The Ecology of Pathogen Spillover and Disease Emergence at the Human-Wildlife-Environment Interface

Alexander, Kathleen A.; Carlson, Colin J.; Lewis, Bryan L.; Getz, Wayne M.; Marathe, Madhav V.; Eubank, Stephen G.; Sanderson, Claire E.; Blackburn, Jason K.

Novel diseases are increasingly emerging into human populations through the complex—and often, unseen—stepwise process of spillover from a combination of wildlife, livestock, vectors, and the abiotic environment. Characterizing and modeling the spillover interface are a key part of how eco-epidemiologists respond to the growing global burden of emerging infectious diseases; but the diversity of pathogen life cycles and transmission modes poses a complex challenge for ecologists and clinicians alike. We review our current understanding of the spillover process and present a framework that relates spillover rates and human-to-human transmissibility to the basic reproduction number (R (0)). Using pathogens that exemplify important transmission pathways (anthrax, Ebola, influenza, and Zika), we illustrate key aspects of the spillover interface and discuss implications to public health and management of emerging infectious disease.