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Global shifts in mammalian population trends reveal key predictors of virus spillover risk

Johnson CK, Hitchens PL, Pandit PS, Rushmore J, Evans TS, Young CC, Doyle MM. Proceedings of the Royal Society B: Biological Sciences. 2020 Apr 8; 287(1924): 20192736. https://doi.org/10.1098/rspb.2019.2736

The same processes that threaten wildlife populations increase virus spillover risk

This research identified a higher incidence of zoonotic viruses in mammalian species that have declined in abundance due to habitat loss, fragmentation, and exploitation, providing direct evidence for the impact of environmental change on emerging infectious disease. Improving our understanding of the relationship between human activity and disease emergence gives us insight into how to reduce the risk of viral spillover and prevent the next pandemic. Results from studies like this can inform future public policy and shift thinking from preparedness to prevention.

Jump to:  Key Findings   |   Figures   |   Conservation and Human Health   |   Impact and Influence   |   Next Steps

Key Findings

  • Exploitation of wildlife and loss of natural habitat are key drivers in the emergence of zoonotic diseases that spread from wildlife to humans.

  • ❯  As human populations continue to expand, requiring more land (habitat destruction) and greater food resources (agriculture, wildlife hunting, wildlife trade), human-animal interactions will continue to increase, and the corresponding emergence of zoonotic viruses will also increase — exposing humans to a greater number of pathogens with pandemic potential, such as the current COVID-19 pandemic.

    ❯  Large-scale human encroachment into wildlife habitat has resulted in wildlife movement and increased human contact with wild animals, heightening rates of virus spillover, creating losses in species abundance, and, for many species, threatening them with extinction. Movement and redistribution of wildlife often enhance disease spread in wildlife populations, resulting in epidemics in wildlife and increased risk of spillover to humans when these epidemics are at their peak, especially if wildlife have relocated close to human communities.

    ❯  Loss of biodiversity from over-exploitation and deforestation increases viral spillover risk, not only as humans interact more directly with wildlife, but also because losing species diversity can favor a higher abundance of some species that are especially well adapted to zoonotic viruses.
  • Domesticated animals had a higher number of zoonotic viruses per species, which is a consequence of their global abundance and the very close interactions people have had with domesticated species over centuries.
  • ❯  Humans have a long history of close interaction with domesticated species, resulting in shared viruses.

    ❯  Domestic animals can also amplify infections as an intermediary for transmission of viruses from wildlife to humans.

  • Wildlife species which have adapted well to human-modified habitats frequently carry zoonotic viruses and have increased potential for interactions with humans that facilitate disease transfer.
  • ❯  Wild animal species that have been best able to adapt to human-altered landscapes (e.g., rats and mice, rhesus macaques living in urban environments) are more likely to have close contact with humans, increasing the likelihood of viral spillover.


RSPB figure 2

Zoonotic Viruses in Threatened Taxa

Number of mammalian viruses shared with humans for each taxonomic order by IUCN threatened species criteria. 

network diagram

Network of Mammalian Species and their Zoonotic Viruses

Bipartite network showing wild and domesticated mammalian species and their zoonotic virus associations. Host species harboring the same zoonotic virus are linked by the viruses they share.

Conservation and Human Health

Humans have drastically changed the planet and nearly one-third of all vertebrate species are threatened or endangered according to the IUCN Red List. As natural habitats are diminished, wildlife adapt in movement and behavior and risk coming into closer contact with people. As a result of this, infectious diseases emerging from wildlife are increasing, at the same time that emerging pathogens have more potential to spread widely through travel and trade.

We must acknowledge these risks and work towards more sustainable ways for humans and wildlife to coexist and minimize disease emergence. Results from studies like this can inform and drive decisions around ecosystem management, sustainable development and environmental policy to help prevent the next pandemic.

Impact and Influence

This research paper was ranked among Altmetric's top 50 research papers published in 2020 in terms of impact and influence. Our findings have been used to underpin policy and legislative initiatives related to environmental change and disease risk by the United Nations, the European Union, and national and state governments. Data and figures from this paper have been included in several UN policy pieces, invited testimony and congressional briefings, the National Geographic journal, and a live musical performance. These efforts highlight environmental change at the root of emerging disease threats and loss of biodiversity, making the case for a One Health strategy needed to advance human, animal, and environmental health in the 21st century.​​​​​

Related Policy Documents             Press Coverage


Next Steps

Given the close linkage between habitat loss and viral spillover, an important next step is to study the specific types of habitat loss and the ecology of disease in relevant wildlife species, to determine which factors are most associated with ecosystem change and increased risk of spillover.

Some of our current projects are exploring the relationships between landscape change, virus transmission, and spillover. Learn more about them here:

EpiCenter for Emerging Infectious Disease Intelligence             Pathogen Plasticity Project