A conceptual framework for analyzing social-ecological models of emerging infectious diseases

Unraveling mechanisms that underlie new and reemerging infectious diseases (EID) requires exploring complex interactions within and among coupled natural and human (CNH) systems. This scientifi c problem poses one of the most diffi cult challenges for society today (Wilcox and Colwell 2005 ). EID are diseases that have recently increased in incidence or in geographic or host range (e.g., tuberculosis, cholera, malaria, dengue fever), and diseases caused by new pathogens and new variants assigned to known pathogens (e.g., HIV, SARS, Nipah virus, and avian infl uenza) (Morse 2005 ). Wilcox and Gubler ( 2005 ) and Wilcox and Colwell ( 2005 ) argue that transformations in ecological systems caused by multifaceted interactions with anthropogenic environmental changes such as urbanization, agricultural transformations, and natural habitat alterations produce feedbacks that affect natural communities and ultimately their pathogens, animal host, and human populations. These altered "host-pathogen" relationships facilitate pathogen spillover into "new" hosts, rapid adaptations by pathogens, more frequent generation of novel pathogen variants that result in new and reemerging infectious diseases, as well as range expansion and increasing epidemic intensity and frequency of existing diseases.