In the Japanese archipelago, smallpox unfolded a very diverse epidemiological landscape. In some areas, the epidemic occurred once every few decades and caused devastating damage, while in others, it was year-round and attacked only children. In the face of this mysterious phenomenon, people in each era developed their own theories on the causes of the epidemic and ways to deal with it. This paper reviews the history of such etiologies and coping strategies prior to the widespread use of vaccination in modern times.

Introduction: The historical perception of epidemics—how infectious diseases have been defined and dealt with

The phenomenon in which members of a population all fall ill at once has been seen time and time again throughout history, and the Japanese archipelago is no exception. Historical records dating back to antiquity prove that this bow-shaped island chain to the east of mainland China has indeed been the site of outbreaks of infectious diseases. In the Nihon shoki (日本書紀), Japan's oldest officially compiled history, the following is recorded to have taken place in the year Sujin 5 (Estimated circa 1st century B.C.), during the tenth Emperor's reign. “The disease spread throughout the country, taking people's lives, and the greater part of the population at that.” To have suffered an epidemic of such proportions must have been catastrophic for the nascent country.

What could cause a large number of people to suffer from the same afflictions at the same time? Ancient people believed the spread of epidemic diseases to be a supernatural phenomenon and so tried to suppress them by calling upon the power of divine spirits. Given their circumstances, this was the most “rational” way to approach the situation.

How we deal with infectious diseases is always informed by how we define them. In the 21st century, we understand the spread of infectious diseases as a chain reaction that starts with a physical pathogen entering the human body, causing it to suffer various symptoms. Measures are taken accordingly: we remove disease-causing pathogens through disinfection and sterilization, we halt the spread of disease through quarantine and travel-related control measures, and we develop our immunities against disease (whenever possible, through vaccination) to prevent infection.