Vesicular stomatitis

Oral Blisters and Drooling in Horses

Vesicular Stomatitis Katie Delph, DVM

Vesicular stomatitis is a viral disease that affects not only horses, but also donkeys, mules, cattle, and pigs. The virus is transmitted by insect vectors (gnats and biting flies). Once infected, the virus can be spread by animal-to-animal contact with saliva or fluid from blisters and contact with contaminated equipment or human hands.

In horses, blisters of the lips, gums, and tongue develop and quickly turn to ulcerations when the blisters rupture. These ulcerations are painful and cause reluctance to eat, difficulty swallowing, and drooling. Weight loss may occur as a result of decreased feed intake. Abrasions or trauma may increase the susceptibility to infection. Ulcerations can sometimes occur on the udder, sheath, or coronary bands of horses. Lesions on the coronary band can cause lameness. Fever may occur as blisters are forming.

If your horse develops any of the signs consistent with vesicular stomatitis including drooling, reluctance to eat, or blisters on his gums or tongue, please contact your veterinarian. Vesicular stomatitis is a reportable disease; therefore, your veterinarian will contact state and federal regulatory veterinarians to inform them of a possible case. Diagnostics include serum samples to test for antibodies to the virus or sampling of the blisters in order to detect the virus. Testing occurs at the USDA National Veterinary Services Laboratory in Ames, IA, and results are typically available within a week.

In the meantime, the affected horse should be separated from healthy horses and movement on and off the farm should be stopped. Vesicular stomatitis is contagious and an outbreak could occur if appropriate isolation and quarantine are not followed. Outbreaks tend to occur in waves. This year US cases have been reported in Arizona, Colorado, New Mexico, South Dakota, Texas, Utah, Wyoming, and most recently, Nebraska. The outbreak began in April of 2015 and currently 5 states (Colorado, New Mexico, South Dakota, Utah and Wyoming) have premises under quarantine still.

Treatment of affected horses is largely supportive while ulcers heal. Anti-inflammatory medications and soft feeds may help encourage feed intake if the horse is painful. Antibiotics may be warranted to prevent secondary infections if the ulcerations are severe. The horse will continue to be able to spread the virus until the ulcers are completely healed. The disease generally resolves within 2 weeks but may take up to 2 months for lesions to completely heal. Regulatory veterinarians will help organize and maintain quarantine on affected premises.

Prevention of vesicular stomatitis includes isolating new horses on a premises for 3 weeks, avoiding contact with new horses at events, cleaning equipment regularly, feeding horses with individual buckets, insect control, and monitoring and separating horses with any signs of illness.

Humans are rarely infected with vesicular stomatitis; however, infections have occurred. Clinical signs in people typically include flu-like symptoms. If you have concerns that there may be human exposure or illness, please contact your primary care physician. It is important to understand the zoonotic potential of this virus so that horse caregivers wear protective equipment including gloves when handling a suspect or diagnosed case of vesicular stomatitis.

Equestrian events as well as traveling between states and other countries may be affected by a vesicular stomatitis outbreak so plan ahead when needing to travel. Your veterinarian can contact your state or country of destination and determine if there are any restrictions on movement.