Реферат: Bubonic Plague Essay Research Paper The Black
Bubonic Plague Essay, Research Paper
The Black DeathThe Black Death was the name given to an epidemic of bubonic plague that devastated Europe in the mid-14th century, so-called because of the black spots that appeared on the bodies of the victims. Spread by fleas that had fed on the blood of infected rodents, the plague is estimated to have killed off from 25% to 50% of the European population between 1347 and 1351. The Black Death erupted in the Gobi Desert in the late 1320s. No one really knows why. The plague bacillus was alive and active long before that; indeed Europe itself had suffered an epidemic in the 6th century. However, the disease had lain relatively dormant in the succeeding centuries. The climate of Earth began to cool in the 14th century, and perhaps this so-called little Ice Age had something to do with it. The Black Death came in three forms, the bubonic, pneumonic, and septicemic. Each different form of plague killed people in a vicious way. All forms were caused by a bacterium called Yersinia pestis. Yersinia was formerly classified in the family Pasteurellaceae. Based on the DNA and the DNA hybridization similarities to Escherichia coli, the Yersinia group has been reclassified as members of the Enterobacteriaceae family. Though there are 11 named species in the genus Yersinia, only 3 are considered important human pathogens. Y. pestis, the etiologic agent of plague, and the enteropathogenic strains, Y. pseudotuberculosis and Y. enterocolitica. Y. pseudotuberculosis is the closest genetic relative to Y. pestis but can be distinguished from the plague bacteria by its clinical manifestations and by laboratory test results. Both Y. pestis and Y. pseudotuberculosis do not frequently infect humans in contrast to Y. enterocolitica, which may be more commonly found in clinical specimens. The bubonic plague was the most commonly seen form of the Black Death. The mortality rate was 30-75%. The symptoms were enlarged and inflamed lymph nodes, mostly around armpits, neck and groin. The term bubonic refers to the characteristic bubo or enlarged lymphatic gland. The inflamed lymph nodes become filled with pus, and the disease spreads through the body by way of the infected bloodstream and the lymphatic system. Victims were subject to headaches, nausea, aching joints, fever of 101-105 degrees Fahrenheit, vomiting, and a general feeling of illness. Symptoms took from 1-7 days to appear. Fleas that have fed on the blood of infected rodents, usually rats, transmit the bacterium. The ingested plague bacteria multiply in the flea’s upper digestive tract and eventually obstruct it. When the flea feeds again on a human or another rodent, the obstruction causes the freshly ingested blood to be regurgitated back into the bite, along with plague bacteria. The circulatory system of the bitten individual then carries the bacteria throughout the body. During the Medieval time period 90% of untreated cases resulted in death within a few days.The pneumonic plague was the second most commonly seen form of the Black Death. The pneumonic and the septicemic plague were probably seen less then the bubonic plague because the victims often died before they could reach other places, caused by the inefficiency of transportation. The mortality rate for the pneumonic plague was 90-95%. If treated today the mortality rate would be 5-10%. Pneumonic plague was acquired by inhaling infected droplets from the lungs of someone whose plague infection has spread to the respiratory system. Symptoms included slimy sputum tinted with blood. Sputum is saliva mixed with mucus exerted from the respiratory system. This is the most contagious form of the disease and the form that progresses most rapidly, with death usually occurring in less than three days in virtually all untreated cases.
The septicemic plague was the most rare form of all. The mortality was close to 100%; even today there is no treatment. Symptoms were a high fever and skin turning deep shades of purple due to respiratory failure. Victims usually died the same day symptoms appeared. In some cities as many as 800 people died each day from the plague. Respiratory transmission was mainly responsible for the historic plague epidemics that swept across entire continents and wiped out tens of millions of people. One such epidemic killed an estimated 100 million people in the Middle East, Europe, and Asia during the 6th century. The Black Death, another epidemic in the same regions during the 14th century killed one-fourth to one-half the population of Europe, or about 75 million people. The most effective way to prevent plague is to reduce the rodent and flea populations by the use of proper sanitation and rodenticides and insecticides. The plague organism is vulnerable to the antibiotics streptomycin, chloramphenicol, and tetracycline, if treatment is started within about 15 hours of the first appearance of symptoms. All patients with bubonic plague should be strictly isolated for a period of at least 48 hours after treatment has been initiated. The more effective drug against Y. pestis is streptomycin, especially with pneumonic plague. However due to its toxicity, it should generally be given for only around 5 days. Tetracycline can be given concurrently and used to complete the full 10 days of therapy.Small epidemics of bubonic plague continue to occur in widespread regions of the world, including the United States. The epidemics fail to spread beyond local outbreaks, however, which may suggest that less virulent strains of the plague bacterium have developed over the years and conferred a relative immunity to many people. That plague does recur indicates its existence as a chronic disease among wild rodents. Bubonic plague will continue to inflict humans for a long time to come because of plague s presence in so many burrowing rodents. Sporadic human cases associated with wild rodents occur annually in the western United States. In 1992 human plague cases were reported in Brazil, China, Madagascar, Mongolia, Myanmar, Peru, the United States, Vietnam, and Zaire. Major outbreaks in India have occurred as late as 1994. As long as plague infested rodents can come into close contact with human habitats, outbreaks of bubonic plague will continue to appear across the world.