Kathy Anderson, Extension Horse Specialist, University of Nebraska
Vesicular stomatitis is a viral disease which affects horses, cattle, swine, and occasionally sheep and goats. Additionally, numerous species of wild animals including deer, bobcats, goats, raccoons and monkeys are susceptible. The virus causing vesicular stomatitis can also infect handlers of infected animals.
Vesicular stomatitis most commonly occurs during warm months in the Southwest region of the United States, particularly along river ways and in valleys. Recent outbreaks in the Southwest have occurred from May to December in 1995, 1998, and 2005. Livestock owners and veterinarians must stay alert for animals displaying signs characteristic of this disease.
Blister-like lesions may form in the mouth and on the dental pad, tongue, lips, nostrils, hooves, and teats of infected animals. These blisters swell and break, leaving raw tissue so painful that infected animals go off feed and water, suffer mild-to-severe weight loss, and may show signs of lameness.
Aside from the economic loss to livestock producers, vesicular stomatitis is significant because the outward signs are similar to (but less severe than) those of foot-and-mouth disease. Foot-and-mouth disease is a devastating foreign disease of cloven-hooved animals that has not occurred in the United States since 1929. The only method to differentiate between these diseases is through laboratory tests.
Because of the similarity of vesicular stomatitis to foot-and-mouth disease, the potential negative impact on livestock production, and its public health implications, the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS)works to keep this disease from becoming established in the United States. Vesicular stomatitis is recognized internationally as a reportable disease, and exports of livestock, horses, and animal products from the U.S. would be restricted if vesicular stomatitis were allowed to spread here.
The incubation period for vesicular stomatitis is two to eight days. The most common early signs are excessive salivation and drooling. Increased body temperature may occur either immediately before or at the same time as lesions develop.
Close examination reveals blister-like lesions on gums and lips; lesions may also occur on the nostrils, teats, and coronary bands. In horses, the lesions generally occur on the upper surface of the tongue. In cattle, lesions usually appear on the hard palate, lips and gums sometimes extend to the muzzle and nostrils.
When blisters break open, painful ulcers develop that cause horses to drool and froth from the mouth. This sign can be mistaken for bitting problems, dental abnormalities or colic. Infected animals generally go off feed and suffer mild to significant weight loss. Additionally, mild lameness may occur if lesions develop along the coronary band. Some cases of severe lameness have been reported in horses with sloughed hooves.
The number of affected animals on a property varies. Five to 10 percent of horses within an infected herd typically show clinical signs. If there are no complications such as secondary infections, affected horses may recover in as little as two weeks. However, more severe cases can take up to two months to heal; horses continue to be contagious during this time. Animals rarely die from vesicular stomatitis.
Vesicular stomatitis has been confirmed only in North and South America. The disease is endemic in warmer regions of the Western Hemisphere, but outbreaks occasionally occur in temperate geographic areas.
How vesicular stomatitis spreads is not fully understood; insect vectors, mechanical transmission and movement of animals are all believed to play a role. One type of vesicular stomatitis is known to be spread by phlebotomine (bloodsucking) sandflies. Once introduced onto a property, the disease apparently moves from animal to animal by contact or exposure to saliva or fluid from ruptured blisters.
Humans can contract vesicular stomatitis by not following proper biosafety practices when handling affected animals. Prevalence of this disease in humans may be under-reported because it often goes undetected or is misdiagnosed.
In people, vesicular stomatitis causes acute influenza-like illness with symptoms such as fever, muscle aches, headache and malaise. People who handle potentially infected horses should wear gloves and shouldn't allow saliva and blister fluids to come in contact with open wounds or mucous membranes such as the eyes or mouth. Producers and other individuals who handle horses and who experience symptoms of illness should contact their physicians immediately.
Laboratory blood tests can be used to diagnose vesicular stomatitis. Additionally, the virus can be isolated from epithelium around vesicles or from vesicular fluid. Veterinarians need to differentiate between vesicles in the mouth caused by vesicular stomatitis and vesicles caused by photosensitization or trauma due to rough feed. Other vesicular viral diseases such as foot-and-mouth disease don't occur in horses.
There isn't any specific treatment or cure for vesicular stomatitis other than supportive care. Owners can protect their animals from this disease by not allowing animals to congregate in an area where vesicular stomatitis has occurred. Mild antiseptic mouthwashes may provide comfort and more rapid recovery to an affected horse. Good sanitation and quarantine practices on affected farms usually contain the infection until it dies out of its own accord.
When a definite diagnosis is made on a farm, the following procedures are recommended:
The majority of horse owners with infected animals will suffer economic losses in caring for sick animals. In an effort to assess the financial impact of vesicular stomatitis, New Mexico horse owners were surveyed following the 1995 outbreak in the Western U.S. Costs, including labor, veterinary fees, and medicine were estimated at $115 for each infected horse.
Restricting horse movement and refraining from participation in events should prevent spread of vesicular stomatitis, but such restrictions may cause additional economic losses. When a horse tests positive for the disease, generally it isn't allowed to move between states or nations. Infected horses also aren't allowed to compete in most shows, rodeos, fairs, and other events. When such events are canceled due to an outbreak, owners of healthy horses suffer as well.
Health certificates issued within 24 to 48 hours of transport may be required to bring a horse to some facilities or move it across state lines. Additionally, certain events may require that each horse be examined for lesions before being allowed on the grounds. Horse owners should check to determine restrictions before moving horses.
Veterinarians and livestock owners who suspect an animal may have vesicular stomatitis or any other vesicular disease should immediately contact State or Federal animal health authorities. To report suspect cases or answers to questions regarding vesicular stomatitis in Nebraska, contact the Nebraska State Veterinarian at 402/471-2351.
For more information, contact USDA, APHIS, Veterinary Services Emergency Programs 4700 River Road, Unit 41, Riverdale, MD 207371231, (301) 734-8073.