Yersinia Pestis and Plague
Yersinia pestis (the bacteria that cause plague) is found in animals throughout certain parts of the world and causes about 1,000 to 3,000 cases of plague each year. The bacteria are found most commonly in rats, but occasionally in other animals.
Yersinia pestis can grow with or without oxygen. Animals that are known to carry the organism (besides rats) include prairie dogs, squirrels, and fleas. During an outbreak, the bacteria is able to survive for months in cool, moist conditions, such as the soil of a rodent hole. Approximately 10 to 20 people in the United States develop infections each year from flea or rodent bites.
(Click Yersinia Pestis for more information on this topic, including statistics and information on infections in humans and who is at risk for developing them.)