Smallpox in history: the birth, death, and impact of a dread disease.

S mallpox, despite its savage effects, is a disease of civilization. It could hardly be otherwise. A virus that has only human hosts, that produces an acute disease of relatively short duration and leaves behind among the living only individuals with robust immunity and no chronic carriers could hardly have survived until large settled human communities appeared after the invention of horticulture and the domestication of animals. These altered conditions for human life probably permitted a pox virus of herd animals to find human beings a suitable host and to move from host to host in a timely fashion. The slim evidence that we possess from early human history, three Egyptian mummies showing suspicious eruptions of the skin and the more ambiguous testimony of early texts describing disease outbreaks, is consistent with this theory and suggests that smallpox spread from Egypt and Mesopotamia to India and China. We do know with much greater certainty that smallpox was endemic in all of these ancient cradles of civilization by the second century AD. Northern Europe’s experience with smallpox was delayed until the 11th and 12th centuries, when the Crusades and expanding trade gave Europeans more regular contact with the virus. By the 15th century, smallpox was endemic in Northern Europe, and by the 17th it had replaced bubonic plague as Europe’s most feared pestilence. Like plague, it had great political significance. In 1694, Queen Mary of England died of smallpox, and six years later her son, the Duke of Gloucestershire, also died of the disease. His death resulted in a constitutional crisis because he was the only heir to the throne. During the 18th century, the royal families of Europe continued to suffer along with their subjects. In the 80 years after Mary’s death, smallpox carried off Emperor Joseph I of Austria, King Luis I of Spain, Tsar Peter II of Russia, Queen Ulrika Eleonora of Sweden, and the French King Louis XV. In Western nations, smallpox was a constant threat to life. It killed an estimated 400,000 Europeans each year by the late 18th century, and it ensured that only the rare adult had an unblemished complexion. During this period, Europeans’ experience with smallpox depended in large measure on the type of community in which they resided. In the largest capital cities—London or Paris, for example—smallpox was endemic, and residents experienced the disease as a deadly affliction of young children and recent arrivals from the country that took some victims year after year and occasionally flared up to kill larger numbers. In provincial towns too small for the smallpox virus to find a continuous string of susceptible hosts, smallpox appeared only at intervals, causing explosive epidemics that included children of all ages, as well as some adults (Fig 1). Boston’s experience was like that of many English provincial towns. Its small size and isolation from endemic centers and a policy of isolating imported cases shielded it from infection for years at a time, but smallpox, when it was imported and found a large enough pool of nonimmunes, caused major outbreaks in 1721, 1730, 1752, 1764, 1776, 1778, and 1792. Outbreaks such as these were limited by the herd immunity acquired in previous epidemics. However, when the smallpox virus was introduced into a population that had no acquired immunity, a demographic catastrophe was possible. We can only imagine what happened as smallpox spread to new territories in Asia From the Program in the History of Medicine, University of Minnesota.