Two horses in Weld County have tested positive for vesicular stomatitis, a virus that can make eating and drinking painful, and the equines have been quarantined.

Colorado is the third state in the country this year to confirm cases of vesicular stomatitis, according to a state Department of Agriculture news release. Cases have also been diagnosed in Kinney and Tom Green counties, Texas, and in Sandoval County, N.M.

On Wednesday the National Veterinary Services Laboratory reported positive test results on samples submitted from two Weld County horses at different locations.

“Vesicular stomatitis can be painful for animals and costly to their owners,” said Keith Roehr, state veterinarian, in the release. “The virus typically causes oral blisters and sores that can be painful, causing difficulty in eating and drinking.”

The animals are being monitored daily and will remain under quarantine for at least two weeks from the onset of lesions. There are no USDA-approved vaccines for vesicular stomatitis.

The viral disease is transmitted by insects — black flies, sand flies and biting midges. In a herd, it can spread from horse to horse. Humans can become infected when handling sick animals, but it’s rare. To avoid exposure, people should take personal protective measures when handling affected animals.