Vesicular stomatitis, also known as sore mouth of cattle and horses, or Indiana fever, is a viral infection that affects horses, cattle, swine, wild animals, and humans. The disease takes its name from the vesicles (blisters) that form during the acute stage of the infection at various sites of the body. Vesicular stomatitis is a reportable disease in most areas, including the United States. The causative agent of vesicular stomatitis is the virus of the genus Vesiculovirus (VSV), family Rhabdoviridae. Important infections caused by Rhabdoviridae viruses include rabies, and ephemeral fever (three-day sickness). The Vesiculovirus virus is a bullet-shaped, enveloped, single-stranded RNA virus which is easily inactivated by iodine, quaternary ammonium compounds, phenolic compounds, and chlorine. 5 The virus is not stable in the environment outside living hosts, but survives for years at ultralow temperatures (-70 °C). 6
Currently four viruses are known to cause vesicular stomatitis: vesicular stomatitis Indiana virus (VSV-IN; formerly known as the Indiana 1 subtype of VSV); vesicular stomatitis New Jersey virus (VSV-NJ; vesicular stomatitis Alagoas virus (VSV-AV; formerly Indiana 3) and Cocal virus (formerly Indiana 2). 4 Both blood- and non-blood-feeding insects are suspected to transmit the viruses including black flies, sand flies, face flies, eye-gnats or eye flies, mosquitoes, and midges (Culicoides). Cattle that ingest experimentally infected grasshoppers may become infected. 2,3 Once introduced into a herd, the virus moves from animal to animal primarily by contact or exposure to saliva or fluid from ruptured lesions. 8
Excess salivation and and fever often are the first signs of infection in cattle and horses, while lameness is the first sign in swine. In horses, vesicles (blisters) are most often seen on the lips, gums, nostrils, in the corners of the mouth, and cushions of the hoof. Blisters vary greatly in size from pea-size to lesions that cover the entire surface of the tongue. Blisters break revealing painful ulcers that cause refusal to drink and eat. 1,3 Vesicles may not be seen because they quickly rupture leaving ulcerated areas beneath. Crusting lesions of the muzzle, lower abdomen, the covering of the penis, and udder of horses are typical during outbreaks in the southwestern US. Diagnostic samples may be submitted to the National Veterinary Services Laboratory (NVSL) in Ames, Iowa for vesicular stomatitis antibody testing.
Because the disease is contagious, animals diagnosed with vesicular stomatitis should be isolated. All surfaces contaminated with saliva must be thoroughly disinfected. Establishing an effective fly control program will help in preventing spreading of the disease. Although no specific treatment is needed, supportive therapy is important. Offer soft feed and clean ulcers with mild antiseptic to prevent bacterial infections. The disease usually resolves with several weeks. However, reinfection can occur following a second exposure. Deaths from vesicular stomatitis are rare and are mostly due to secondary bacterial infections that affect vital organs. 5,7
Natural human infections with VSV are common throughout much of tropical America. Human vesicular stomatitis virus infection is an acute illness that resembles influenza. The incubation period is usually 3 to 4 days, but can be as short as 24 hours. Symptoms may include fever, muscle pain, headache and malaise. Blisters are rare, but can be seen in the mouth, on the lips, or hands. Most people recover without complication in 4 to 7 days. 4