Vesicular Stomatitis in Horses, Cows, and Pigs

Vesicular stomatitis (VS) is a viral disease of horses, cattle and swine that produces characteristic lesions known as vesicles and erosions. After a short incubation period of anywhere from 3 to 15 days, affected animals will have an elevated temperature, appear lethargic (depressed) and anorexic, and often exhibit drooling of saliva (ptyalism) and lameness.

The characteristic sign of VS is the development of vesicles. Vesicles are blister-like lesions that are elevations of the epidermis up to 1 cm in diameter and are filled with clear fluid. Vesicles are typically fragile and transient in appearance, usually giving way to erosions. Erosions are shallow epidermal defects or ulcers that expose the underlying dermis. Vesicles develop on the tongue, dental pad, gums, lips, coronary band and interdigital cleft of the feet. Vesicles may also develop on the teats and on the udder, particularly in lactating cows and sows. Occasionally, vesicles may develop on the prepuce. Areas of skin subject to pressure and trauma such as the legs of pigs housed on concrete may also develop vesicles. The period of fever and vesicle formation is short lived. Due to the fragile nature of vesicles, erosions are the more commonly seen lesion. Erosions tend to heal in from 4 to 7 days, although hoof deformities may require attention for several months to years but are a rare occurrence. VS is also zoonotic (transmissible to humans) and may cause flu-like symptoms in people.

VS is endemic in South and Central America as well as Mexico. The VS virus has not been known to occur outside of the Western Hemisphere. There are two known serotypes of the VS virus; one is called the New Jersey strain which is the most common and virulent variety, while the other is known as the Indiana serotype. In the United States, occasional outbreaks are seen, with both serotypes having been isolated. In endemic areas, the occurrence of VS is often seasonal and associated with the transition from rainy to dry periods of the year.

The VS virus is spread by direct contact between infected individuals as well as by blood-sucking insects. Saliva and vesicular fluid from clinically affected animals are highly infective and contain large numbers of virus. VS virus has been isolated from convalescent cattle 38 days after the absence of clinical signs of disease. Stress can cause a recurrence during convalescence. In the Western portions of the United States, black flies (Simulidae) are responsible for disease transmission and sand flies (Lutzomyia) are the more common vectors seen in endemic areas. Additional insects may act as mechanical vectors.

VS is caused by an RNA containing virus of the genus Vesciculovirus, which is a member of the family Rhabdoviridae. As a group, vesicular diseases are clinically indistinguishable from one another. Foot and Mouth Disease (FMD), vesicular stomatitis (VS), swine vesicular disease and vesicular exanthema are all such vesicular diseases. One primary difference between VS and FMD is that horses not affected by FMD will become clinically ill with VS.

The morbidity rate is low with VS, typically seen at a 10 to 20% level, but in a dairy herd, a morbidity level of 80% is not unheard of. On the other hand, seroprevalence in a herd may approach 100%.

Immunity after an attack of VS appears to be of short duration and is suspected to be no more than 6 months.

A wildlife reservoir is suspected but has not yet been identified. Deer, feral pigs, rodents, raccoons, bats, birds, and even lizards have been infected with the VS virus.

Although VS is painful, the disease is not fatal. Treatment is primarily supportive, involving pain relief and treatment for the lesions in order to prevent secondary infection. In severe cases, corrective shoeing may be necessary. There is no approved commercial vaccine available in the United States. An autogenous killed vaccine is available in Central America and was temporarily approved during the 1995 outbreak for use in the U.S. in dairy cattle but the efficacy of the vaccine could not be determined. VS is a reportable disease in the United States and prevention consists of vector control, early detection, protective clothing, strict hygiene, and a 30 day quarantine following the absence of clinical disease.

To determine the type of virus causing a clinically apparent vesicular disease in a nonendemic area, samples of vesicular epithelium or vesicular fluid should be sent in phosphate-buffered saline (pH 7.4) to a national laboratory. Samples may also be tested at the World Reference Laboratory for vesicular diseases which is located in Pirbright, UK by prior arrangement. Strict regulations exist concerning the shipment of pathologic and hazardous materials.

References:

Brown, Christopher and Joseph Bertone. The 5-Minute Veterinary Consult Equine. Blackwell Publishing. 2005. pp. 1120-1121.

Kahn, Cynthia Editor. The Merck Veterinary Manual. Merck & Co. 9^th Edition. pp. 555-546.

Orsini, James and Thomas Divers. Equine Emergencies Treatment and Procedures. Saunders/Elsevier. 3^rd Edition. p. 714.

Radostits, Otto and Clive Gay et all. Veterinary Medicine. W.B. Saunders 10^th Edition. 2007. pp. 1232-1235.

“Vesicular Stomatitis.” Animal Health Newsletter. Alabama Department of Agriculture and Industries, USDA, APHIS, Veterinary Services. Vol. 2, Issue l. January/February 2008. p. 1.