A virus outbreak that affects mainly horses and cattle is on the rise in Montezuma and La Plata counties.

In mid-July, the Colorado Department of Agriculture announced two horses in La Plata County tested positive for the vesicular stomatitis virus.

Keith Roehr, Colorado state veterinarian, said Monday that number has jumped to 54 confirmed cases in La Plata County.

In Montezuma County 18 cases have been confirmed. Statewide, there have been about 475 investigations into suspected vesicular stomatitis cases, with 287 animals actively quarantined. About 30 animals have been released.

La Plata County is in the top four counties in the state with the most outbreaks: Larimer has 93, Boulder has 48 and Weld has 43 confirmed cases. Archuleta County has 10 confirmed cases.

So what’s causing the outbreak? The disease is not completely understood, Roehr said, but it can be transmitted through flies and insects.

Outbreaks aren’t all that common, he said. Since 1994, there have been only six outbreaks in Colorado, not including this year. It’s suspected that increased rainfall and vegetation allows for fly breeding grounds to thrive, possibly leading to an uptick in animals contracting the virus, Roehr said. The most recent outbreak is affecting horses; there has been only one infected steer, in Boulder County.

Roehr said he was not aware of any horses that have died because of the virus, but it’s “not out of the realm of possibilities.” He said most animals recover with minor care. “But it can be very painful, and it can take an extended period of time to completely heal,” he said.

Symptoms of vesicular stomatitis can include excessive salivation, lesions in the mouth, nostrils and feet, lack of appetite and lameness.

Roehr said if people who own horses or other livestock start to notice their animal exhibiting these symptoms, they typically contact their veterinarian, who in turn, contacts the state’s Department of Agriculture if vesicular stomatitis is suspected.

Owners can voluntarily quarantine the animal for two weeks, or get a test to confirm the disease, then quarantine the animal for two weeks.

Treatment during this time is symptomatic but can include cleaning lesions with antiseptic solutions or providing animals with mouth lesions with softer food.

Prevention methods include strict fly control around a property, such as eliminating fly breeding areas and proper insecticide use for livestock and barn areas.

Manure management and removing wet bedding are other ways to prevent the spread of the disease, Roehr said.

“If people do apply fly control … the risk can be minimized significantly,” he said.

Anyone who has animals they suspect of having the vesicular stomatitis virus should report it to state officials at (303) 869-9130.

jromeo@durangoherald.com