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.
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 2,118 cases in 2003 worldwide.
Approximately 10 to 20 people in the United States develop plague each year from flea or rodent bites—primarily from infected prairie dogs—in rural areas of the southwestern United States. About one in seven of those infected die from the disease. There has not been a case of person-to-person infection in the United States since 1924.
Worldwide, there have been small plague outbreaks in Asia, Africa, and South America.
Last Updated May 23, 2007
Last Reviewed May 23, 2007