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Plague is an infectious disease caused by bacteria called Yersinia pestis. These bacteria are found mainly in rodents, particularly rats, and in the fleas that feed on them. Other animals and humans usually contract the bacteria from rodent or flea bites.

white-throated wood rat
A white-throated woodrat, Neotoma albigula, in its Southwestern U.S. arid habitat. This, and other woodrat species, harbor fleas known to carry Yersinia pestis bacteria, which may be transmitted to human beings through flea bites.
Credit: CDC

Historically, plague destroyed entire civilizations. In the 1300s, the "Black Death," as it was called, killed approximately one-third (20 to 30 million) of Europe's population. In the mid-1800s, it killed 12 million people in China. Today, thanks to better living conditions, antibiotics, and improved sanitation, current World Health Organization statistics show there were only 783 cases in 2013 worldwide.

In recent decades, an average of 7 people per year in the United States develop plague, according to the Centers for Disease Control and Prevention. There has not been a case of person-to-person infection in the United States since 1924.


Last Updated January 06, 2015