Scientists have confirmed cases of vesicular stomatitis in horses in New Mexico and Arizona. The cases are the first to be identified in the United States in 2005.

Vesicular stomatitis affects primarily cattle, swine, and horses, and has been found in many other animals. The disease can cause great concern if livestock are affected, because clinical signs mimic those of foot-and-mouth disease, which hasn't been identified in the United States since 1929. When animals that are susceptible to FMD viruses develop signs, such as sores and blisters, laboratory tests must be performed to differentiate between the two diseases.

Foot-and-mouth disease has been found in cattle, swine, sheep, and other cloven-hoofed animals. Although horses are not susceptible to FMD viruses, the Department of Agriculture issues alerts when vesicular stomatitis is found in horses because of the possibility that the viruses that causes the disease will spread to other livestock, producing signs that can be confused with FMD.

On April 27, the National Veterinary Services Laboratories in Ames, Iowa, confirmed finding the New Jersey strain of VS virus in two horses at one premises in Grant County, New Mexico. The affected premises had six horses and approximately 110 head of cattle. By May 10, the disease had been identified in five horses on three premises in New Mexico and three horses on three premises in Arizona. The premises were put under quarantine, and officials are working diligently to contain the outbreak. At press time, investigators had not identified the disease in FMD-virus-susceptible animals.

In May 2004, vesicular stomatitis was identified in Texas and soon discovered in New Mexico and Colorado. That tristate outbreak was the first in the United States since 1998.

During the eight-month outbreak, a total of 294 premises were quarantined under state authority. On these quarantined premises, 405 equids, 63 bovids, and two llamas were infected with VS-NJ virus. By mid-January, the last premise deemed VS-NJ virus positive, located in Colorado, was released from quarantine, after satisfying a 30-day period in which no new disease occurred.