The Dissemination of Disease Within East Asia

By late Han times Chinese culture began to spread to the other regions of East Asia. As the indigenous peoples of Korea and Japan began to adopt irrigated, wet-rice agriculture, their numbers increased, cities were built, and these countries began to be afflicted with the civilized diseases of China. Contact between China, Korea, and Japan increased after the sixth century, and smallpox and other epidemic diseases were spread along with Buddhism and other cultural exports.

Japanese accounts of smallpox epidemics in A.D. 585 and 735-7 provide excellent early descriptions of this disease. The smallpox epidemic of 735 came from the kingdom of Silla in southern Korea. It began in the part of Kyushu nearest to Korea, and it spread toward the major population centers in the region around the capital at Nara. Although this was not Japan's first smallpox epidemic, it caused high mortality among all age groups in the population, indicating that smallpox epidemics did not reach Japan very frequently. Wayne Farris believes that high mortality from virulent, imported diseases between 645 and 900 caused Japan to suffer a demographic setback that had a major impact on Japan's political, economic, and social development in this early period.

Once imported epidemics reached Japan, the direction of spread was invariably from the southwest — where ports of entry for foreign ships were located - to the northeast along routes where Japan's population was concentrated. Japan had a high population density very early in its history, and as in China, most diseases became endemic with little difficulty. Smallpox was clearly endemic in Japan by the twelfth century and probably well before (Jannetta 1987).

The more sparsely settled and remote areas of East Asia could still be seriously threatened by severe epidemics as late as the seventeenth century. In Japan, offshore islands, villages in the northeast, and mountainous regions remained vulnerable. In China it was the dispersed, low-density populations that lived in semiautonomous areas along the enormous northern and western frontier that were at greatest risk of suffering highly disruptive mortality from epidemics.

During the seventeenth and eighteenth centuries, the dissemination of disease intensified as these peripheral regions were gradually incorporated into the main networks that operated in East Asia. Several factors contributed to this intensification process: East Asian populations increased in size and density, urbanization accelerated in both China and Japan, contact between core and periphery increased, and activity on China's frontier intensified.

Changes in tribute relations accompanied the consolidation of Tokugawa and Ch'ing power in the sev enteenth century, and promoted the dissemination of disease within East Asia. Between 1637 and 1765, contacts between China and Korea increased: An average of 3.8 tribute missions a year traveled from Korea to Peking, and in fact Korea and the Ryukyu Islands sent tribute missions to Japan as well. The King of the Ryukyus was regularly required to pay his respects to the daimyo of Satsuma and on occasion to the Tokugawa shogun in Edo (Sakai 1968). In Japan, the shogunate institutionalized contact between core and periphery with the creation of the sankin-kotai system. This system required that large numbers of retainers travel to Edo from each of the provinces in alternate years to pay attendance upon the shogun. All of these activities would have increased the rate of disease dissemination in Japan.

The development of interregional trade in Japan also served to disseminate density-dependent diseases throughout the islands. As outlying regions were drawn into a more widespread market network, they were also incorporated into a wider network of disease dissemination. Local records show that epidemics became more frequent in the hinterlands of Japan during the Tokugawa period. By the end of the seventeenth century, smallpox epidemics were occurring every few years in outlying villages; by the end of the eighteenth century, smallpox epidemics had become increasingly frequent on the island of Tanegashima, and in the Ryukyu Islands. Even the most isolated islands of the Izu chain south of Chiba Prefecture were stricken by smallpox -reportedly for the first time - in the late eighteenth century. By the late 1700s density-dependent diseases common to the urban centers were afflicting even the most remote regions of Japan (Jannetta 1987).

On the East Asian mainland, the disease ecology of China began to expand across the northern frontier. To the north and northwest the range of Chinese expansion had been sharply limited. The steppes of Mongolia and Manchuria and the high Tibetan wastes had no great river systems from which water could be drawn to support intensive, irrigated agriculture, and a pastoral society that stood in stark contrast to that of China had developed on China's northern frontier. The steppe had become the home of nomadic tribes whose wealth was moveable herds of livestock, not land or grain. The Great Wall of China, built to keep out the "barbarian" peoples who raided Chinese settlements, marked the frontier between two fundamentally different cultures.

The Great Wall also marks the frontier between the two major disease ecologies of East Asia. The dispersed and mobile populations north of the Great Wall had much less exposure to human pathogens than did the densely settled populations to the south. And because of infrequent exposure they were extremely vulnerable to the civilized diseases of China.

During the late Ming (1368-1644) and early Ch'ing (1644-1911) dynasties, Chinese civilization began to encroach on territories to the north, and there was increasing contact between northern Chinese and the nomadic peoples of the steppe. China's traditional policy had been to forbid trade with these barbarian enemies. But as this policy simply encouraged invasion raids and seizure of whatever goods were available, at times the Chinese government reluctantly set up official markets to facilitate the exchange of goods.

The numerous military campaigns of the late Ming period required large supplies of horses. In the second half of the sixteenth century, the Chinese set up official horse markets on China's northern frontier, where cloth and grain were exchanged for Mongol cattle, sheep, mules, and horses. Initially there were four market locations - at Tatung, Hsuan-fu, Yen-sui, and Ningsia - where horse fairs were held during the spring and summer months. In time, smaller markets were added at other places along the Great Wall where forts were situated. These small markets permitted Mongols who lived near the frontier to come to trade once or twice a month, and the regularization of these markets provided a more dependable supply of goods for Chinese and Mongol alike (Hou 1956). At the same time, more frequent contact between Mongols and Chinese permitted the dissemination of the density-dependent diseases of China to the tribal peoples of the steppe.

The disease problems that followed the growth of fairs and the border trade in the second half of the sixteenth century are documented in both Chinese and Mongol sources. The Mongols were most fearful of smallpox, which was rare in Mongolia. The biography of Tu T'ung, a military commander in Shensi, tells of an incident in which men returning from the border caught smallpox and died. The incident resulted in several border clashes, because the Mongols, who were unfamiliar with smallpox, thought that the men had been poisoned by the Chinese.

Chinese contacts constituted the gravest danger from smallpox for the Mongols, who recognized that danger and did what they could to contain the disease and prevent further contamination. It was customary strictly to avoid the stricken person, whether a parent, brother, wife, or child:

They provide [the sick] with a Chinese to take care of him; and if there is no Chinese available, they prepare his food and other necessities in a place other than their own and let the person stricken with smallpox take care of himself. . .. [TJhey regard China as a house on fire, and they refuse to stay there long for fear of contracting smallpox. (Serruys 1980)

For the Mongols the danger of exposure to smallpox and other diseases increased during the sixteenth century because of increasing contact with the Chinese. Not only did they encounter them during invasion raids and at the border markets and fairs, but also after midcentury many Chinese immigrants settled north of the Great Wall and lived intermingled with the Mongols. These communities were particularly vulnerable to high mortality from epidemic diseases. One Chinese observer claimed that the border communities had grown to 100,000 by the 1590s, but "luckily" a great epidemic had cut their numbers down by half (Serruys 1980).

The Manchus, too, had increasing problems with the civilized diseases of China. In Manchuria, as in Mongolia, smallpox was a relatively rare disease. The widely scattered populations, often on the move, had prevented the virus from gaining a foothold. However, in the late Ming as Chinese began to settle in Manchuria and as contacts between Manchus and Chinese increased, the diseases of China - smallpox in particular - became a serious threat.

An observation relating to the year 1633, when the Manchu armies were ready to invade China, indicates their awareness of this threat: "Order beiles who have already once contracted smallpox to lead an army from I-p'ien-shih to take Shan-hai-kuan" (Serruys 1980). The order to pick only immunized troops for an extended stay in China shows that they understood the great risk of contracting smallpox there, and they knew that those who had once had the disease would not get it again.

Even after China was conquered by the Manchus, Ch'ing legislation for the Mongol bannermen indicates that the Manchu rulers continued to take the problem of smallpox seriously. Proscriptions against going to the capital when one had not been already infected with the disease were incorporated into the Ch'ing codes. Two expressions - "those who have already had smallpox" and "those who have not yet had smallpox" - became almost technical terms in the Li-fan-yuan code, which was translated into Mongolian. Mongols who inherited a rank within the administration, and who would normally go to Peking to receive their succession, were excused if they had not yet contracted smallpox. They would go in stead to Jehol for the ceremony. Although some scholars have thought that the code was designed to protect the Chinese from Mongol infections, it is clear that its intent was to protect the Mongols who would needlessly be exposed to a grave danger.

These examples illustrate the changes that took place in East Asia in the early modern period. There were real differences between the disease ecologies of the East and West, and these differences continued to be important. Unlike Africa, the Americas, and many of the more sparsely settled countries of Europe, many density-dependent diseases were already endemic in East Asia before the sixteenth century. Disease ecologies in the West were completely transformed by the discovery of the New World. The high level of epidemic mortality in the early modern West may well be related to the unusual disease exchange that took place between the urban centers of Europe and the peripheral primitive societies with relatively low-density populations with which they came in contact.

No such transformation took place in East Asia. There was much greater stability in the high-density populations of China and Japan where many diseases were endemic and circulated regularly within a relatively closed system. Thus the arrival of the Europeans in the sixteenth century changed the disease ecology of East Asia very little.

The disease environment of early modern East Asia did change, but the reason for change was totally unrelated to new foreign contacts. In East Asia the dissemination of disease intensified because of population growth, increasing urbanization, an increase in the volume of trade within the region, and the integration of more sparsely populated frontier regions into the network of civilized diseases. This process was affected very little by outside developments. In the modern period, however, when rapid transport began to connect all of the world regions, East Asia's large, high-density population emerged as a disease center that could disseminate diseases to the rest of the world.

Ann Bowman Jannetta

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