The diseases of early modem Japan (the Tokugawa period) are of particular interest to the history and geography of disease.
The Japanese Islands, situated as they are at the far eastern periphery of East Asia, had relatively little contact with the people of other world regions until the late nineteenth century.
Historically Japan’s isolation afforded the people some measure of protection from exposure to certain of the world’s diseases, and in the early seventeenth century, the Tokugawa shoguns reinforced this natural protection when they imposed severe restrictions on foreign contacts. They limited official foreign trade to the port of Nagasaki, restricted the number and the nationality of ships that could enter that port, denied mobility beyond the port to the crews of foreign ships, and prohibited the Japanese from going abroad and returning to Japan. These policies were a response, in part, to the unwelcome activities of Westerners who had begun to reach the islands in the second half of the sixteenth century. They remained in effect until a U.S. fleet forced Japan to open its ports to international commerce in the 1850s.Elsewhere explorers, adventurers, traders, and settlers were circumnavigating the globe, carrying new diseases to previously unexposed peoples, and causing waves of high mortality among the populations of many world regions. By 1850 the increasing volume of international contacts had produced a worldwide system of disease dissemination, but Japan, remaining aloof from world affairs, had also remained largely unaffected by the epidemiological events of the early modem world. The diseases of Tokugawa Japan were, for the most part, diseases that had reached the islands centuries earlier.
Japan was part of an East Asian disease dissemination system that differed in certain respects from that of western Eurasia. Human populations in East Asia were larger and more dense than those in the West, and many human disease organisms were able to establish permanent reservoirs of infection with little difficulty.
In earlier times, epidemic diseases were disseminated outward from the large population centers of China to the less densely settled regions of the periphery. Occasionally these epidemics would reach Japan, and Japan’s population, which was heavily concentrated along the coastal plains, provided an environment highly conducive to disease propagation and dissemination. By 1600, Japan’s population was large enough to support many disease organisms in endemic fashion that in earlier times had been imported as epidemics from China.The most important changes in the disease environment of early modem Japan, relative to earlier periods, were brought about by domestic rather than international developments. Japan’s population grew from about 18 million to approximately 30 million people during the seventeenth century, and Edo (present-day Tokyo) became one of the world’s largest cities with a population of around 1 million inhabitants. Economic development, which included the commercialization of agriculture, regional specialization, and interregional trade, accompanied population growth. All these developments served to intensify disease transmission within Japan, and by 1850 few communities were remote enough to avoid either the indigenous diseases of Japan or the imported diseases that sometimes managed to penetrate the cordon sanitaire that served to protect the country from the international traffic in pathogens.