What Is a Plague?
Epidemics used to be referred to as plagues. Epidemics are an unexpected increase in the number of cases in a location over a defined period of time. Pandemics are worldwide epidemics. Different organisms have caused pandemics throughout history.
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Epidemics
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Plague is an outdated word to describe an epidemic. An epidemic is any increase in the number of cases of a particular disease beyond what is expected for a place during a particular time. For example, if a hospital only sees 10 cases of pneumonia in an average January, an epidemic would be more than 10 cases in January at that hospital. For extremely rare diseases, like anthrax or smallpox, just one case at any time is an epidemic.
Pandemics
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A pandemic is an epidemic that has spread to the entire world. According to the World Health Organization, the H1N1 Pandemic of 2009 was declared as such after sustained person-to-person transmission of the virus was confirmed in two continents. The term pandemic refers to the geographic distribution of an epidemic, not how many are afflicted or if those afflicted are severely ill. Pandemics have occurred periodically and have been caused by different infections.
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Black Death
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In the 14th century, fleas on rats carried the Yersinia pestis bacteria from Asia to Europe, sparking an epidemic that killed millions in Europe. While the exact number of deaths is not known, an estimated 50 to 75 million people died from the infection. The term pestilence is a derivative of the Latin word "pestis", which referred to the Black Death epidemic.
Influenza
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Influenza has causes numerous pandemics throughout history. The most severe on record is the 1918 pandemic that killed between 20 and 40 million people around the world. Even with vaccines available, the virus mutates faster than vaccine manufacturers can produce a vaccine. The mutations promote the viruses' transmission from person-to-person. Most recently, the 2009 H1N1 influenza pandemic was declared to be the fastest to span the globe by the World Health Organization.
HIV
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The human immunodeficiency virus (HIV) is a virus that infects and destroys the human immune system. The virus was first discovered in the early 1980's in the United States and it has become a pandemic. By 2009, it is estimated to have killed more than 25 million people around the world since 1981, according to avert.org.
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