HOUSTON – A squirrel in Denver has tested positive for bubonic plague, Colorado officials say. The squirrel was found in the town of Morrison, and is the first case of plague in the county. The plague is caused by the bacteria Yersinia pestis, and can be contracted by humans and household animals if proper precautions are not taken, authorities say. Cats are highly susceptible to plague and may die if not treated promptly with antibiotics. Dogs are not as susceptible to plague; however, they may pick up and carry plague-infected rodent fleas.