Scientists have made a remarkable discovery in the Siberian permafrost – the revival of a virus that was frozen for 48,500 years. The discovery has raised concerns about the risks of ancient viruses being unleashed as a result of the warming temperatures in the Arctic that are causing the permafrost to thaw.
The permafrost, which covers a fifth of the Northern Hemisphere, is a frozen layer of soil beneath the ground that serves as a time capsule, preserving ancient viruses and the remains of extinct animals. However, current-day Arctic temperatures are warming up to four times faster than the rest of the planet, weakening the top layer of permafrost in the region. This is causing concerns among scientists, who fear that the thawing permafrost could release long-dormant viruses that pose a risk to human and animal health.
To better understand the risks posed by frozen viruses, Jean-Michel Claverie, an Emeritus professor of medicine and genomics at the Aix-Marseille University School of Medicine in Marseille, France, has tested earth samples taken from Siberian permafrost to see whether any viral particles contained therein are still infectious. He is in search of what he describes as “zombie viruses” – viruses that have been frozen for tens of thousands of years but are still capable of infecting living organisms.
Claverie studies a particular type of virus he first discovered in 2003. Known as giant viruses, they are much bigger than the typical variety and visible under a regular light microscope, rather than a more powerful electron microscope – which makes them a good model for this type of lab work.
In 2014, Claverie managed to revive a virus he and his team isolated from the permafrost, making it infectious for the first time in 30,000 years by inserting it into cultured cells. For safety, he had chosen to study a virus that could only target single-celled amoebas, not animals or humans. He repeated the feat in 2015, isolating a different virus type that also targeted amoebas.
In his latest research, published in the journal Viruses, Claverie and his team isolated several strains of ancient virus from multiple samples of permafrost taken from seven different places across Siberia and showed they could each infect cultured amoeba cells. The latest strains represent five new families of viruses, on top of the two he had revived previously. The oldest was almost 48,500 years old, based on radiocarbon dating of the soil, and came from a sample of earth taken from an underground lake 16 meters (52 feet) below the surface. The youngest samples, found in the stomach contents and coat of a woolly mammoth’s remains, were 27,000 years old.
That amoeba-infecting viruses are still infectious after so long is indicative of a potentially bigger problem, Claverie said. He fears people regard his research as a scientific curiosity and don’t perceive the prospect of ancient viruses coming back to life as a serious public health threat. He views these amoeba-infecting viruses as surrogates for all other possible viruses that might be in the permafrost.
“There’s a lot going on with the permafrost that is of concern, and (it) really shows why it’s super important that we keep as much of the permafrost frozen as possible,” said Kimberley Miner, a climate scientist at the NASA Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, California. Chemical and radioactive waste that dates back to the Cold War, which has the potential to harm wildlife and disrupt ecosystems, may also be released during thaws.