Climate change will accelerate viral spillovers, finds study

Over the next 50 years, climate change will drive thousands of viruses to jump from one species of mammal to another, according to a study published in Nature on Thursday. The shuffling of viruses among animals may increase the risk that one will jump into humans and cause a new pandemic, the researchers said.

Scientists have long warned that a warming planet may increase the burden of diseases. But climate change might also usher in entirely new diseases, by allowing pathogens to move into new host species.

“We know that species are moving, and when they do, they’re going to have these chances to share viruses,” said Colin Carlson, a biologist at Georgetown University and a co-author of the new study. Dr Carlson and colleagues built a computer model of potential spillovers in a warming world, projecting how thousands of mammals might shift their ranges as the climate changes between now and 2070.

As temperatures increase, many species are expected to spread away from the blazing Equator to find more comfortable habitats. Others may move up the sides of hills and mountains to find cooler altitudes. When different species come into contact for the first time, the viruses may be able to infect new hosts.

To understand the odds of a successful new infection, the researchers began by building a database of viruses and their mammalian hosts. Some viruses have been found in more than one species of mammal, which means that they must have jumped the species barrier at some point in the past. Using machine learning, they developed a model that could predict whether two host species share a virus.

The more two species overlap geographically, the more likely they were to share a virus because the hosts were more likely to encounter each other, giving viruses more opportunities to move.

Carlson and colleagues also showed that closely related species were more likely to share a virus, which may also be able to evade an immune system similar to one to which it’s already adapted. These findings enabled the researchers to make predictions about what would happen when mammal species come together for the first time in a hotter world.

Among the 3,139 species studied, the researchers anticipated more than 4,000 instances in which viruses would move from one species to another, indicating the sheer scale of what’s to come.

“When you’re trying to predict the weather, you don’t predict individual raindrops,” said Christopher Trisos, an ecologist at the University of Cape Town and a co-author of the study. “You predict the clouds themselves.”

Rachel Baker, a disease ecologist at Princeton University who was not involved in the study, said that the research was an important step forward in understanding how climate change will affect the world’s dangerous viruses. “It’s a great advance,” she said. “We want to know as soon as possible if there’s some link between climate change and pathogen spillover.”

Bats in Southeast Asia will be especially prone to these transmissions, the researchers found. As of now, many bat species in that region are limited to small ranges and don’t come into contact with each other much. But as the planet warms, these bats will fly quickly to suitable climates and encounter new species.

These findings may be particularly ominous for humans. As viruses move to new host species, they evolve — and potentially making them more likely to infect people. In their computer model, the researchers found that there has already been sufficient climate change to start mixing viruses up. “The amount of warming we’ve had has been enough to set it in motion,” Carlson said.