Causal inference in disease ecology: investigating ecological drivers of disease emergence

Abstract

Despite awareness that disease emergence may be related to ecological change, few studies have rigorously analyzed the underlying environmental drivers of the dynamics of disease emergence. This may be due to the fact that ecological change and disease emergence are often mediated through complex and large‐scale processes that are not amenable to traditional reductionist approaches to causal inference. Here, we suggest strategies assembled from diverse disciplines, including ecology, epidemiology, and the social sciences, to analyze complex relationships, promote cooperation, increase efficiency, and minimize bias when investigating the ecological drivers of disease emergence. These techniques, which complement traditional hypothesis testing, include epidemiologic causal criteria, strong inference, causal diagrams, model selection, and triangulation. We also present several examples from recent emerging infectious disease investigations, including Hendra virus, Nipah virus, coral diseases, and avian influenza, where these techniques were successfully applied. Here, we outline some of the barriers to advancing our understanding of causation in disease ecology and offer some solutions for investigating large‐scale ecological drivers, such as global warming, pollution, and land‐use change.

Disease and the dynamics of extinction

“…Other criteria that indicate a pathogen may be responsible for population decline are needed. A possible approach is to apply the Bradford Hill criteria [80], which have also been suggested as being useful in understanding the emergence of infectious wildlife diseases [81]. Bradford Hill developed nine criteria to suggest that environmental factors have a causal relationship to human disease.…”

Urban habituation, ecological connectivity and epidemic dampening: the emergence of Hendra virus from flying foxes (Pteropusspp.)

“…Two of these, the paramyxoviruses Hendra and Nipah virus, have caused sporadic outbreaks in domestic animals and people, with extremely high case-fatality rates, and evidence of human-to-human transmission for Nipah virus [12 -14]. The unprecedented emergence of four novel human pathogens from a single host genus in such a short period of time suggests that recent changes in host ecology may play a role in emergence [6]. However, despite their pandemic potential, and the lack of effective therapies or vaccines, little is known about what factors may have caused these bat-borne viruses to emerge.…”

Rôle des oiseaux sauvages dans la transmission et la dispersion des virus de l’influenza aviaire : apport de l’éco-épidémiologie dans les écosystèmes afro-tropicaux

“…Dans les régions tropicales africaines, en l'absence d'information épidémiologique, il a fallu mettre en place un cadre de recherche combinant les sciences de l'épidémiologie et de l'écologie (Caron et al, 2009). Ces travaux ont donc porté sur l'étude des processus écologiques qui sous-tendent les dynamiques de transmission des pathogènes au sein des populations ou des communautés d'hôtes (Plowright et al, 2008 ;Carver et al, 2009). Cette approche s'est structurée afin de comprendre : -quels sont les mécanismes de perpétuation des VIA FP chez les hôtes de maintenance que constituent les oiseaux sauvages ; -quelle est la capacité de dispersion des VIA par les espèces migratrices ; -quels sont les processus de transmission de ces virus à l'interface entre les oiseaux sauvages et la volaille.…”