some cattle, and forced the quarantine of more than 200 properties, most in northern Colorado. Colorado State University veterinarians worked closely with the Colorado State Veterinarian’s Office and officials with the U.S. Department of Agriculture to understand the VSV outbreak, to care for horses, and to provide information to protect animals from the spread of disease.

Here is a list of frequently asked questions, answered by Dr. Paul Morley, a Colorado State University veterinarian and director of infection control for the university's James L. Voss Veterinary Teaching Hospital. This information is provided to coincide with the Colorado State Fair in August, but is relevant for all horse and livestock owners and to virtually any type of event. Additional information, including video from a CSU interactive online presentation is below.

Question: What are the symptoms of VSV?

The main symptoms of vesicular stomatitis virus are blisters, sores, and sloughing of skin in the mouth, on the tongue, on the muzzle and ears, and above the hooves. Lameness and weight loss may also occur. Horses have been hit hardest during this summer’s outbreak in Colorado, although several cows have been confirmed as infected. Weld, Boulder and Larimer counties in northern Colorado have the highest number of confirmed cases. VSV can threaten a number of other livestock species, including sheep, goats and pigs.

Question: Why is VSV so concerning that it is prompting quarantines?

VSV is federally listed as a foreign animal disease, meaning it is among several animal diseases that are highly infectious, are reported to state and federal health agencies, and are monitored closely by health officials because of the potential for widespread illness and devastating economic consequences. The U.S. Department of Agriculture requires a specific list of responses to foreign animal diseases, including testing, confirmation of infection, quarantine and monitoring. These steps allow for proper diagnosis and help stop spread of disease.   

Question: How is VSV spread?

Flies and midges are the main vectors for VSV. The virus also is spread through direct contact, meaning when an infected animal touches noses with another animal. Indirect contact is also a concern; this occurs when an infected animal sheds virus onto something – like a water bucket, a trailer, a tie-out rail, or grooming equipment – and then another animal picks up the virus from that object.

Question: How is VSV infection prevented?

Fly control is the most important step, and should be taken very seriously. We recommend frequent application of fly repellent approved for animals, including on the face and ears. We also advise use of barriers, such as fly sheets and face masks.

Infection risk may be further reduced by sheltering horses during peak times for biting attacks. Those times typically are mid-morning, with a more intense phase in evening, ending at dusk, according to CSU insect scientists. Biting intensifies at the onset of storms and may persist all day when overcast conditions occur.

In addition, I recommend basic steps to prevent infectious disease when traveling to events with your horse, as outlined in this video: In a nutshell, these steps are:

  • Separate your horse from others during the show.
  • Don’t share tack or feeding, watering, and grooming equipment. Don’t tie your horse where others have been tied. Keep hands off other horses, and avoid letting other people handle your horse.
  • Disinfect all show and travel equipment, including trailer, before and after use.
  • Frequently wash hands and use hand sanitizer.
  • Sgregate your traveling horse from others for a week after returning home; monitor your horse for any signs of infection or illness during this time.
  • Contact your veterinarian for more information.

Question: How do you protect horses and other patients at the CSU Veterinary Teaching Hospital?

Our primary mission is to provide the best care possible for our patients and their owners, even during outbreaks such as this. Preventing the spread of infectious disease is central to our hospital’s daily operations, and rigorous standards are always in place to protect patients. During this outbreak we have initiated extra precautions in line with those recommended by the state veterinarian for the Colorado State Fair and other events. Our veterinarians first examine all horses and livestock for VSV symptoms before they enter the hospital. We question owners about travel history to ascertain infection risk. If an animal is admitted to the hospital, it is treated twice daily with insect repellent; our entire large animal hospital is additionally sprayed three times daily. We also use biological insect controls to minimize populations of insect vectors. Housing patients indoors further reduces infection risk. We continuously clean, and all animals are constantly monitored for signs of VSV or other infectious disease. During the current outbreak, we have cared for patients with VSV – and those suspected of having the disease – on their home premises.

Question: What would happen if my animal was at an event or a veterinary hospital when another animal was diagnosed with VS infection?

The Colorado State Veterinarian’s Office and U.S. Department of Agriculture officials would be notified, as is required by law. They would help analyze infection risks and would determine appropriate next steps. If preventative measures, such as those described above, had been followed – and assuming your animal had no signs of infection – your animal would be allowed to travel home.  Officials have worked very hard to help people during this outbreak.

Question: Who determines whether shows and events will be cancelled, and why haven’t we seen more cancellations during this VSV outbreak?

Event sponsors and organizers make those decisions, usually on advice of the state veterinarian and other health experts. Dr. Keith Roehr, the state veterinarian for Colorado, has not recommended event cancellations. Instead, he has encouraged that event grounds be inspected and issued certificates of veterinary inspection before the start of shows and events. This helps ensure that event hosts are taking appropriate preventative measures. Most shows require that competitors have health certificates issued by veterinarians as proof of good animal health. Dr. Roehr has also strongly advised that horse and livestock owners take extra caution in controlling flies, and I agree.

Question: Do I need to worry about travel restrictions?

Travel restrictions come into play if you are transporting horses or livestock to a different state. Officials in the destination state manage these restrictions. To find out about any such restrictions, visit and click on "Import Requirements." 


VSV Presentation and Q&A

Did you miss our online presentation and Q&A about Colorado’s fast-growing outbreak of the vesicular stomatitis virus? Watch the full video now, where experts from our equine hospital and the USDA answered your questions about the infectious disease.


 Paging Dr. Ram: Vesicular Stomatitis


Don't have time to watch the entire hour-long presentation? No problem. Click on the links below and watch only the questions that matter to you. Questions? Email

More information on VSV: