Viruses in permafrost: Scientists have resurrected a ‘zombie’ virus that spent 48,500 years frozen

(CNN) Warmer temperatures in the Arctic are melting the region’s permafrost – a frozen layer of ground beneath the ground – and potentially stirring viruses that, after lying dormant for tens of thousands of years, could endanger animal and human health.

While a pandemic triggered by a disease from the distant past sounds like the plot of a sci-fi movie, scientists warn that the risks, while small, are underestimated. Chemical and radioactive waste dating from the Cold War, which can harm wildlife and disrupt ecosystems, can also be released during the thaw.

“There are a lot of things going on with permafrost that are concerning, and (this) really shows why it’s super important that we keep as much permafrost frozen as possible,” said Kimberley Miner, a climatologist at NASA’s Jet Propulsion Laboratory. at the California Institute of Technology in Pasadena, California.

Permafrost covers one-fifth of the northern hemisphere, having supported the arctic tundra and boreal forests of Alaska, Canada and Russia for millennia. It serves as a sort of time capsule, preserving – in addition to ancient viruses – the mummified remains of a number of extinct species. animals that scientists have been able to unearth and study in recent years, including two cave lion cubs and a woolly rhinoceros.

The reason permafrost is a good storage medium isn’t just because it’s cold; it is an oxygen-free environment that light does not penetrate. But current Arctic temperatures are warming up to four times faster than the rest of the planet, weakening the top layer of permafrost in the region.

To better understand the risks posed by frozen viruses, Jean-Michel Claverie, professor emeritus of medicine and genomics at the Faculty of Medicine of the University of Aix-Marseille in Marseille, France, tested soil samples taken on Siberian permafrost to see if virus particles contained therein are still contagious. He’s on the hunt for what he describes as “zombie viruses” – and he’s found some.

Jean-Michel Claverie is pictured here working in the subsampling room at the Alfred Wegener Institute in Postsdam, where permafrost cores were kept.

The virus hunter

Claverie studies a particular type of virus that he first discovered in 2003. Known as giant viruses, they are much larger than the typical variety and visible under a regular light microscope, rather than an electron microscope more powerful – making it a good model for this. type of laboratory work.

His efforts to detect viruses frozen in permafrost were partly inspired by a team of Russian scientists who, in 2012, revived a wildflower from 30,000-year-old seed tissue found in a tree burrow. ‘squirrel. (Since then, scientists have also managed to bring ancient microscopic animals back to life.)

In 2014, he managed to revive a virus he and his team isolated from permafrost, making it infectious for the first time in 30,000 years by inserting it into cultured cells. For safety reasons, he chose to study a virus that could only target single-celled amoebae, not animals or humans.

He repeated the feat in 2015, isolating a different type of virus that also targeted amoebas. And in his latest research, published Feb. 18 in the journal Viruses, Claverie and his team isolated several ancient virus strains from several permafrost samples taken from seven different locations across Siberia and showed that they could each infect cultured amoeba cells.

This is a computer enhanced photomicrograph of Pithovirus sibericum which was isolated from a 30,000 year old permafrost sample in 2014.

These latest strains represent five new virus families, in addition to the two he had previously resurrected. The oldest was nearly 48,500 years old, according to radiocarbon dating of the soil, and came from a soil sample taken from an underground lake 16 meters (52 feet) below the surface. The youngest samples, found in the stomach contents and fur of the remains of a woolly mammoth, were 27,000 years old.

The fact that viruses infecting amoebas are still infectious after so long points to a potentially bigger problem, Claverie said. He fears that people will see his research as a scientific curiosity and fail to see the prospect of ancient viruses coming back to life as a serious threat to public health.

“We consider these amoeba-infecting viruses to be surrogates for all other possible viruses that could be found in permafrost,” Claverie told CNN.

“We see the traces of many, many, many other viruses,” he added. “So we know they’re there. We don’t know for sure they’re still alive. But our reasoning is that if the amoeba viruses are still alive, there’s no reason for other viruses are not yet alive and capable of infecting their own hosts.”

History of human infection

Traces of viruses and bacteria that can infect humans have been found preserved in the permafrost.

A lung sample from a woman’s body exhumed in 1997 from permafrost in a village on Alaska’s Seward Peninsula contained genomic material from the influenza strain responsible for the 1918 pandemic. In 2012, scientists confirmed that the remains 300-year-old mummified bodies of a woman buried in Siberia contained the genetic signatures of the virus that causes smallpox.

An anthrax outbreak in Siberia that affected dozens of humans and more than 2,000 reindeer between July and August 2016 has also been linked to deeper permafrost thawing during unusually hot summers, allowing ancient Bacillus spores anthracis to resurface from old cemeteries or animal carcasses.

Birgitta Evengård, professor emeritus in the Department of Clinical Microbiology at Umea University in Sweden, said there should be better monitoring of the risk posed by potential pathogens as permafrost thaws, but cautioned against guard against an alarmist approach.

“You have to remember that our immune defense was developed in close contact with a microbiological environment,” said Evengård, who is part of the Nordic Center of Excellence CLINF, a group that studies the effects of climate change on disease prevalence. infections in humans and animals in the northern regions.

“If there’s a virus lurking in the permafrost that we haven’t come into contact with for thousands of years, maybe our immune defense isn’t strong enough,” he said. she stated. “It’s okay to have respect for the situation and to be proactive and not just reactive. And the way to fight fear is to have knowledge.”

A boat served as a canteen and storage space for the team that collected the cores Claverie used in his experiments.

Risks of viral spread

Of course, in the real world, scientists don’t know how long these viruses might remain infectious once exposed to current conditions, or how likely the virus is to encounter a suitable host. Not all viruses are disease-causing pathogens. some are benign or even beneficial to their hosts. And despite being home to 3.6 million people, the Arctic is still a sparsely populated place, making the risk of human exposure to ancient viruses very low.

Still, “the risk is set to increase in the context of global warming,” Claverie said, “in which permafrost melt will continue to accelerate and more people will populate the Arctic as a result of undertakings industrial”.

And Claverie is not alone in warning that the region could become fertile ground for a spillover event – when a virus jumps into a new host and begins to spread.

Last year, a team of scientists published research on soil and lake sediment samples collected from Lake Hazen, a freshwater lake in Canada located within the Arctic Circle. They sequenced genetic material in the sediments to identify viral signatures and the genomes of potential hosts – plants and animals – in the region.

Using computer model analysis, they suggested that the risk of virus spreading to new hosts was higher at locations close to where large amounts of glacial meltwater had poured in. in the lake – a scenario that becomes more likely as the climate warms.

Permafrost sample cores are shown in a container.

Unknown consequences

Identifying viruses and other hazards contained in warming permafrost is the first step to understanding the risk they pose to the Arctic, said Miner of NASA’s Jet Propulsion Laboratory. Other challenges include quantifying where, when, how quickly and how deep the permafrost will thaw.

Thawing can be a gradual process of just a few centimeters per decade, but it also happens more quickly, as with massive landslides that can suddenly expose deep, old layers of permafrost. The process also releases methane and carbon dioxide into the atmosphere – an overlooked and underestimated driver of climate change.

Thawing of permafrost can be gradual or occur much more quickly.

Miner listed a range of potential hazards currently frozen in Arctic permafrost in a 2021 paper published in the scientific journal Nature Climate Change.

These possible dangers included buried waste from heavy metal mining and chemicals such as the pesticide DDT, which was banned in the early 2000s. Radioactive material has also been dumped in the Arctic – by Russia and the United States – since the advent of nuclear testing in the 1950s.

“A sudden thaw quickly exposes old permafrost horizons, releasing compounds and microorganisms sequestered in deeper layers,” Miner and other researchers noted in the 2021 paper.

In the research paper, Miner called direct infection of humans by ancient pathogens released from permafrost “currently unlikely.”

However, Miner said she was concerned about what she called “Methuselah microorganisms” (named after the biblical figure with the longest lifespan). These are organisms that could bring the dynamics of ancient and extinct ecosystems to the current Arctic, with unknown consequences.

The re-emergence of ancient microorganisms has the potential to alter soil composition and vegetative growth, perhaps further accelerating the effects of climate change, Miner said.

“We really don’t know how these microbes are going to interact with the modern environment,” she said. “It’s not really an experiment that I think any of us want to conduct.”

The best course of action, Miner said, is to try to stop the thaw and the broader climate crisis, and to keep those dangers buried in the permafrost for good.

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