New and Converging Infections

Abstract A major feature of the Third Epidemiological Transition is a major increase in the number of human infections from newly detected pathogen species that originated with non-human animal hosts. This chapter examines the biosocial factors that have driven the spillover of these zoonotic pathogens into the human species as well as the stepwise evolution of their relative virulence and transmissibility. Although issues such as wild-animal hunting and so-called wet markets may have contributed to these processes, large-scale commercial agriculture and resource extraction enterprises play a much larger role by encroaching on wild environments and increasing the size and density of domestic animal populations that can serve as vector species. With respect to potential human host populations, the global trends of urbanization, aging, and poverty have created opportunities for the incubation of new pathogens. All these processes are occurring within extensive networks of trade, migration, and travel.