Global Environmental Change and Emerging Infectious Diseases: Macrolevel Drivers and Policy Responses

Background: A Primer On Pathogens

We can examine infectious disease emergence on both micro- and macro-levels. On a microscopic (or single pathogen) level, emergence events may have complex mechanisms, prompting various theories about different factors that may lead to disease emergence and spread and their relation to changes in biodiversity or species composition in an ecosystem (Keesing, Holt, & Ostfeld, 2006; Randolph & Dobson, 2012). While microlevel analyses and their interactions with macrolevel processes are useful, the thematic focus of this chapter is on the macrolevel, where emergence is driven by the many anthropogenic impacts that are altering ecological dynamics on a large scale, leading to global environmental change. For example, land conversion for agricultural uses and livestock production and other anthropogenic activities have increased or led to new types of human or domestic animal contact with wildlife, thereby facilitating pathogen “spillover” to humans (Jones et al., 2008; Karesh et al., 2012). At the same time, the rapid expansion in trade and travel in recent decades also establishes new pathways for the spread of dangerous pathogens, including through the introduction of invasive species and the climatic and other habitat conditions that allow them to persist (Mazza, Tricarico, Genovesi, & Gherardi, 2014). To examine the broad drivers leading to disease emergence, a basic comprehension of infectious disease dynamics is needed.