Colorado health officials say a squirrel in Morrison was found to have bubonic plague.
It's the first case of plague in the country and could spread to people and other animals if precautions aren't taken.
But they say risk of contracting the bubonic plague is extremely low.
Plague is spread by the bite of infected fleas and symptoms include fever, chills, headache, vomiting and swelling of lymph nodes within two to seven days of exposure.
It can be treated with antibiotics when within 24 hours of showing symptoms.