Viruses frozen for millennia still pose a great danger
Scientists have revived a “zombie” virus that spent 48,500 years frozen in permafrost. Rising temperatures in the Arctic lead to the melting of permafrost in the — frozen layer of soil underground — and potentially cause the emergence of viruses that, having lain dormant for tens of thousands of years, can threaten the health of animals and humans.
While a pandemic caused by a disease from the distant past sounds like the plot of a scientific science fiction film, scientists warn that the risks, while small, are underestimated. Chemical and radioactive waste from the Cold War, which could potentially harm wildlife and disrupt ecosystems, can also be released during thaws, CNN says.
«There's a lot going on with permafrost that's worrisome, and it really shows why it's important that we keep as much of the permafrost frozen as possible,» explains Kimberly Miner, a climate scientist at NASA's Jet Propulsion Laboratory at the California Institute of Technology in Pasadena ( California).
Permafrost covers a fifth of the Northern Hemisphere, supporting the arctic tundra and boreal forests of Alaska, Canada, and Russia for millennia. It serves as a kind of “time capsule”, storing — in addition to ancient viruses — the mummified remains of a number of extinct animals that scientists have been able to unearth and study in recent years, including two cubs of a cave lion and a woolly rhinoceros.
The reason permafrost is good storage is not just because it's cold; it is an oxygen-free environment into which light does not penetrate. But the rate of increase in daily temperatures in the Arctic is four times higher than in the rest of the planet, while the top layer of permafrost in the region is weakening.
To better understand the risks associated with frozen viruses, Jean-Michel Claverie, professor emeritus of medicine and genomics at the Aix-Marseille University Medical School in Marseille, France, tested earth samples taken from the Siberian permafrost to determine if they contained viruses. the particles are still infectious. He is looking for what he describes as «zombie viruses» — and has found some of them.
Clavery is studying a particular type of virus he first discovered in 2003. Known as giant viruses, they are much larger than the normal variety and are visible under a normal light microscope rather than a more powerful electron microscope, making them a good model for this kind 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 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 back to life.)
In 2014, Professor Claveri managed to revive a virus he and his team had isolated from permafrost, making it infectious for the first time in 30,000 years by introducing it into cultured cells. For safety reasons, he decided to study a virus that could only infect single-celled amoebae, but not animals or humans.
He repeated this in 2015, isolating another type of virus that also targeted amoebae. And in their latest study, published Feb. 18 in the journal Viruses, Claveri and his team isolated multiple strains of the ancient virus from multiple permafrost samples taken from seven different locations across Siberia, and showed that each could infect cultivated amoeba cells.
These latest strains represent five new families of viruses, in addition to the two he revived earlier. The oldest of these was nearly 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 below the surface. The most “young” samples found in the contents of the stomach and wool of the remains of a woolly mammoth, there are 27 thousand years.
The fact that the viruses that infect amoebas are still contagious after such a long time is indicative of a potentially bigger problem, Claveri said. He fears that people will regard his research as a scientific curiosity and not perceive the prospect of the return of ancient viruses to life as a serious threat to public health.
“We consider these viruses that infect amoebas as surrogates for all other possible viruses, which may be in the permafrost”, Claveri told CNN.
“We see 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 amoeba viruses are still alive, then there is no reason why other viruses would not still be alive and able to infect their own hosts”.
Traces of viruses have been found in the permafrost and bacteria that can infect humans.
A lung sample from a woman's body exhumed in 1997 from permafrost in a village 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 signatures of the smallpox virus.
An anthrax outbreak in Siberia that affected dozens of people and more than 2,000 reindeer between July and August 2016 has also been linked to deeper permafrost melt during exceptionally hot summers, allowing Bacillus anthracis spores to float to the surface from old burials. or animal carcasses.
Birgitta Evengaard, Professor Emeritus in the Department of Clinical Microbiology at the University of Umeå in Sweden, said there is a need for increased surveillance of the risk posed by potential pathogens from thawing permafrost, but warned against an alarmist approach.
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“You have to remember that our immune defenses have evolved in close contact with the microbiological environment,” said Evengaard, who is a member of the CLINF Nordic Center of Excellence, a group that investigates the impact of climate change on the prevalence of infectious diseases in people and animals in the northern regions.
“If the permafrost is hidden in A virus we haven't come into contact with for thousands of years, our immune defenses may not be strong enough, she said. — It is right to be respectful of the situation and take the initiative, and not just react. And the way to fight fear is to have knowledge”.