Abstract
Zoonotic diseases are infectious diseases of humans caused by pathogens that are shared between humans and other vertebrate animals. Previously, pristine natural areas with high biodiversity were seen as likely sources of new zoonotic pathogens, suggesting that biodiversity could have negative impacts on human health. At the same time, biodiversity has been recognized as potentially benefiting human health by reducing the transmission of some pathogens that have already established themselves in human populations. These apparently opposing effects of biodiversity in human health may now be reconcilable. Recent research demonstrates that some taxa are much more likely to be zoonotic hosts than others are, and that these animals often proliferate in human-dominated landscapes, increasing the likelihood of spillover. In less-disturbed areas, however, these zoonotic reservoir hosts are less abundant and nonreservoirs predominate. Thus, biodiversity loss appears to increase the risk of human exposure to both new and established zoonotic pathogens. This new synthesis of the effects of biodiversity on zoonotic diseases presents an opportunity to articulate the next generation of research questions that can inform management and policy. Future studies should focus on collecting and analyzing data on the diversity, abundance, and capacity to transmit of the taxa that actually share zoonotic pathogens with us. To predict and prevent future epidemics, researchers should also focus on how these metrics change in response to human impacts on the environment, and how human behaviors can mitigate these effects. Restoration of biodiversity is an important frontier in the management of zoonotic disease risk.
Highlights
A Confusing Role for Biodiversity in Pathogen Transmission? Thousands of pathogens circulate in the human population; hundreds of these are bacteria [1], hundreds more are viruses [2]; a smaller but still sizeable number are fungi [3]
Zoonotic diseases are infectious diseases of humans caused by pathogens that are shared between humans and other vertebrate animals
We evaluate whether recent evidence allows the effects of biodiversity, its loss, on pathogen emergence to be reconciled with their effects on subsequent transmission
Summary
In the most common conceptual model linking biodiversity to disease emergence, biodiversity is made up of species that host a diversity of pathogens (SI Appendix), any one of which could have the characteristics enabling it to jump successfully into humans (Fig. 1A) [7] Implicit in this model focusing on total host diversity is the assumption that all taxa are likely to be sources of zoonotic pathogens. Johnson et al [21] and Wells et al [31] conducted their analyses with data that included hosts known to have been infected with a particular virus, and for which there was some evidence that they could share the pathogen with humans (SI Appendix) They did not attempt to identify the species that served as the original transmitter of the pathogen to humans: that is, the source of the primary spillover event that first resulted in a human infection.
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