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37 Three The Great Plague Pandemic The most serious epidemic outbreak in Western history began in Sicily in October 1347. Between that date and the end of 1353 most of Europe was affected. The disease most likely responsible was the plague, apparently in both its bubonic and its pneumonic forms. In the course of this massive epidemic between 30 and 60 percent of Europe’s population died, a nearly inconceivable human disaster. The event—much later and for unclear reasons called the Black Death— had a profound impact on the imagination of the time, and has attracted considerable historical attention in recent decades. What caused the epidemic? Where did it come from? Where it go, and how did it spread? Was the Western society of the 1340s ripe for such a catastrophe? What did medieval people make of the epidemic? What did they do about it? What were its consequences? And finally, why and when did plague cease its hold on the West? All these questions have generated historical controversy and will repay careful review. Plague Plague is caused by a microorganism, Yersinia pestis (or as it was formerly known, Pasteurella pestis), parasitic in various burrowing rodents. The microorganism is carried from rodent to rodent most frequently by fleas, which bite infected rodents and then carry the bacteria to other rodents. Many rodents may carry plague, including marmots, ground squirrels, and prairie dogs, but the rodent most often involved with human epidemics has been the rat, and especially the so-called black rat (Rattus rattus), an adept climber that is particularly at home in human dwellings. Plague may remain enzootic (that is, endemic among animals) in a population of rodents for a long time. If it reaches epizootic intensity (that is, becomes epidemic) the larger number of animal deaths will increase the number of their accompanying fleas who will seek new hosts. Those fleas may become vectors—carriers that convey an infectious agent from one host to another. In the case of the black rat, the rat flea (Xenopsylla cheopis) is a frequent vector, but other flea species may play a role, including (although this is controversial) the human flea (Pulex irritans). The new host may—perhaps only by chance—be a human. When a flea transmits the microorganism to a human, the form of plague called “bubonic” results, a disease that apparently depends on a continuing epizootic of infected rodents during which humans inadvertently get in the path of a rodent- flea-rodent transmission. Plague may, however, pass from one human to another. Some authorities believe that the human flea, Pulex irritans, sometimes carries Yersinia pestis bacilli between people, making the spread of bubonic plague possible without the constant necessity of an epizootic rodent reservoir. And all agree that the pneumonic form of plague requires no vector. Pneumonic plague occurs when Yersinia pestis settles in the lungs, and from there spreads by drops of saliva into the respiratory tracts of others. Pneumonic plague was almost certainly an important element in the great epidemic that began in 1347, but the fact that it is almost invariably and rapidly fatal limits its power of diffusion, for its victims perish before they travel far or contact many others. Many questions persist about the identification of the microbe responsible for the great “plague” of 1347–1353. Some of those questions focus on its apparent epidemiology. How could an epidemic on the scale of the 1347–1353 events be generated by accidental encounters with fleas that generally have little interest in human hosts? How could the epidemic spread so rapidly across a subcontinent when it depended on populations of infected rodents that move from place to place only very slowly? To drive so many fleas to seek human hosts, rats must have died in immense numbers; why didn’t contemporaries notice an unusual pile of dead rats? On the basis of such questions some biologists, epidemiologists , and historians have argued either that the disease of those years cannot have been plague, or that (if it was plague) the generally accepted mortality figures must be highly exaggerated.1 Such arguments, however persuasive, fly in the face of considerable historical documentation of both the extent of the disaster and the symptoms of the disease . Bubonic plague manifests itself most dramatically in “buboes,” the large, hard, painful swellings in the groin, armpit, or neck that form when the infection reaches the lymphatic system. Devastating symptoms rapidly ensue: a rapid rise of body temperature, delirium for some...

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