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The Bubonic Plagues
From: Cambridge University Press
| By:
Ernest Zebrowski, Jr. |
EDITOR'S INTRODUCTION |
In the first month of the second millennium, a New Mexico woman contracted plague. Infected house mice were identified as the source. The woman recovered in hospital, but had she lived in medieval Europe, her plight would most likely have been death. In this extract from Perils of a Restless Planet, Ernest Zebrowski, Jr., vividly revisits the lurking bacillus that claimed victims in all of Europe's cities between the sixth and seventeenth centuries. |
 efore the rise of modern sanitation and medicine, cities were the unhealthiest places anyone could possibly choose to live. Until the early 1800s, the death rate exceeded the birth rate in almost every large city in the world. The only way cities managed to sustain their populations during most of human history was by attracting immigration at a rate that compensated for the excessive urban death rates. Some cities, of course, failed to do this and are today populated only by archaeologists. |
Naturally, humans would not have flocked to these death traps if there had not been seductive reasons to do so. The attractions were, in virtually all cases, economic: Cities offered employment opportunities and cultural trappings--that is, wealth and prosperity. Cities generated their wealth not by becoming microcosms unto themselves but rather by trading regularly with networks of other cities. Thus evolved an expanding web of trade routes that had the unanticipated consequence of greatly enhancing the opportunities for microbes to infect new populations of densely packed human hosts. |
The rise of cities provided human microparasites a new and wonderful ecological niche. Although the evolution of many new human diseases was driven in this manner by the rise of cities, certainly the most terrible to date has been deadly bubonic plague. The most serious outbreaks of this devastating disease occurred in the sixth, fourteenth, and seventeenth centuries, and these three epidemics alone may have killed a total of some 137 million Europeans, in addition to unknown but certainly large numbers of Asians. |
The rat factor
The agent of bubonic plague is the bacillus Yersinia pestis, which seems to have had at least two natural animal hosts for many thousands of years before human cities arose on the planet. One of these hosts is the common black rat Rattus rattus, also known as the house rat, ship rat, or river rat. Another host is the rat flea Xenopsylla cheopis, which derives its nourishment by sucking the blood of the black rat. The bacillus multiplies in the bloodstream of an infected rat, eventually infecting the rat's lungs or nervous system and ultimately causing a convulsive death. Until very near its demise, however, the rat tolerates the infection fairly well (maybe even for a year or so), and in this time there is ample opportunity to produce several generations of baby rats. Meanwhile, the rat flea can also tolerate up to a few hundred thousand bacilli in its gut before it begins to regurgitate the bacillus as it tries to feed. Before the bacillus kills a typical rat flea, this tiny insect also has a chance to produce multiple generations of baby fleas. |
Before an infected rat dies, the bacillus population in its blood grows so dramatically that no flea on its body can escape infection. When the rat does die, these fleas (which are very sensitive to temperature changes) immediately desert their dead host and look for a new source of nourishment. Although a flea will eat daily if a host is available, it can live for as long as two weeks without eating. In this period, there is a high probability that an infected flea will find a new rat, which, at least eventually, it will infect with the plague bacillus. In this manner, the bacillus is passed back and forth from rat to flea, flea to rat, generation after generation, in an essentially closed community. Some scientists have suggested that this process may have gone on for as long as 1 million years before the first human epidemic of bubonic plague. |
We don't know for sure when the bacillus first jumped species and mutated into a strain that could infect humans. A strange epidemic which bore some similarities to bubonic plague swept Athens around 430 B.C., and shortly after A.D. 300 a similar but more severe outbreak killed hundreds of thousands in Rome. Then in A.D. 540 came the great Plague of Justinian, which contemporaries documented well enough to leave little doubt today that this was indeed an outbreak of bubonic plague. This epidemic originated in lower Egypt, moved north to Alexandria on the Mediterranean coast, from there traveled to Palestine, then spread to Constantinople (which at that time was the capital of the Roman Empire), clearly following the major trade routes. |
When, in 541, the emperor Justinian returned to his capital from his unsuccessful war in Persia, he found to his horror that his subjects were dying at the rate of up to 10,000 per day. Because even mass graves could not be dug fast enough, Justinian ordered that the roofs be removed from the towers of the city walls to provide places to efficiently stack the corpses; soldiers then poured lye onto these tall piles of bodies to hasten their decomposition. Even this drastic measure, however, was insufficient to dispose of the huge numbers of people who were dying. Eventually all of the city towers were filled with decaying bodies, and the dead had to be loaded into ships, which were then taken to sea and set ablaze. Justinian himself was struck by the disease, and his wife Theodora reigned during his illness. Although he recovered, Justinian never regained his full physical strength and was left with a speech defect for life. By 542, the lives of 40% of the inhabitants of the great city of Constantinople had been claimed by the epidemic, and in fact this may have been the ultimate blow that led to the downfall of the Roman Empire in the Middle East. Meanwhile, the plague did not stop at Constantinople but continued to spread northward and westward, gradually decreasing in intensity until around 590, when apparently the last cases were reported. By that time, the epidemic had destroyed the critical mass of population it needed to sustain itself as a human disease. |
This plague was much more lethal to humans than it had been to either rats or fleas, a common characteristic of diseases that jump species. The bacillus had also found new ways to transmit itself directly from person to person, without the need to depend on a flea as an intermediary. The combination of these two factors allowed the bacillus to destroy the very environmental conditions that had contributed to its own population explosion. It was so successful in multiplying, and so lethal to its human hosts, that it put itself out of business. |
Three modes of attack
Although no one would recognize this fact for many centuries, there were three different ways the plague could attack its victims. One was the injection of the bacillus into the blood by the bite of the flea. In this case, a few days would pass before the first symptoms of aches, chills, confusion, and fatigue. Then purple splotches began appearing on the skin, followed by heart flutters, a collapse of the nervous system accompanied by dreadful pain, a brief stage of wild anxiety and terror (sometimes resulting in the so-called "dance of death"), then often death itself. This sequence of symptoms typically took five to seven days. Recovery, however, was not impossible, and, if it happened, the victim was immune from a recurrence for life. |
A second form of the disease (which in fact may have been the most common) was pneumonic, where the bacillus was transmitted directly from person to person through the air. Again the incubation period was two to three days, then came a severe bloody cough and death within the next few days. This form of the disease seems to have been fatal in at least 19 of 20 cases. In the third form, an insect bite immediately triggered a violent septicemic reaction by the body, and the victim invariably died the same day (and perhaps within a few hours), before any major visible symptoms appeared. This third course of the disease is still not well understood, and in fact there may have been a carrier other than the rat flea involved here (perhaps a mosquito transferring the bacillus directly from human to human). The contemporary accounts suggest that no one ever survived septocemic plague. |
In 1345, eight centuries after the Plague of Justinian, reports began arriving in Europe of a fearful pestilence in the Far East. The next year, as millions were dying in India, this plague expanded along the established trade routes to the West. According to contemporary accounts, the epidemic first entered Europe on a Genoese ship that sailed from the Crimea to the Sicilian port of Messina and docked there in 1347 with a crew of sick and dying sailors. When the disease began spreading into their city, the residents of Messina (much too late to have any effect on their own outbreak of the plague) drove all of the foreign ships back out to sea--eventually to dock elsewhere and accelerate the spread of the epidemic. By the end of the year, the epidemic had spread into northern Italy. By June of 1348, it had engulfed all of Italy, most of France, and the eastern part of Spain. Six months later, it appeared in southern England and Germany. By June of 1349, it had progressed deeper into England, appeared in southern Ireland, engulfed all of France, and was expanding farther into Germany. By the end of 1349, Denmark and Scotland felt its effects. In 1350, the epidemic spread eastward through Scandinavia. Although people living in the countrysides of Europe were often spared, the cities were devastated. Overall, the plague killed roughly one-third of the Europeans alive in 1347. |
For city after city, we find gruesome accounts describing the huge number of corpses, the problems of their disposal, and the psychological impact on the survivors. The bubonic plague was by far the most lethal natural disaster of the Middle Ages. This epidemic claimed many times the number of lives of the earlier Plague of Justinian, simply because by 1347 there were many more pockets of high population density where the bacillus could afford the luxury of killing its hosts and still have other hosts to move on to. In 1351, the Vatican estimated that the plague had already claimed 24 million European lives; it is likely that an additional 20 million died before the European branch of the epidemic ran its course around the end of that century. Meanwhile, the death toll in the Middle East and Asia was probably higher. Curiously spared, however, was most of Poland. This stroke of good fortune played no small part in that nation's emergence as a major cultural and political power in the late 1300s, a role that it played on the stage of European history for the next two centuries. |
Conclusion
The great plague killed much more efficiently than any war humankind has ever known, and it might seem that this high morbidity would have drastically reversed the world's population growth curve. In fact, however, the net population growth rate seems to have been negative for only a few years as the plague swept through. Within two generations after the plague, the world's population count had grown beyond its preplague level; in the six hundred years since then, the world's population has never had another interval of net decline, not even during the two world wars of the twentieth century. |
Many contemporary theories arose for the cause of bubonic plague, most drawing upon supernatural or astrological explanations. If anyone indeed proposed that rats and fleas were involved, the proposal apparently wasn't taken seriously. Microorganisms, of course, were unknown in the fourteenth century, so there was no way a complete theory of the epidemic could possibly have been developed at that time. |
A little more than two centuries later, in 1665-6, bubonic plague emerged again in western Europe. In London, where this epidemic peaked in the summer of 1665, 2,000 people died each week. This time, however, the plague did not spread as widely, nor was it as lethal. The trend toward less virulent outbreaks of more limited scope has continued ever since: The San Francisco bubonic plague epidemic of 1907, for instance, had 160 documented cases and 77 deaths (and this before antibiotic treatments were developed). Today, in a typical year a few hundred cases will be reported worldwide, with a mortality rate that now hovers around 3%. This suggests that the bacillus has evolved into a form where it is again in relative equilibrium with its global environment, of which human populations have become one integral part. |
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