Southeast Asia can be visualized as the part of Asia that spills into the sea, comprised of long coasts, tidal plains, peninsulas, and islands. There are high mountains, inland plains, plateaus, and upland valleys; nonetheless, to a very large degree, human culture has developed with an acute awareness of water, from the sea, the rivers, and the monsoon rains. It is therefore not surprising that many of the endemic health problems in the region are related to water; indeed, since prehistoric times, nearly all major areas of habitation have been exposed to global contact by water transport.

Maritime routes linking the littoral civilizations of the Eurasian landmass have passed through Southeast Asia for more than two millennia. We can accordingly assume that from early times the region experienced all of the epidemic diseases familiar to the ancient world. What inhibits discussion of diseases in the earlier historical periods of Southeast Asia is the lack of data. Because of the prevailing tropical-equatorial climate, the preservation of written records has, until recently, required greater effort than most human societies were prepared to make. Our first information comes from the observations of Chinese annalists, whose works survived in the temperate climate of northern China. As the Chinese moved southward into what is today northern Vietnam, they recorded perceptions of disease associated with what for them were southern lands.

Most prominent among the health problems encountered by ancient Chinese armies in Vietnam were malaria and other “fevers” associated with the monsoon rain season. Chinese generals timed their expeditions into Vietnam to coincide with the dry season, from November to May.