In these troubling times where the global Covid-19 pandemic rages on, Proceedings B has published a timely study that investigated animal-human interactions that have led to a spillover of viruses from animals to humans. The study found that the viruses most likely to spill over to infect humans are those from domestic animals and species better adapted to human landscapes. The spillover risk was also greatest from threatened wild animals that were declining in number due to exploitation or destruction of habitat. Lead author Christine K. Johnson from the Epicenter for Disease Dynamics, University of California, Davis tell us more about the study.
As we are too aware from the news headlines, we are all susceptible to new viruses that emerge from animals. The human population lacks prior exposure and immunity to these viruses, so, for highly transmissible pathogens, the conditions are set for an epidemic to take off. Viruses regularly jump species to infect people, and most are not that dangerous. These viruses are either not that transmissible among humans or they do not cause much disease. But every so often, a pathogen with an unfortunate combination of transmissibility and disease severity leaps over species boundaries to infect the human population. With globalisation, these emerging animal viruses can rapidly be exported to new susceptible communities, resulting in exponential transmission, overwhelming health care systems and causing economic disruption, as we now have in our daily lives.
To head off emergence of viruses like SARS-CoV-2, the coronavirus causing the COVID-19 epidemic, we seek the lessons learned from centuries of spillover from animals to people. This Proceedings B study investigated the number of animal viruses that have been shared with people and analysed the causes of species decline to uncover animal-human interactions that have perpetuated pathogen spillover. These data highlight species that have increased in abundance and adapted to human-modified landscapes, and are likely to continue to be an important source of ongoing pathogen transmission to humans. See Figure 2.
Our findings also provide evidence that human actions, specifically exploitation of wildlife, such as hunting and the wildlife trade, were important drivers of virus spillover. These actions have not only increased risk of virus transmission to people but have furthered the decline of many wildlife species, putting them at risk of extinction. Human encroachment into wildlife habitat has similarly resulted in increased contact with wild animals, heightened rates of virus spillover and created losses in species abundance.
The emergence of the novel coronavirus causing this epidemic is an unfortunate convergence of many ecological and epidemiological drivers of disease spillover. However, these circumstances are not unique to this event. These drivers are occurring all over the world as wildlife shift their distributions to accommodate anthropogenic activities and environmental change. Wild mammals and birds have no shortage of potentially zoonotic viruses to share with us, so when we interact with animals, we are playing a dangerous probability game. This study provides evidence of the public health risk posed by ongoing exploitation of wildlife and impacts to wildlife habitat, with data that can be used to underpin public policy.
When we start to return to normal life after this pandemic, we must find ways to ensure safe and sustainable co-existence with wildlife in our shared environment. We are the dominant species on the planet, and we’ve altered ecosystems for our own benefit for centuries, but ultimately, nature will determine how long we all co-exist.
About the author
I am a Professor of Epidemiology at the One Health Institute at UC Davis. My research is committed to advancing infectious disease investigations at the interface of animal, human, and environmental health through applied research that can inform public policy related to disease prevention and outbreak preparedness. I’m fortunate to work with highly talented coauthors at the Epicenter for Disease Dynamics, where we develop innovative epidemiological analyses to investigate mechanisms underlying disease emergence.
What was your experience like publishing in Proceedings B?
Proceedings B provided exceptionally high-quality, timely, and rigorous reviews that are shared with the paper to enhance transparency in the scientific process. Also, the journal published this article open access because of its relevance to the COVID-19 pandemic. In these challenging times, I’m very appreciative of the journal’s commitment to open science.
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Primates in Nepal – Christine K. Johnson, UC Davis
Christine Krueder Johnson – University of California, Davis