The Black Death of the Middle Ages has long held a mythic place in history as a story of a terrible pestilence visited upon Europe, a pestilence that perhaps could return one day. Yet, in the modern age we have been able to control most infectious diseases, eliminating the unsanitary conditions that produce them in the industrialized nations and attacking them with wonder drugs in areas still afflicted with such problems. In the fourteenth and fifteenth centuries, the Black Death decimated Europe and caused massive economic and social damage to the nations of Europe.
The organism that causes bubonic plague is well known today. The plague is caused by a bacillus called Yersinia pestis that is transmitted by the flea. Plague is primarily a disease of rodents, and epidemics with human begins begin with contact with the fleas of infected rodents. The two primary forms of the disease in the human being are the bubonic plague, the most common form in the Middle Ages, and which is characterized by the swelling of the lymph nodes, and pneumonic plague, with the extensive involvement of the lungs. Plague is spread from rodents to human beings in crowded urban areas. In the fourteenth century, the disease was known as the Black Death, and some plague infections were bubonic and some were pneumonic. It has been estimated that in various parts of Europe between two-thirds and three-fourths of the population was killed in the first pestilence, and one-quarter of the population of all of Europe may have died during the great epidemic (Duiker and Spielvogel 488-489).
Some historians believe that the population had been weakened even before the advent of the plague because of famine:
. . . famine could have led to chronic malnutrition, which in turn contributed to increased infant mortality, lower birthrates, and higher susceptibility to disease since malnourished people are less able to resist infection (Duiker and Spielvogel 488).