Disease Emergence and Re-emergence Prior to 1850

Infectious diseases have been evolving since the dawn of humankind. In Section 1.3, we noted some of the palaeopathological studies that have extended our knowledge of the occurrence of human infections back into pre-history, while recent genetic studies have indicated that the agents of diseases such as malaria (Plasmodium spp.) and leprosy (Mycobacterium leprae) first emerged in the human species many thousands of years ago (Carter and Mendis 2002; Monot et al. 2005). For the most part, however, our knowledge of the long history of disease emergence is based on the written record of earlier ages. In the present chapter, in so far as the historical evidence allows, we provide a brief and necessarily highly selective overview of disease emergence and cyclical re-emergence from the beginning of the written record to the mid-nineteenth century. McMichael (2004) identifies four great historical transitions in the relationship of humans and microbes that, since the initial advent of agriculture and livestock herding, have promoted the emergence and re-emergence diseases. These four transitions, each associated with a progressive increase in the geographical scale of operation (local → continental → intercontinental → global), are: (i) First historic transition (5,000–10,000 years ago). A local transition when early agrarian-based settlements brought humans into contact with sylvatic enzootic pathogens. As described under the ‘domestic-origins hypothesis’ in Section 1.3.2, close and prolonged exposure to domesticated animals and urban pests (for example, rodents and flies) resulted in the cross-species transmission of the ancestral agents of many modern-day human infectious diseases, including influenza, measles, smallpox, tuberculosis, and typhoid. (ii) Second historic transition (1,500–3,000 years ago). A continental-level transition fuelled by the military and trade contacts of early Eurasian civilizations which resulted in the cross-civilization transmission of infectious agents. In the wake of this historical transition, a trans- European ‘equilibration’ of infectious agents occurred and the diseases became endemic to the population. (iii) Third historic transition (200–500 years ago). An intercontinental transition associated with European expansion, resulting in the transoceanic spread of infectious agents.