(NBC News) — National Park Service rangers warn that a rare virus is sickening and killing wild cottontail rabbits in Dinosaur National Monument.

Visitors to the park, which spans Colorado and Utah, are urged to take caution and not approach any wildlife, particularly wild rabbits, because of confirmed cases of rabbit hemorrhagic disease, or RHDV2, which caused by a highly contagious and lethal virus.

Dinosaur National Monument spokesperson Dan Johnson said the virus’s effect on rabbits is brutal and almost always deadly: “They often have a bloody froth at the mouth.”

Park rangers first noticed large numbers of dead rabbits around early March, Johnson said, and the park released the news of the confirmed cases as soon as the test results came back this week.

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