Plague

"Plague" is a term used to describe an infectious disease that affects humans and some animals. The Yersinia pestis bacteria are responsible for it, and actually cause three types of plague: bubonic plague, septicemic plague, and pneumonic plague. If left untreated, the mortality rate is 50 to 90 percent. If treated early (typically with antibiotics), the rate drops to 15 percent.
 

What Is Plague?

Plague is an acute, infectious disease of humans, rodents, and ectoparasites (fleas and lice).
 

History of Plague

Throughout history, plague has 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, plague killed 12 million people in China. Thanks to better living conditions, antibiotics, and improved sanitation, plague is rare these days, occurring in a few thousand people worldwide each year.
 

The Cause of Plague

Plague is caused by bacteria called Yersinia pestis. These plague 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.
 
(Click Plague and Animals for more information.)
 

Types of Plague

A Yersinia pestis infection can cause one of three forms of plague:
 
Depending on the circumstances, these forms of plague may occur separately or in combination.
 
(Click Types of Plague for more information.)
 
(Plague Continued: Page 2)
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Written by/reviewed by: Arthur Schoenstadt, MD
Last reviewed by: Arthur Schoenstadt, MD