1346-1353 spread of the Black Death in Europe map

Spread of the Black Death in Europe and the Near East (1346–1353).

The Black Death is a disease that spread through Europe. This disease wiped out 75-200 million people in Europe at the time because there was no current cure. This disease is also known as the Black Peague. The plague created a series of religious, social, and economic upheavals, which had profound effects on the course of European history. From there, it was most likely carried by Oriental rat fleas living on the black rats that were regular passengers on merchant ships, spreading throughout the Mediterranean and Europe. t took 200 years for the world population to recover to its previous level. The plague recurred as outbreaks in Europe until the 19th century. The bacterium Yersinia pestis, which results in several forms of plague, is believed to have been the cause. 

The plague disease, caused by Yersinia pestis, is enzootic (commonly present) in populations of fleas carried by ground rodents, including marmots, in various areas including Central Asia, Kurdistan, Western Asia, Northern India and Uganda. Due to climate change in Asia, rodents began to flee the dried out grasslands to more populated areas, spreading the disease. Nestorian graves dating to 1338–1339 near Lake Issyk Kul in Kyrgyzstan have inscriptions referring to plague and are thought by many epidemiologists to mark the outbreak of the epidemic, from which it could easily have spread to China and India. In October 2010, medical geneticists suggested that all three of the great waves of the plague originated in China. In China, the 13th-century Mongol conquest caused a decline in farming and trading. However, economic recovery had been observed at the beginning of the 14th century. In the 1330s, a large number of natural disasters and plagues led to widespread famine, starting in 1331, with a deadly plague arriving soon after. Epidemics that may have included plague killed an estimated 25 million Chinese and other Asians during the 15 years before it reached Constantinople in 1347.

The disease may have travelled along the Silk Road with Mongol armies and traders or it could have come via ship. By the end of 1346, reports of plague had reached the seaports of Europe: "India was depopulated, Tartary, Mesopotamia, Syria, Armenia were covered with dead bodies".

Plague was reportedly first introduced to Europe via Genoese traders at the port city of Kaffa in the Crimea in 1347. After a protracted siege, during which the Mongol army under Jani Beg was suffering from the disease, the army catapulted the infected corpses over the city walls of Kaffa to infect the inhabitants. The Genoese traders fled, taking the plague by ship into Sicily and the south of Europe, whence it spread north. Whether or not this hypothesis is accurate, it is clear that several existing conditions such as war, famine, and weather contributed to the severity of the Black Death. 

Medical knowledge had stagnated during the Middle Ages. The most authoritative account at the time came from the medical faculty in Paris in a report to the king of France that blamed the heavens, in the form of a conjunction of three planets in 1345 that caused a "great pestilence in the air". This report became the first and most widely circulated of a series of plague tracts that sought to give advice to sufferers. That the plague was caused by bad air became the most widely accepted theory. Today, this is known as the miasma theory. The word plague had no special significance at this time, and only the recurrence of outbreaks during the Middle Ages gave it the name that has become the medical term.

The importance of hygiene was recognised only in the nineteenth century; until then it was common that the streets were filthy, with live animals of all sorts around and human parasites abounding. A transmissible disease will spread easily in such conditions. One development as a result of the Black Death was the establishment of the idea of quarantine in Dubrovnik in 1377 after continuing outbreaks.

The dominant explanation for the Black Death is the plague theory, which attributes the outbreak to Yersinia pestis, also responsible for an epidemic that began in southern China in 1865, eventually spreading to India. The investigation of the pathogen that caused the 19th-century plague was begun by teams of scientists who visited Hong Kong in 1894, among whom was the French-Swiss bacteriologist Alexandre Yersin, after whom the pathogen was named Yersinia pestis.The mechanism by which Y. pestis was usually transmitted was established in 1898 by Paul-Louis Simond and was found to involve the bites of fleas whose midguts had become obstructed by replicating Y. pestis several days after feeding on an infected host. This blockage results in starvation and aggressive feeding behaviour by the fleas, which repeatedly attempt to clear their blockage by regurgitation, resulting in thousands of plague bacteria being flushed into the feeding site, infecting the host. The bubonic plague mechanism was also dependent on two populations of rodents: one resistant to the disease, which act as hosts, keeping the disease endemic, and a second that lack resistance. When the second population dies, the fleas move on to other hosts, including people, thus creating a human epidemic.

The historian Francis Aidan Gasquet wrote about the Great Pestilence in 1893 and suggested that "it would appear to be some form of the ordinary Eastern or bubonic plague". He was able to adopt the epidemiology of the bubonic plague for the Black Death for the second edition in 1908, implicating rats and fleas in the process, and his interpretation was widely accepted for other ancient and medieval epidemics, such as the Justinian plague that was prevalent in the Eastern Roman Empire from 541 to 700 CE.

An estimate of the mortality rate for the modern bubonic plague, following the introduction of antibiotics, is 11%, although it may be higher in underdeveloped regions. Symptoms of the disease include fever of 38–41 °C (100–106 °F), headaches, painful aching joints, nausea and vomiting, and a general feeling of malaise. Left untreated, of those that contract the bubonic plague, 80 per cent die within eight days.Pneumonic plague has a mortality rate of 90 to 95 per cent. Symptoms include fever, cough, and blood-tinged sputum. As the disease progresses, sputum becomes free-flowing and bright red. Septicemic plague is the least common of the three forms, with a mortality rate near 100%. Symptoms are high fevers and purple skin patches (purpura due to disseminated intravascular coagulation). In cases of pneumonic and particularly septicemic plague, the progress of the disease is so rapid that there would often be no time for the development of the enlarged lymph nodes that were noted as buboes.

A number of alternative theories – implicating other diseases in the Black Death pandemic – have also been proposed by some modern scientists (see below – "Alternative Explanations").

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