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10 Worst Epidemics

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by: Robert Lamb
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A street performer poses as the Grim Reaper for a small crowd. Ironically, the emergence of epidemic diseases closely follows the rise of crowded cities.
©iStockphoto.com/Neil German

­Few words in the English language encapsulate as much horror, misery and doom as "plague." After all, infectious diseases have inflicted a great deal of damage throughout the centuries. They've decimated whole populations, ended blood lines, claimed higher casualties than wars and played pivotal roles in charting the course of history.

Early humans were no strangers to disease. They encountered the microbes that cause illness in drinking water, food and the environment. Occasionally an outbreak might decimate a small group, but they never encountered anything close to the widespread illnesses of the ages to follow. It wasn't until humans began gathering in larger populations that contagious diseases had the opportunity to spread to epidemic proportions. An epidemic occurs when a disease affects a disproportionally large number of people within a given population, such as a city or geographic region. If it affects even greater numbers and a wider area, these outbreaks become pandemics.

Humans also opened themselves up to new and deadlier diseases by domesticating animals that boast their own microbes. By putting themselves in regular, close contact with formerly wild animals, early farmers gave these microbes a chance to adapt to human hosts.

As humans expanded their territory, they came into closer contact with microbes they might otherwise have never encountered. By storing food, humans attracted scavenging creatures such as rats and mice, which brought more microbes. Human expansion also resulted in the construction of more wells and ditches, which provided more standing water for disease-carrying mosquitoes. As technology allowed for wider travel and trade, new microbes could easily spread from one highly populated area to another.

Ironically, many of the pillars of modern human society paved the way for one of its greatest threats. And just as we continue to grow, so too microbes continue to evolve. In this article, we'll take a look at 10 of the worst epidemics to ever plague mankind and how each disease works.

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