Tests performed on the cat indicated that it had the disease. A blood sample from the cat has been sent to the Colorado Department of Public Health and Environment for confirmation of the diagnosis. Plague is caused by a bacterium, Yersinia pestis , carried by fleas that infest wild animals, including rats, prairie dogs, rabbits and squirrels. It is transmitted to humans by flea bites experienced when a person is walking through a rodent-infested area, and through direct contact with infected animals. Fleas are aggressive parasites and will readily bite other animals, particularly if their natural hosts are killed.
Domestic pets can also contract plague by eating infected animals or by being bitten by fleas.
We see it every year. Plague, a bacterial disease which killed 28 million Europeans during the Middle Ages, was introduced to North America by rat-infested ships. Because it cannot be effectively eliminated from the animal population, plague is always a threat. The incidence of human cases tends to rise and fall in cycles lasting several years. Cats and dogs may carry fleas home to their owners, or may serve as a direct source of infection through body fluids.