As climate change accelerates the melting of ice in the Arctic, carbon dioxide emissions, habitat loss and rising sea levels aren’t the only threats humans face. Scientists have shown that ancient “zombie viruses” frozen for thousands of years can reawaken with rising temperatures.
In a paper posted on the preprint server bioRxiv in November, scientists detail how they revived several of these viruses from the Siberian permafrost. The oldest is a 48,500-year-old pandoravirus, which set a world record for the age of a restored virus, co-author Jean-Michel Claverie, a genomicist at Aix-Marseille University in France, tells New Scientist’s Michael Le Page.
All viruses the team uncovered infect only amoebas and therefore are not direct threats to public health. But they were still alive and able to replicate—an indication that dormant viruses dangerous to humans could also be revived from lurking in the ice.
“If the authors are indeed isolating live viruses from ancient permafrost, it is likely that the even smaller, simpler mammalian viruses would also survive frozen for eons,” Eric Delwart, a molecular virologist from the University of California, San Francisco, who was not involved in the research, tells New Scientist.
In fact, a deadly outbreak attributed to melting permafrost has already happened. In 2016, a heatwave in Russia thawed a 75-year-old frozen reindeer carcass infected with anthrax. As the disease spread, dozens of people were hospitalized, one child was killed and thousands of reindeer fell ill. Researchers are warning this may become more common.
“The public health risk is coming from the accelerated release of previously frozen viruses combined with increased human exposure, since global warming is also making Arctic areas much more accessible to industrial development,” Claverie tells Newsweek’s Pandora Dewan. However, Delwart tells New Scientist it's more likely that a zombie virus would circulate in wild or domestic animal populations than create a pandemic-scale outbreak in humans.
Claverie and his colleagues have previously uncovered zombie viruses. Back in 2014, they revived a 30,000-year-old pandoravirus. In their new paper, they describe 13 new viruses isolated from nine samples, including seven samples from permafrost.
Permafrost covers about 24 percent of landmass surfaces in the Northern Hemisphere, and it makes up almost half of the organic carbon stored in Earth’s soil, per the Arctic Institute. Just 3 degrees Celsius of warming could melt 30 to 85 percent of the top permafrost layers in the Arctic. Exactly which microbes this melting could resurface is unknown. Just a single gram of Arctic permafrost can contain hundreds to thousands of microbe groups.
“We really don’t know what’s buried up there,” Birgitta Evengård, a microbiologist at Umeå University in Sweden, told NPR’s Michaeleen Doucleff after the anthrax outbreak in 2016. “This is Pandora's box.”
Rebecca Katz, a global health expert at Georgetown University who was not involved in the research, tells New Scientist the dangers should be taken seriously.
“It makes sense to understand all of the potential pathways for emergence so we can be as prepared as possible,” she tells the publication. “Ancient viruses being released by the thawing permafrost is a very real threat.”