Infectious Diseases
Smallpox
Among the acute infectious diseases that can be clearly identified from the sources, smallpox emerges as the major killer and the most common cause of premature death.
Certainly, more medical books were written about this illness than any other. An old disease in Japan, smallpox was endemic in the large cities well before 1600, and by the late eighteenth and early nineteenth centuries, epidemics struck even remote parts of Japan every 3 or 4 years. Smallpox was almost entirely an illness of children under the age of 5 years, with few escaping it and many dying of it. As late as 1850, at least 10 percent of the population died of smallpox, and Western observers wrote in the 1860s that smallpox in Japan was so common that virtually every countenance was pockmarked. The introduction of smallpox vaccine in 1849 would reduce the importance of the disease as a cause of death by the late nineteenth century.Measles
The history of measles in Japan is unlike that of western Europe. In the parts of Europe for which there are good records, measles epidemics were reported frequently. At the end of the eighteenth century, for example, epidemics were occurring regularly in England in about one of every 3 years, and in Germany at regular intervals of about 4 to 5 years. But in Japan, only 11 measles epidemics were reported between 1616 and 1862, and contemporary accounts also provide evidence that epidemics were very rare. Consequently, measles was regarded as a dread disease because unlike smallpox, which was omnipresent, measles seemed to come out of nowhere, and infected young and old alike.
The different epidemiological patterns of measles epidemics in Japan on the one hand and in western Europe on the other seem to be related to different patterns of contact between populations in which the virus circulated. Frequent contact between the many trading centers of western Europe promoted the dissemination of the virulent measles virus and caused frequent epidemics.
By contrast, the restriction of trade and the infrequent and seasonal pattern of maritime trade between Japan and other countries of East Asia may have prevented the measles virus from being imported very often.In Japan the measles virus invariably spread from the port of Nagasaki in the southeast to the major cities of Kyoto, Osaka, and Edo to the northeast, and from there to the more remote parts of central and northern Japan. Moreover, it spread very rapidly because the population was densely concentrated along internal trade routes, and because, with infrequent epidemics, an unusually large segment of the population was susceptible to infection. In these circumstances, the measles virus quickly ran out of new hosts to infect and thus died out, which meant that a new importation of the virus was required for another epidemic to occur.
Unusually good records of measles epidemics were kept during the Tokugawa period, presumably because they infected so many people. These records document epidemics in 1616,1649,1690,1708,1730, 1753, 1776, 1803, 1824, 1836, and 1862. The geographic pattern of dissemination, the age distribution of the cases, and other contemporary evidence suggest that measles remained an imported disease that caused infrequent but severe epidemics in Japan until after 1850.
Measles was clearly distinguished from smallpox in the Japanese records because of its very different epidemiological pattern. A person was most likely to get smallpox as a young child because the virus was always circulating through the population, whereas a person would get measles only when the virus happened to sweep through the country. Morbidity and mortality rates were high in measles epidemics because of the large proportion of the population that became ill at once. However, measles mortality over the long term was much lower than smallpox mortality.
Other Airborne Infections
Other well-known airborne infections that cause skin rashes or eruptions are also described in Tokugawa sources.
Chickenpox, for example, seems to have been common. In fact, in the shogun’s palace, special ceremonies were held to celebrate a child’s recovery from smallpox, measles, and chickenpox, indicating that all of these diseases were considered a threat to life in Tokugawa Japan.Influenza is also prominently mentioned in the Japanese sources from early times, and 27 influenza epidemics are described in contemporary accounts of the Tokugawa period. The Japanese accounts are similar to accounts of influenza epidemics elsewhere: They describe a coughing epidemic that spread extremely rapidly, infecting everyone - young and old, male and female. As is typical of influenza, the mortality rate was highest among the very young and the very old. Influenza epidemics, like other imported epidemics, were said to enter Japan through the port OfNagasaki. In the seventeenth and eighteenth centuries, the timing of epidemics was different from those reported in Europe; but by the nineteenth century, influenza epidemics were noted in both regions at very nearly the same time. It appears that two distinct regional dissemination systems for influenza may have merged during the early modern period as the frequency of contact and speed of transport between East and West increased.
Diarrheal Diseases
In Japan, epidemics of diarrheal diseases were reported as early as the ninth century, but severe, large-scale epidemics seem to have been fairly rare in the early modern period. Fujikawa mentions only seven epidemics of diarrheal diseases for the Tokugawa period in his chronology of epidemics in Japan. It is impossible to distinguish between the different kinds of enteric diseases known today, because the symptoms of diarrheal infections are much the same regardless of the infecting agent. Such infections were most likely to be reported in Japanese historical sources when a large city or an important person was stricken, and these occasions were quite rare.
The absence of major dysentery-type epidemics is not too surprising.
Because enteric diseases are caused by contaminated water or food, they normally have a local or at most a regional distribution. Local records, however, suggest that in certain localities, diarrheal diseases were fairly common. For example, a temple death register from Hida province that recorded causes of death in the late eighteenth and early nineteenth centuries documents a fairly severe epidemic in the autumn of 1826. Dysentery claimed 59 lives within a 6-week period; the victims were mostly children under 10 years of age. But such epidemics were unusual. It was more common for diarrheal diseases to claim a few lives each year in the later summer or autumn than to erupt in major epidemics.An enteric disease that did attract national attention in the late Tokugawa period was “Asiatic” cholera. The first cholera pandemic, which began to spread outside of India in 1817, reached Japan toward the end of 1822. It followed the pattern typical of imported diseases in Japan by breaking out first in the port of Nagasaki, where it ws heralded as a new disease. It spread from there in a northeasterly direction to Kyoto and Osaka, but died out, presumably because of the cold weather, before reaching the capital at Edo. Ironically, the disease that was known in the West as “Asiatic” cholera was known in Japan as “the disease of the Western barbarians.”
There is no ftu*ther evidence of cholera in Japan until 1858, when it once again arrived in Nagasaki, this time on the American ship Mississippi. The fact that there were no outbreaks of cholera in Japan between 1822 and 1858 is remarkable, because it was during this period that the disease became a major threat to cities of the West. But Japan’s political cordon sαnitαire seems to have been effective in keeping cholera out. By the late 1850s, however, after its ports had beeen opened to international trade by American gunboats, Japan was stricken by the same pandemics that affected other world regions.
It is much more difficult to identify the nonepidemic or chronic diseases of the early modern period, but there is no doubt that venereal diseases were common. Gonorrhea was an old disease in Japan and presumably had a wide distribution. However, a new venereal disease that was probably syphilis reached Japan around 1513. The Japanese called it “the great pox” - the same name that Europeans had given to syphilis a short time before. The Japanese later claimed that syphilis had been brought to them by the Portuguese, but as the Portuguese did not reach Japan until 1543, this conclusion is questionable. Syphilis probably spread from Portuguese to Japanese or Ryukyuan traders in the East Indies in the early sixteenth century, and then subsequently entered Japan on East Asian ships.
By 1600 syphilis was a major health problem in Japan’s large cities. Sixteenth-century European observers had reported that it was widespread among the Japanese population, and contemporary Japanese writers claimed that in Edo more doctors treated syphilis than any other disease. Fully 9.64 percent of the human skulls that have been excavated from several Edo period sites in and around Tokyo show cranial lesions caused by tertiary syphilis (8.8 percent male; 5.9 percent female). This rate seems quite high, especially when one considers that the incidence of earlier stage syphilis in the population would have been much higher than the incidence of tertiary syphilis. However, when one considers the high proportion of males in the population of Edo and the numerous licensed pleasure quarters and widespread prostitution, perhaps a high rate of syphilis morbidity and mortality was to be expected.