“We’re really unclear as to how these microbes are going to interact with the modern environment,” Miner said. Twitter/@CTVNews

Scientists have revived a 'zombie' virus that spent 48,500 years frozen in permafrost.

Warmer temperatures in the Arctic are thawing the permafrost, a frozen layer of soil beneath the surface, and maybe reactivating viruses that have lain dormant for thousands of years and could be dangerous to both human and animal health.

Though the idea of a pandemic caused by a disease from the past sounds like the plot of a science fiction film, experts caution that the risks, while low, are not fully understood.

Thaws may also result in the discharge of Cold War-era chemical and radioactive waste that has the potential to damage wildlife and disturb ecosystems.

"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 NASA Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, California.

A fifth of the Northern Hemisphere is covered in permafrost, which has long supported the Arctic tundra and boreal woodlands of Alaska, Canada, and Russia.

Along with ancient viruses, it acts as a kind of time capsule, preserving the mummified remains of several extinct animals, including two cave lion cubs and a woolly rhino, that scientists have recently been able to find and study.

Not only is permafrost cold, but it also lacks oxygen and is opaque to light, making it an ideal storage medium.

However, the Arctic is currently warming up to four times faster than the rest of the world, which is weakening the region's top layer of permafrost.

Jean-Michel Claverie, an emeritus professor of medicine and genomics at the Aix-Marseille University School of Medicine in Marseille, France, has examined earth samples taken from Siberian permafrost to see whether any viral particles contained therein are still infectious in order to better understand the dangers posed by frozen viruses.

He's looking for what he calls "zombie viruses," and he's discovered some of them.

Claverie researches a specific virus subtype that he first identified in 2003.

Giant viruses are a good model for this kind of lab work because they are larger than the normal variety and can be seen with a standard light microscope rather than a more potent electron microscope.

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 places across Siberia and showed they could each infect cultured amoeba cells.

"We view these amoeba-infecting viruses as surrogates for all 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 are there. We don't know for sure that they are still alive. But our reasoning is that if the amoeba viruses are still alive, there is no reason why the other viruses will not be still alive, and capable of infecting their own hosts."

Permafrost has been found to have remnants of bacteria and viruses that can harm people.

The genome of the influenza strain that caused the 1918 pandemic was found in the lungs of a woman whose body was exhumed from permafrost in a village on the Seward Peninsula of Alaska in 1997.

In 2012, it was determined by experts that the 300-year-old mummified remains of a woman buried in Siberia had the genetic markers for the smallpox virus.

The deeper thawing of the permafrost during exceptionally hot summers has also been linked to an anthrax outbreak in Siberia that affected dozens of people and more than 2,000 reindeer between July and August of 2016.

This allowed old Bacillus anthracis spores to resurface from old burial grounds or animal carcasses.

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

"You must remember our immune defense has been developed in close contact with microbiological surroundings," said Evengård, who is part of the CLINF Nordic Centre of Excellence, a group that investigates the effects of climate change on the prevalence of infectious diseases in humans and animals in northern regions.

"If there is a virus hidden in the permafrost that we have not been in contact with for thousands of years, it might be that our immune defense is not sufficient," she said.

"It is correct to have respect for the situation and be proactive and not just reactive. And the way to fight fear is to have knowledge."

Of course, in the real world, scientists are unsure of how long these viruses might continue to be contagious after being exposed to the current environment or how likely it would be for the virus to come into contact with a suitable host.

Some viruses are benign or even helpful to their hosts; not all viruses are pathogens that can spread disease.

The risk of human exposure to ancient viruses is extremely low in the Arctic, which is still a sparsely populated region despite being home to 3.6 million people.

Still, "the risk is bound to increase in the context of global warming," Claverie said, "in which permafrost thawing will keep accelerating, and more people will populate the Arctic in the wake of industrial ventures."

Claverie is not alone in expressing concern that the area might be ripe for a spillover event, which occurs when a virus infects a new host and begins to spread.

Identifying viruses and other hazards contained in the warming permafrost is the first step in understanding what risk they pose to the Arctic, Miner at NASA's Jet Propulsion Laboratory said.

Other challenges include quantifying where, when, how fast and how deep permafrost will thaw, reports CNN.

"Abrupt thaw rapidly 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 labeled the direct infection of humans with ancient pathogens released from permafrost as "currently improbable."

"We're really unclear as to 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 run."

Miner expressed concern over what she called "Methuselah microorganisms" (named after the Biblical figure with the longest life span).

These organisms have the potential to introduce the dynamics of ancient and extinct ecosystems into the modern Arctic, with unknowable repercussions.

According to Miner, the re-emergence of ancient microorganisms could alter soil composition and vegetative growth, potentially accelerating the effects of climate change.

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