The emergence of infectious diseases of zoonotic origin: ecological complexity and socioeconomic responsibility

Abstract

The COVID-19 pandemic has its origins in a constant but rather rare biological phenomenon: the emergence of infectious diseases of zoonotic origin in human populations. The agent of an infectious animal or zoonotic disease depends for its multiplication and dispersion on a wild host species to which it has adapted over time and which constitutes the reservoir of the corresponding infectious disease. If the biotope of this initial host is sustainably modified, the associated biocenosis migrates with its pathogenic flora to a new habitat, enabling the pathogen to change animal host species. If this migration introduces it into the human environment, the infectious agent may pass to humans or to a commensal wildlife or domestic species that will serve as an intermediate host. This ecological mechanism involves multiple and complex interactions that result in a direct link between biodiversity erosion and increased frequency of these emergences in humans. Together with at-risk human socio-economic practices, it determines the distribution of the territories where these diseases emerge worldwide. Chronic diseases and psychosocial vulnerabilities in humans could potentially worsen the phenomenon. To be able to carry out a targeted action to identify and stop an outbreak of an unknown infectious disease, we need to be able to predict which pathogen is most likely to constitute a threat and in which regions of the world. It is a difficult scientific problem that requires a holistic vision of the "one health" type that decompartmentalizes animal health, human health, and ecosystem health, and a transdisciplinary approach focusing on the microbial ecology of infectious diseases, the biology of evolution, and the social sciences.