Vesicular Stomatitis (VS) is a viral disease of horses, cattle, and other livestock living in the Western hemisphere--with outbreaks reported in South America, Central America, Mexico, and the Southwestern United States. The disease is characterized by the appearance of short-lived vesicles which turn into ulcers and erosions inside and outside the horse's mouth, tongue, nasal mucosae, and occasionally the coronary bands. It is caused by infection with either of two serotypes of the vesicular stomatitis virus (VSV)---the VSV New Jersey (VS-NJ) or VSV Indiana (VSV-IND). Approximately 30% of infected animals on a property with an outbreak develop clinical signs of disease.
Clinical Signs of Vesicular Stomatitis
Approximately 70% of affected animals will show no overt signs of disease. Those who do develop signs, usually will develop blanched areas after 1-3 days of exposure, which turn into vesicles--which appear as lesions on the tongue, lips, corners of the mouth, gums, and around the muzzle and nostrils. On rare occasions, horses may develop coronitis in the coronary band area, along with swelling and inflammation. Others may develop lesions on mammary glands and external genitalia. Lesions are usually raised, blanched and occasionally fluid-filled vesicles. Vesicles will quickly rupture, leaving ulcerations and erosions which usually heal within 7 to 14 days.
How Vesicular Stomatitis is Transmitted
VSV is primarily spread by insects---sandflies, mosquitoes, deerflies, horseflies, biting midges, houseflies, eye gnats, black flies, and stable flies. There is also speculation that the VS virus is a plant virus found in pasture grasses. Being an arbovirus, outbreaks of VS usually occur during peak insect growth seasons, which starts in late spring or early summer and continues through to late fall.