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Plague Disease (Black Death)

Facts on the Plague

  • Plague is an infectious disease caused by plague bacillus (bacterium), Yersinia pestis.
  • It spreads easily and can be fatal if not treated.
  • The plague, known as the "Black Death," caused more fear and terror than perhaps any other infectious disease in history. It killed nearly 200 million people during the Middle Ages and has produced monumental social changes, such as marking the end of the Dark Ages and causing the advancement of clinical research in medicine.
  • Although still debated by historians, the plague has been responsible for multiple epidemics and at least three great pandemics (epidemics that are spread over a large region or multiple sections of the world).
    • The first plague pandemic spanned from the Middle East to the Mediterranean basin during the fifth and sixth centuries, killing about half the population of those areas.
    • The second pandemic struck Europe between the eighth and 14th centuries, destroying nearly 40% of Europe's population.
    • The third pandemic started in 1855 in China and spread to every major continent.
  • Alexandre Yersin isolated the bacterium (germ) that causes plague, developed a treatment (an antiserum) to combat the disease, and was the first to suggest that fleas and rats may have been spreading plague during the epidemic of 1894. The plague bacillus (bacterium) was named Yersinia pestis in Yersin's memory.
  • Pandemics have succeeded in spreading the plague to every major continent, with the possible exception of Australia. Unlike smallpox, the plague cannot be wiped out. It lives in millions of animals and on billions of the fleas that live on those animals. The plague is a disease of the desert, the steppes, the mountains, and the forest.
    • In the U.S., about seven cases per year have been reported during the last few decades. These cases are the mildest form of the illness, and they occur mostly in the Southwest. Prairie dogs and squirrels are vulnerable to contracting the plague in some western states, such as New Mexico, Arizona, Colorado, Utah, and California.
    • The World Health Organization reported 3,248 cases of plague worldwide, including 584 deaths. The number of actual cases is probably much higher because many countries fail to diagnose and report the plague. The following countries have reported the most cases of humans infected with the plague since 1979 (in order of most reported cases): Tanzania, Vietnam, Zaire, Peru, Madagascar, Burma, Brazil, Uganda, China, and the U.S.
    • The three countries with recent outbreaks of the plague are the Democratic Republic of the Congo, Madagascar, and Peru.
      • Madagascar has been experiencing an outbreak of plague. From August to October 2017 there have been 1,801 human cases and 127 deaths.
  • More recently there has been a concern that forms of the plague could be used as biological weapons in a bioterrorism attack.
Medically Reviewed by a Doctor on 11/21/2017

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Plague & Biological Warfare

In the United States, most victims with human plague have the bubonic form. If the organisms were used as a biological warfare agent, it most likely would be spread through the air and inhaled by victims. The result would be primary pneumonic plague (epidemic pneumonia).

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