Scientists have revived a ‘zombie’ virus that spent 48,500 years in permafrost

(CNN) Warmer temperatures in the Arctic are thawing the region’s permafrost – a frozen layer of soil underground – and potentially disruptive viruses that, after lying dormant for tens of thousands of years, can 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 risk, although low, is underestimated. Chemical and radioactive waste dating back to the Cold War, which has the potential to harm wildlife and disrupt ecosystems, may also be released during thawing.

“There’s a lot going on with the permafrost that’s cause for 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 NASA’s Jet Propulsion Laboratory at California Institute of Technology in Pasadena, California.

Permafrost covers one fifth of the Northern Hemisphere, underlying the arctic tundra and boreal forests of Alaska, Canada and Russia for millennia. It functions as a kind of time capsule that preserves – in addition to ancient viruses – the mummified remains of a number of extinct animals that scientists have been able to uncover 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 through which light does not penetrate. But Arctic temperatures today 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, emeritus professor of medicine and genomics at Aix-Marseille University School of Medicine in Marseille, France, tested soil samples taken from Siberian permafrost to see if virus particles. contained therein are still infectious. 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 sub-sample room at the Alfred Wegener Institute in Postsdam, where the cores of permafrost were stored.

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 are visible under a regular light microscope rather than a more powerful electron microscope – making them a good model for this type laboratory work.

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

In 2014, he succeeded in reviving 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. To be safe, he had chosen to study a virus that could only target single-celled amoebae, not animals or humans.

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

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

The latest strains represent five new families of viruses, in addition to the two he had revived previously. The oldest was nearly 48,500 years old, based on 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 specimens, found in the stomach contents and fur of a woolly mammoth’s remains, were 27,000 years old.

That amoeba-infecting viruses are still infectious after such a long time indicates a potentially larger problem, Claverie said. He fears that people view his research as a scientific curiosity and do not perceive the prospect of ancient viruses coming back to life as a serious threat to public health.

“We see these amoeba-infecting viruses as surrogates for all the other possible viruses that might be in the 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 virus is still alive, there’s no reason the other viruses won’t still be alive and able to infect their own hosts.”

Precedent of human infection

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

A lung sample from a woman’s body excavated in 1997 from permafrost in a village on Alaska’s Seward Peninsula contained genomic material from the strain of influenza responsible for the 1918 pandemic. In 2012, researchers confirmed that the 300-year-old mummified remains 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 people and more than 2,000 reindeer between July and August in 2016 has also been linked to the deeper thawing of permafrost during unusually warm summers, allowing ancient spores of Bacillus anthracis to reemerge from old burial sites or animal carcasses.

Birgitta Evengård, professor emerita at Umeå University’s Department of Clinical Microbiology in Sweden, said there should be better monitoring of the risk of potential pathogens from thawing permafrost, but cautioned against an alarmist approach.

“You have to remember that our immune system is developed in close contact with the microbiological environment,” says Evengård, who is part of the CLINF Nordic Center of Excellence, a group that investigates the effects of climate change on the occurrence of infectious diseases in humans and animals in the northern regions.

“If there’s a virus hidden in the permafrost that we haven’t been in contact with for thousands of years, it could be that our immune system is not sufficient,” she said. “It is correct 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 area for the team that took cores that Claverie used in his experiments.

Chances of viral transmission

Of course, in the real world, scientists don’t know how long these viruses can remain infectious once exposed to current conditions, or how likely the virus is to encounter a suitable host. Not all viruses are pathogens that can cause disease; some are benign or even beneficial to their hosts. And although it is 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 bound to increase with global warming,” Claverie said, “where thawing of permafrost will continue to accelerate and more people will populate the Arctic in the wake of industrial ventures.”

And Claverie is not alone in warning that the region could become fertile ground for a contagion 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 taken from Lake Hazen, a freshwater lake in Canada located within the Arctic Circle. They sequenced the genetic material in the sediment to identify viral signatures and the genomes of potential hosts – plants and animals – in the area.

Using a computer model analysis, they suggested that the risk of viruses spreading to new hosts was higher in places close to large amounts of glacial meltwater flowing into the lake – a scenario that will become more likely as the climate warms.

Cores of permafrost samples are depicted in a container.

Unknown consequences

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

Thawing can be a gradual process of as little as centimeters per second. decade, but also happens faster, as for example in the case of massive land slopes that can suddenly reveal deep and ancient layers of permafrost. The process also releases methane and carbon dioxide into the atmosphere—an overlooked and underappreciated driver of climate change.

Permafrost thaw can be gradual or happen much faster.

Miner cataloged a number of potential hazards currently frozen in Arctic permafrost in a 2021 article published in the scientific journal Nature Climate Change.

These possible hazards 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 US – since the advent of nuclear testing in the 1950s.

“Abrupt thaw rapidly exposes old permafrost horizons and releases compounds and microorganisms sequestered in deeper layers,” Miner and other researchers noted in the 2021 paper.

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

However, Miner said she is 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 into the present Arctic with unknown consequences.

The resurgence of ancient microorganisms has the potential to alter soil composition and vegetative growth, possibly further accelerating the effects of climate change, Miner said.

“We’re really unclear about how these microbes will interact with the modern environment,” she said. “It’s not really an experiment that I think any of us want to run.”

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

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