Contagion: Staying Safe While Species Share Spaces

Primary Source: Carlson, C.J., Albery, G.F., Merow, C. et al. Climate change increases cross-species viral transmission risk. Nature 607, 555–562 (2022).

As Climate Change reduces the resources available in ecosystems across the world, many species are forced to share the scarce resources in a much smaller area, such as the various species around this watering hole during the exacerbated dry season in Africa. Credit: “Lion in dry season.jpg” by Buiobuione, licensed under CC BY-SA 4.0.

With the Covid-19 Pandemic still fresh in our minds, the study of the spread of viruses is increasingly relevant. Particularly, many scientists have expressed concern for the effects that global climate change may have on the spread of viruses that originate in wildlife, otherwise known as zoonotic viruses. Zoonotic viruses make up a very small fraction of the world’s viruses but can be especially infectious. Since these outbreaks occur when one species infect another species where said virus isn’t common, the new host species is often ill-prepared to combat the zoonotic virus as compared to other viruses typical for their population. As climate change becomes more extreme, the resources that many species rely upon become scarcer and scarcer, ending up concentrated into smaller areas. As a result, many species that normally do not interact with each other are being forced into the same spaces, giving more opportunities for zoonotic viruses to occur, spreading from their original host to a new species in a process called a spillover event. To address these concerns, researchers Carlson, Albery, Merow, and their collaborators modelled the likelihood of spillover events among 3,139 mammal species under various climate and land-use possibilities, using data from the Global Biodiversity Informatics Facility.

Where We Go From Here

As zoonotic viruses are more likely to occur if the overlapping species are closely related, the researchers limited their modeling to mammal species with large amounts of distribution data available to work with. Designing a model to predict how a population of one species of mammal might react to increasing climate is a hard enough task on its own, but this task is made more difficult considering that exactly how climate change affects the environments these species occupy is heavily dependent on humans. With these human-dependent factors, the researchers decided to model the distribution of these mammal species under four different potential futures. These potential futures each assume a different course of action with regards to people’s treatment of climate change and land-use (keeping the global temperature within two degrees Celsius or not, as well as switching to more ecologically friendly land-use practices or not). Doing this for over three thousand species around the world makes their analysis even more complex. With all these models completed, however, they were able to create and compare these scenarios, estimating the amount of potential spillover events each one could potentially produce. Since many species are averse to environmental changes, two of these scenarios were analyzed for each potential future. In one of these scenarios the speed of a species’ range changes is limited, while the other assumes species will change their distribution as fast as possible, regardless of the species’ tendency to avoid range changes.

With their relation to other mammal species and ability to fly, bats, such as this vampire bat, represent a much larger threat to the spread of zoonotic viruses than other mammal species. Credit: “Common vampire bat, Desmodus rotundus.jpg” by Gerry Carter, licensed under CC BY-SA 4.0.
Better Safe Than Sorry

The various scenarios predicted by these models unfortunately foresee a notable increase in potential spillover events, even among the most environmentally conscious climate change, land-use, and range-distribution speed possibilities. These spillover events are most likely to occur in tropical areas of Africa, and especially so in southeast Asia. While these spillover events represent danger on their own, the geographic distribution of these events is even more concerning. This is because of the large amount of interaction with wildlife in these parts of the world, increasing the chances of zoonotic viruses spreading not just among the increasingly endangered wildlife, but also amongst the people neighboring this wildlife. However, while these scenarios may seem bleak, having the knowledge of such scenarios can inform our ability to fight such potential futures. Additionally, the analysis of so many species provided the helpful information about which species represent the largest contribution to the threat of zoonotic viruses. For example, the researchers found that, due likely to their ability to widely expand their range, species of bats represented a much larger spread of novel species-overlap, and thus potential spillover events. With this consideration in mind, protecting the environments of these particular species from climate change and land development for human-use becomes not just an ideal goal for environmentalists, but a vested interest for global health.

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Cypress Novick

Cypress Novick

I am a recent graduate of Occidental College in Los Angeles, California, where I studied for my Bachelor's in Biology. My main research interests are wetlands ecology, mycology, estuary ecosystem interactions, and plant-based trophic interactions. I have always been passionate about making science more available and understandable, and am always trying to improve my writing so I may help myself and others be better understood.

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