Emergence of new infectious diseases

Abstract

Abstract This chapter reviews the evolution and ecology of emerging diseases. Human infectious diseases are caused by more than 1400 pathogen species with considerable diversity in lifestyles. Almost all pathogens of newly emerging diseases come from animal reservoirs. Most are viruses, especially RNA viruses. The emergence of a new infectious disease in the human population involves exposure to the pathogen, successful infection of the hosts, and sufficient transmission between hosts. These different levels of emergence make up the ‘pathogen pyramid’. Both ecological and evolutionary changes can affect a pathogen's position on the pyramid. HIV/AIDS, influenza (H5N1), SARS, Ebola, and monkeypox are emerging diseases. From the available data it is hard to tell if ecological changes alone caused these diseases to emerge or if evolutionary changes were sometimes involved as well. The past provides some guidelines as to which kinds of pathogen are most likely to emerge in the future.