Plague (cont.)

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What is plague?

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Plague is generally defined as epidemic disease or affliction that causes high mortality or widespread calamity or misery (for example, the biblical plagues of Egypt cited in the Bible). However, the first definition, in most medical dictionaries, defines plague as a disease caused by bacteria. This article will only discuss plague as caused by the bacterium Yersinia pestis.

The Yersinia pestis bacterium causes plague, a disease that is endemic in some animal populations (mainly rodents). This bacterium can be transmitted to humans, usually by a vector such as fleas. Plague usually starts with a flea bite in which Y. pestis is transmitted from the flea bite site to lymph nodes that swell (buboes). This type of plague is termed bubonic plague. The bacteria can spread into the bloodstream and eventually infect other organs. In some patients, the bacteria can enter the bloodstream without lymph node swelling (termed septicemic plague); in others, the patients can inhale or swallow droplets that contain Y. pestis that infect the lungs (termed pneumonic plague). Death occurs in about 50%-90% of all people who develop infection with Y. pestis and are not treated; even with treatment, about 15% of infected people will still die. Epidemics of this devastating disease have occurred many times in the past. Skin areas and buboes in untreated people may become dark or a black color as the disease progresses, so plague was originally termed "Black Death." In addition, it has been associated with the term pestilence that the Merriam-Webster Dictionary defines as "a contagious or infectious epidemic disease that is virulent and devastating; especially: bubonic plague."

What is the history of the plague?

Plague or Black Death has been mentioned in most regions of the world for centuries. In 1347, 12 ships arrived in Sicily after a trading mission from the Black Sea. Most of the sailors died during the return trip. They had fever, severe pain, vomiting, and black boils that exuded blood and pus. The disease was thus termed the "Black Death." The port authorities ordered the ships out of the port, but the infection had already spread. Over the next five years, plague or Black Death killed about one-third of Europe's population, or about 20 million people. Once it became established in a population before effective treatments were established, it would rapidly travel through a population in a settlement, town, or city and kill so many people that historians said there were not enough people left alive to bury all of the dead. During the 17th and 18th century, "plague doctors," who only treated plague patients, wore elaborate plague masks filled with aromatic items like spices and perfumes to protect themselves from the "bad air." Like their patients, many plague doctors still died from the plague as the masks offered no significant protection.

In 1894, two investigators, Dr. Alexandre Yersin and Dr. Shibasaburo Kitasato, almost simultaneously described bipolar staining organisms in buboes and organs of people who died from plague. Yersin also deduced the connection between rats and plague; the organism was named Yersinia after Yersin. Dr. Paul-Louis Simond, in 1898, discovered the vector of the disease was a flea. Recent research on Y. pestis has shown that the organisms have not significantly changed their genetic material in about the last 660 years. Bacterial genomes, found in bodies buried in mass graves due to a plague epidemic in London (1347-1351), showed very minor changes when compared to current Y. pestis strains, so the current strains have not changed significantly since the Middle Ages in Europe.

Plague or its cause, Y. pestis, has been used by humans as a weapon (bioterrorist weapon) against other humans for centuries, including this current time. In medieval times, bodies of plague victims were hurled over city walls in an attempt to infect many inhabitants and thus weaken the defense capability of a city. Currently, the CDC considers Y. pestis a category A microbial agent for potential or actual use as a weapon for use against other humans. Although people may be vaccinated (but the vaccine is not readily available to most individuals) or treated with antibiotics, the organism is still attractive to some biological weapons designers because Y. pestis may be aerosolized (for example, Y. pestis may be placed in droplets or small inhalable particles that may be sprayed by several methods into the air) and thus easily inhaled by unprotected individuals to produce a rapidly debilitating or lethal infection in many individuals exposed to the aerosol. Although most world countries say this type of weapon should never be used, the potential for development and use is likely to be at least explored or even exploited by some individuals.

Medically Reviewed by a Doctor on 10/30/2013

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