A macro ecological approach to zoonotic emerging pathogens: A key role of interspecies barriers, examined by metacommunity and phylogenetic theories
Over 60% of emerging diseases infecting humans are zoonotic and are a major threat to public health globally. Rather than respond to the disastrous effects after their emergence, global strategies should attempt institutional and transdisciplinary collaborations to understand ecological, evolutionary and anthropogenic drivers of disease emergence to develop preventive measures. It is evident that the world’s pandemic prevention strategy is only beginning to take this broader view, as it has traditionally focused on the epidemiological characteristics of individual pathogen strains and on the politics of surveillance, reporting, and trade regulation. Key factors that drive the emergence of zoonotic diseases are related to interactions between human changes to the environment, healthcare, demography, and a background of a large pool of novel pathogens. Macroecology studies large spatial and temporal scales of species distributions where localized ecological patterns transition into global processes. Macroecology complements the study of zoonotic disease ecology by identifying co-evolutionary and biogeographical relationships between parasites and hosts, and suggesting patterns not observed at local scales.
Three major factors that need to be understood to apply any macroecological model in disease ecology include interspecies barriers, metacommunity and phylogenetic theory. Interspecies barriers determine the level of human exposure to a zoonotic pathogen. Then, the human-to-human barrier determines the ability of a pathogen to be transmitted and succeed by infecting another human host and effectively overcome the immune response. In turn, effective transmission of the pathogen may lead to an outbreak, epidemic and eventually a pandemic. So the capacity of a pathogen to cross barriers is essential to understand disease dynamics. In this regard metacommunity and phylogenetic theory include the possibility of a pathogen to persist and spread across different communities throughout the landscapes based on three mechanisms all linked to anthropogenic changes. Some mechanisms proposed by these theories are 1) dispersal, and local extinction of pathogens, reservoir and /or vector hosts, and non-reservoir hosts, thus determining distribution of all species across communities (metacommunity structure); 2) environmental filtering favoring persistence of host and pathogens; and 3) phylogenetic diversity relative to reservoir and/or vector, within and between communities. With this inclusive approach the public health community may better evaluate factors that predispose both time and place to the origin and emergence of infectious diseases.