Plagues and History: From the Black Death to Alzheimer's Disease

Abstract

A broad chronological overview of the plagues of the past and the present provides a basis for understanding how they have arisen, how they have affected societies over time, and how humanity has responded to the challenge of each new wave of deadly disease. Many puzzles still surround the plagues of antiquity, although recent techniques such as DNA analysis of skeletal remains are beginning to provide clues as to their causes; it has, for example, now been confirmed that the plague bacillus, Yersinia pestis , was responsible for the ‘Black Death’ of the mid-14 th century. Many other infectious diseases or ‘plagues’, such as smallpox, typhus, cholera and influenza, have afflicted human populations over the centuries. As the causes of these diseases have become increasingly well understood, humanity has devised ever more effective means for their control. With the extension of human lifespan that has resulted from such progress, other medical conditions have become increasingly common, notably the neurological disorder, Alzheimer's disease. Although not infectious, this disease has become so prevalent in recent years that it is has been called a ‘21st century plague’. The intrinsic origins of this highly debilitating condition are now being explored intensively by scientists from many different disciplines leading, as with the plagues of the past, to new ideas as to potential strategies for its prevention and treatment. Most people associate the word ‘plague’ with the ‘Black Death’ of the mid-fourteenth century, which in the space of a few years killed between a third and a half of the population of Europe, Asia and the Middle East – with frightening consequences. However, throughout history there have been many other widespread and devastating outbreaks of disease that have been labelled as plagues. The word ‘plague’ comes from the Latin plaga , meaning a stroke or a wound; the Oxford English Dictionary also defines it as an affliction, calamity or a general name for any malignant diseases ‘with which men or beasts are stricken’. The word is, moreover, now becoming associated with some disorders that are not infectious, but which have increased in prevalence so rapidly that they have been likened to the historic plagues. One such condition in humans is dementia, which has been called the ‘twenty-first century plague’, and indeed it is perhaps as greatly feared today as the classic plagues were in the past.