On May 17, 2023, a confirmed case of Vesicular Stomatitis (VSV) was reported by the National Veterinary Services Laboratories, according to the U.S. Department of Agriculture. The case originated from one equine premise in San Diego County, California, affecting one 11-year-old Quarter Horse mare.
As of June 9, 2023, over 77 affected equine premises have been reported, all in California (29 positive, 48 suspect). United States Equestrian Federation (USEF) licensed horse shows have implemented new guidelines for competition; equine industry media outlets are closely following the outbreak. As the virus spreads, horse owners across the country are asking – what is Vesicular Stomatitis, how is it transmitted, and is my horse at risk?
Vesicular Stomatitis and its symptoms
Vesicular Stomatitis, or VSV, is a contagious disease affecting horses and other livestock animals such as cattle and swine. In horses, VSV presents as blister-like lesions that typically appear on their tongue, lining of the mouth, nose, or lips – sometimes even on coronary bands, the udder, or sheath. Symptoms will usually appear in 2-8 days after the first exposure and can include:
- A fever
- Blisters forming
- Drooling or frothing at the mouth followed by a possible reluctance to eat
- Possible weight loss
- Possible lameness or laminitis (if the coronary band is affected)
VSV is formally diagnosed through a blood test to identify virus-specific antibodies, or by testing swabs from the lesions. Testing is important to confirm that the lesions aren’t from another cause, such as sunburns or other irritations.
Humans are also at risk of infection from exposure to the virus, so proper biosafety measures should be implemented and followed strictly, such as wearing latex gloves and prompt hand washing after handling infected animals. The symptoms in infected humans can feel like the flu, including headaches, fever, muscle aches and fatigue.
What causes Vesicular Stomatitis?
According to the U.S. Department of Agriculture, known vectors for VSV include black flies, sand flies, and biting midges. For this particular outbreak, it was indicated that in the first 4 identified affected premises that the likely source of infection was indeed from VSV-infected insects.
The disease can also be transmitted through physical contact between animals – horse-to-horse by contact with saliva, or the fluid from ruptured blisters. It’s also cautioned that contact with items or surfaces touched by an infected horse such as buckets, feed, bedding, or shared water troughs can contribute to the disease spreading.
The importance of fly & insect control
There are multiple measures you can take for your horse and your facility when it comes to fly control, from spray-on repellents to facility management. But why is it so important to do all of these things? Bugs are more than just pesky pests that cause your horse to stomp and swish – they can be carriers of many diseases that can make your horse seriously ill.
It’s up to us to make an impact on the fly population, and reduce the risk of our horses contracting and transmitting diseases carried by insects like black flies.
For spray-on repellents to combat flies, UltraShield® EX Insecticide & Repellent and UltraShield® Red Insecticide & Repellent are proven to repel and kill black flies, sand flies, and biting midges.
How is Vesicular Stomatitis treated?
Unfortunately, there is no specific drug or treatment for Vesicular Stomatitis, and little else to do than wait for the virus to run its course. The American Association of Equine Practitioners (AAEP) recommends helping your horse stay comfortable while they experience and recover from VSV, including:
- Giving soft feeds to relieve oral discomfort
- Providing anti-inflammatory medications to minimize swelling and pain
- Flushing the mouth
Though Vesicular Stomatitis typically clears up within two weeks, the AAEP cautions that it may take as long as two months for the lesions to completely heal. It’s also important to remember that the live virus can be “isolated” from the lesions for up to a week after they first appear, during which time the horse is still infectious and poses a risk to spread the disease to other animals.
Because of this, quarantine is critical. VSV is what is called a “reportable disease,” meaning that even in a suspect case, your veterinarian must contact state and federal animal health authorities. In confirmed cases, your facility must be quarantined for at least 14 days.
How you can mitigate the risk of Vesicular Stomatitis
Viral outbreaks can be scary! The good news is there’s a lot you can do to mitigate the risk of Vesicular Stomatitis.
For your horse
- Healthy horses have a better chance of fighting disease! Provide proper nutrition, regular exercise, and stay up-to-date on deworming and routine vaccinations.
- With new horses, make sure to quarantine them for at least 21 days (3 weeks) before introducing them into a herd or barn.
- Keep a close eye on your equine friends. If they start to show any signs of infection, immediately isolate them and contact your veterinarian.
- Maintain good fly control measures – apply fly repellent often and generously, and consider wearables such as fly masks, fly sheets, and fly boots.
Around the farm
- Keep up with manure management and eliminate standing water or muddy areas. Bugs breed here!
- Clean and disinfect feeders, buckets, trailers, and other equipment regularly.
- Use individual rather than shared buckets, feeders, and equipment if possible.
- Wash your hands and always be sure to use latex gloves if handling a horse with suspected VSV or any other illness.
- Stay informed. The Equine Disease Communication Center offers an interactive map with alerts from the USDA and other government agencies state-by-state, as well as a library chock-full of resources on infectious disease education, biosecurity, vaccinations and more.
Vesicular Stomatitis in Horses, American Association of Equine Practitioners. https://aaep.org/horsehealth/vesicular-stomatitis-horses
2023 Vesicular Stomatitis Virus (VSV) Situation Report, U.S. Department of Agriculture Animal and Plant Health Inspection Service. https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/cattle-disease-information/vesicular-stomatitis-info
Update: Vesicular Stomatitis in California, Practical Horseman Magazine. https://practicalhorsemanmag.com/health-archive/ph-edcc-health-watch/update-vesicular-stomatitis-in-california/
Disease Alerts – California, Equine Disease Communication Center. https://equinediseasecc.org/alerts
Competition Safety and Biosecurity, United States Equestrian Federation. https://www.usef.org/compete/resources-forms/competition-management/competition-safety-biosecurity