Vesicular Stomatitis in Horses

What Is Vesicular Stomatitis in Horses?

Vesicular stomatitis is a highly contagious viral disease seen in horses in the Western Hemisphere. The virus can also affect other farm animals such as cows, sheep, and goats, as well as humans.

The disease is named after the characteristic blister-like lesions, ulcers, and crusts that form around the mouth, nose, genitals, and coronary band. Though very painful, it’s rarely life-threatening.

The disease is widespread in southern Mexico and Central America. It is seen sporadically in the United States, most commonly during warm summer months.

Symptoms of Vesicular Stomatitis in Horses

• Drooling

• Frothing at the mouth

• Reluctance to eat

• Fever

• Blister-like lesions around the mouth, nose, genitals, or coronary band

• Ulcers on the tongue or gums

• Lameness (if lesions develop around the coronary band)

Causes of Vesicular Stomatitis in Horses

Vesicular stomatitis is caused by a virus spread by biting insects (such as black flies, sand flies, biting midges), animal-to-animal contact, and contaminated surfaces or equipment. There are two strains of the virus: the vesicular stomatitis New Jersey (VSNJ) virus and vesicular stomatitis Indiana (VSI) virus. The two viruses differ in their genetic makeup but cause the same disease process and symptoms.

Other conditions may resemble vesicular stomatitis, including:

• Physical trauma: chemical burn, electrocution from hot wire or fence, lightning strike

• Dietary factor: sunburn, irritating weeds, or grain

• Toxins: blister beetle toxicity, non-steroidal anti-inflammatory toxicity

• Immune mediated disorder: Cushing’s disease

These need to be ruled out when a case of vesicular stomatitis is suspected.

How Veterinarians Diagnose Vesicular Stomatitis in Horses

A thorough history and physical exam are the first steps to diagnose vesicular stomatitis. Key information about travel or exposure to new horses is vital. Your veterinarian will look for blister-like lesions or ulcers in and around the mouth and nose, near the genitals, and the feet.

A confirmed diagnosis of vesicular stomatitis is made by submitting blood samples and swabs of the lesions to a diagnostic laboratory. The laboratory will look for antibodies to the virus in the blood. This will indicate that the virus was present in the horse and the horse’s body produced antibodies in response to it. The swabs will also identify the presence of the virus. 

Vesicular stomatitis is a reportable disease, meaning a positive case will need to be reported to the state and federal authorities to help with containment and prevention.

Treatment of Vesicular Stomatitis in Horses

Treating vesicular stomatitis is done through supportive care, as the lesions are quite painful. Anti-inflammatory medications like phenylbutazone and flunixin meglumine are used to alleviate pain, swelling, and inflammation.

If your horse is having trouble eating, softening their grain or hay cubes with warm water may help. Additional treatment with intravenous fluids may be necessary if your horse is at risk of becoming dehydrated from not drinking.

If secondary infections develop at the lesion sites (indicated by pus), antibiotics may be prescribed. Rinsing the lesions with an antiseptic solution, like dilute chlorhexidine, may help reduce secondary bacterial infections.

Recovery and Management of Vesicular Stomatitis in Horses

The first step in managing vesicular stomatitis is to set up a quarantine. This will include isolating the affected horse from other animals for 14 days since the last lesion was identified. 

When caring for and handling sick horses, use personal protective equipment and proper biosecurity practices to prevent the spread of the disease to other horses. This includes wearing gloves to handle an affected horse, as well as disinfecting your shoes and clothes that have been around the affected horse. Do not share tack or other equipment between horses.

Most horses diagnosed with vesicular stomatitis make a complete recovery within a few weeks. In rare cases, vesicular stomatitis can lead to dehydration, colic, and laminitis. Horses that are not drinking enough water because their oral cavity is too painful are susceptible to dehydration and impaction colic. Laminitis can be seen in horses with severe lesions around their coronary bands.

Because the virus is spread by biting insects, direct contact, and contaminated surfaces or equipment, containing the virus and eliminating spread of the disease requires cleaning anything that encounters an infected horse and keeping the horse’s housing area as clean as possible.

Other preventative measures include:

• Isolating new horses for 21 days before introducing them to a barn or herd

• Keeping insects at a minimum by eliminating manure and standing pools of water, and by using fly control

• Keeping horses healthy with good nutrition, deworming, and routine vaccines

• Immediately isolating any horses that show signs of infection and contacting your veterinarian

• Using individual feed/water buckets and grooming equipment

Humans can also become infected with vesicular stomatitis. Therefore, it is extremely important to wear gloves when handling infected horses and avoid contact with the horse’s saliva and fluid from the blisters.