As of Aug. 2, the Department of Agriculture had confirmed 23 cases of vesicular stomatitis in horses and 15 cases in cattle in Colorado. The USDA confirmed several cases of vesicular stomatitis in Texas in May, and cases in New Mexico in June.

The tristate outbreak is the first vesicular stomatitis outbreak in the United States since 1998. At press time, there were more than 100 confirmed cases in horses and cattle, and at least 62 premises quarantined in the three states.

Vesicular stomatitis outbreaks occur periodically in the United States. The disease can cause great concern when livestock are affected because its clinical signs mimic those of foot-and-mouth disease in susceptible species, and FMD has not been seen in the United States since 1929. Horses are not susceptible to FMD, so that was ruled out in the cases involving horses. However, when cattle, pigs, sheep, or other cloven-hooved animals develop signs such as sores and blisters, laboratory tests must be run to differentiate between the two diseases.

The virus that causes vesicular stomatitis is transmitted by arthropods. It also may be passed from animal to animal when saliva or the fluid from ruptured blisters contaminates equipment or feed. Humans also may contract vesicular stomatitis and develop flulike symptoms.

More information about vesicular stomatitis is available at the USDA Animal and Plant Health Inspection Service's Web site, www.aphis.usda.gov/lpa/issues/vs/vs.html.