Chapter 3 : Six Plagues of Antiquity

Abstract:

As humans changed their lifestyles, their relationship with infectious diseases came to be altered. For 2 million years these human populations consisted of small groups of hunter-gatherers with limited contact with other such groups, and there were no domesticated animals. Such a population structure, with little or no exposure to new sources of infection and where parasite survival and transmission were minimized, led to a situation in which epidemic diseases were virtually nonexistent. Indeed, only those diseases with very high transmission rates that induced little or no immunity, as well as macroparasitic diseases that did not involve vectors for transmission and sexually transmitted diseases, were able to establish themselves in the groups of hunter-gatherers. Although some vector-borne diseases, such as malaria and yellow fever, may have been present at this stage of human history, it was only after human populations settled down and adopted an agricultural life, or continued a nomadic existence that depended on the husbandry of large herds of animals, that conditions favored the emergence of epidemic diseases (plagues). Historically, plagues (Fig. 3.1) came to be recorded only in our recent past, a time when we became farmers.