Pandemics: the heat is on

As the earth’s climate continues to warm, researchers predict wild animals will be forced to relocate from their current habitats – likely to regions with large human populations – dramatically increasing the risk of a viral jump to humans that could lead to the next pandemic. 

This link between climate change and viral transmission is described by an international research team led by scientists at Georgetown University and was published on April 28 in Nature.

In the study, scientists conducted the first comprehensive assessment of how climate change will restructure the global mammalian virome. The work focuses on geographic range shift – the journeys that species will undertake as they follow changing habitats into new areas. As they encounter other mammals for the first time, the study projects they will share thousands of viruses.

The researchers say these shifts will bring greater opportunities for viruses like Ebola or coronaviruses to emerge in new areas, making them harder to track, and spread into new types of animals, making it easier for viruses to jump across a “stepping stone” species into humans.

“The closest analogy is actually the risks we see in the wildlife trade,” says the study’s lead author Professor Colin Carlson, an assistant research professor at the Center for Global Health Science and Security at Georgetown University Medical Center. “We worry about markets because bringing unhealthy animals together in unnatural combinations creates opportunities for this stepwise process of emergence – like how SARS jumped from bats to civets, then civets to people. But markets aren’t special anymore; in a changing climate, that kind of process will be the reality in nature just about everywhere.”

Of concern is that animal habitats will move disproportionately to the same places as human settlements, creating new hotspots of spillover risk. Much of this process may already be underway in today’s 1,2-degree warmer world, and efforts to reduce greenhouse gas emissions may not stop these events from unfolding.

An additional important finding is the impact that rising temperatures will have on bats, which account for the majority of novel viral sharing. Their ability to fly will allow them to travel long distances, and share the most viruses. Because of bats’ central role in viral emergence, the greatest impacts are projected in southeast Asia, a global hotspot of bat diversity.

“At every step,” says Carlson, “our simulations have taken us by surprise. We’ve spent years double-checking those results, with different data and different assumptions, but the models always lead us to these conclusions. It’s a really stunning example of just how well we can, actually, predict the future if we try.”

“It’s unclear exactly how these new viruses might affect the species involved, but it’s likely that many of them will translate to new conservation risks and fuel the emergence of novel outbreaks in humans,” says the study’s co-lead author Professor Gregory Albery, a postdoctoral fellow in the Department of Biology in the Georgetown University College of Arts and Sciences.

Altogether, the study suggests that climate change will become the biggest upstream risk factor for disease emergence – exceeding higher-profile issues like deforestation, wildlife trade, and industrial agriculture. The authors say the solution is to pair wildlife disease surveillance with real-time studies of environmental change.

“When a Brazilian free-tailed bat makes it all the way to Appalachia, we should be invested in knowing what viruses are tagging along,” says Carlson. “Trying to spot these host jumps in real-time is the only way we’ll be able to prevent this process from leading to more spillovers and more pandemics.”