Scientists revived a virus "zombie" that spent 48,500 years frozen in permafrost

() — Warmer temperatures in the Arctic have led to the melting of the region’s permafrost — a frozen layer of soil underground — and potentially removed viruses that, after lying dormant for tens of thousands of years, could endanger the health of animals. and humans.

Although the possibility of a pandemic from a centuries-old disease sounds like the plot of a science fiction movie, scientists warn that the risks, while low, are underestimated. Chemical and radioactive waste dating back to the Cold War, with the potential to harm wildlife and disrupt ecosystems, can also be released during snowmelts.

“There are a lot of things going on with the permafrost that are concerning, and this shows why it’s very important that we keep as much of the permafrost frozen as possible,” said Kimberley Miner, a climate scientist in NASA’s Reaction Propulsion Laboratory at the Institute for California Tech in Pasadena.

Permafrost covers a fifth of the northern hemisphere and has supported the arctic tundra and boreal forests of Alaska, Canada and Russia for millennia. It serves as a kind of time capsule that preserves, in addition to ancient viruses, the mummified remains of various extinct animals that scientists have been able to unearth and study in recent years, including two cave lion cubs and a woolly rhino.

The reason permafrost is a good preservation medium is not just because of the cold; but it is also an oxygen-free environment in which light does not penetrate. But the current temperatures of the Arctic warms up to four times faster than the rest of the planetweakening 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, analyzed soil samples taken from the Siberian permafrost to see if there are viral particles that are still infectious. He’s on the lookout for what he describes as “zombie viruses,” and he’s already found a few.

the virus hunter

Claverie is studying 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 with a normal light microscope, rather than a more powerful electron microscope, which makes them a good model for this type of laboratory work.

Their efforts to detect viruses frozen in the permafrost were partially inspired by a team of Russian scientists who in 2012 revived a wild flower from 30,000-year-old seed tissue Found in a squirrel’s burrow. (Since then, scientists have also successfully brought ancient microscopic animals to life).

In 2014, managed to revive a virus that 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 reasons, he chose to study a virus that could only attack single-celled amoebas, not animals or humans.

He repeated the feat in 2015, isolating a different type of virus which also attacked amoebas. and in his latest research, published February 18 in the journal VirusesClaverie and his team isolated several ancient virus strains from multiple permafrost samples taken from seven different locations in Siberia and showed that each could infect cultured amoeba cells.

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

That the viruses that infect amoebas are still infectious after so long is indicative of a potentially bigger problem, Claverie said. He fears that people will view his research as a scientific curiosity and miss the possibility 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 .

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

Precedence of human infection

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

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

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

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

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

“If there is a virus hiding in the permafrost that we have not been in contact with for thousands of years, our immune defense may not be sufficient,” he said. “It is correct to have respect for the situation and to be proactive and not just reactive. And the way to combat fear is to have knowledge.”

Viral contagion possibilities

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 find 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 remains a sparsely populated place, making the risk of human exposure to ancient viruses very low.

Still, “the risk will increase in the context of global warming,” Claverie said, “in which permafrost thaw will continue to accelerate and more people will populate the Arctic from industrial enterprises.”

And Claverie is not the only one warning that the region could become fertile ground for a spillover event, triggered when a virus jumps to a new host and begins to spread.

Last year, a team of scientists published an investigation 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 tags and the genomes of potential hosts (plants and animals) in the area.

Using computer model analysis, they suggested that the risk of viruses spreading to new hosts was greatest in locations close to areas where large amounts of glacial meltwater flowed into the lake, a scenario that becomes more Likely as the weather warms up.

unknown consequences

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

Thawing can be a gradual process of just a few centimeters per decade, but it can also occur more rapidly, as in the case of 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 underappreciated factor in climate change.

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

Those potential hazards included buried waste from heavy metal mining and chemicals like the pesticide DDT, which was banned in the early 2000s. Russia and the United States have also dumped radioactive material in the Arctic since the start of nuclear testing. in the 1950s.

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

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

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

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

“It’s really not clear to us how these microbes are going to interact with the modern environment,” he said. “It’s not an experiment that I think any of us want to do.”

The best course of action, Miner said, is to try to stop the larger-scale melting and climate crisis, and keep these dangers buried in the permafrost forever.