Researchers at the University of Aix-Marseille explain in a study published in the journal Viruses on Feb. 18, 2023, to warn against a risk they consider increasingly urgent, they have “resurrected” viruses that have been stuck in the permafrost for millennia. . The same team followed a similar process in 2014 and 2015.
The risk of spreading the virus
Some regions of the world, such as Siberia or Alaska, have permafrost: this is permafrost (also known by the English term “permafrost”). Climate change is causing it to thaw, which releases organic matter, which then breaks down into carbon dioxide and methane, greenhouse gases that in turn fuel climate change. “Some of this organic matter also consists of resurrected microorganisms (prokaryotes, single-celled eukaryotes) as well as viruses that have remained dormant since prehistoric times,” the study notes.
2016 was a clear illustration of this. Several cases of anthrax have been reported in humans (a 12-year-old child died) and in reindeer in Russia, although the disease has not claimed a victim in the region since 1941. Its reappearance was undoubtedly associated with abnormally high temperatures in the summer. , which melted the permafrost in which the carcass of a reindeer was imprisoned, carrying anthrax bacillus, the responsible bacterium whose spores are terrible.
Therefore, these organizations attract a lot of attention. But “it is reasonable to hope that an epidemic caused by a reanimated prehistoric pathogenic bacterium can be quickly controlled with the modern antibiotics at our disposal,” the researchers note. And add: “The situation would be much more catastrophic in the event of plant, animal or human diseases caused by the resurgence of an old unknown virus,” which would require “the development of very specific medical measures, such as new antiviral drugs or vaccines.” Viruses should be a priority, they said, while melting ice could also bring industries to the Arctic region, increasing proximity between humans and dormant pathogens.
Infectiousness still present after over 48,000 years
To emphasize the presence and contagiousness of these “zombie viruses”, the Marseille team isolated in seven regions of Siberia, “13 “Arctic” viruses, but only 7 are “prehistoric” because they are isolated from ancient permafrost and radiocarbon dated (carbon 14, editor’s note), Professor Jean-Michel Claverie, who led the study, explains to Sciences et Avenir. Among the 7 prehistoric viruses, there is a single isolate corresponding to a family of viruses that has already been isolated from the permafrost: Pithovirus mammonth. The rest belong to families that have already been described (Pandoravirus, Megavirus, Pacmanvirus), but none of the older isolates have been detailed. This is important because it demonstrates that long-term persistence in permafrost is not the preserve of any particular type of virus.”
In the laboratory, samples were brought into contact with cultures of amoebas of the genus Acanthamoeba for “resuscitation”. If the infectious particles are active, then they infect their host and cause his death. “This detection process is perfect because it simultaneously leads to the multiplication of viral particles (from 1 to 100 or 1000 for each infection), which are very few in the original sample,” Claverie assures.
The oldest of these “resurrected” viruses is over 48,500 years old and belongs to the species Pandoravirus Yedoma. Others, found in the digestive systems of fossilized wolves and mammoths, are over 27,000 years old. “This new article conclusively proves that viruses are capable of surviving tens of thousands of years (probably much longer than 50,000 years, which is the carbon-14 dating limit, but probably not the ‘survival’ limit) of viruses. freezing is not uncommon,” says Jean-Michel Claverie.
Fortunately, these viruses did not attack humans, but French scientists remain concerned. “Given the diversity of these viruses, both in their particle structure and in their mode of replication, it is reasonable to conclude that many other eukaryotic viruses (affecting cells with a nucleus, editor’s note) infect many hosts far beyond Acanthamoeba. can also remain contagious under similar conditions,” they note.
“It is very important to keep as much of the permafrost frozen as possible”
Thus, as the permafrost thaws, it can release other viral particles. It will then be necessary to take into account the duration of their infectivity in the open air and the likelihood of encountering the right host at the allotted time. “There are a lot of things going on with permafrost that are worrying, and (it) really shows why it’s important that we keep as much of the permafrost frozen as possible,” Kimberley Miner, a climate scientist at NASA’s Jet Propulsion Laboratory, told CNN. and author of a study published in Nature Climate Change on the subject. However, she called direct infection of humans with permafrost pathogens “unlikely.”
In an interview with Science et Avenir, Stephan Aris-Brosou, a University of Ottawa researcher and author of a study on increased risk of the virus spreading in the Arctic due to climate change, agrees that the study published in Viruses is interesting because “risks exist.” , and will increase. But his own research found “mostly plant and fungal viruses in modern samples from the high Arctic.” “Therefore, I see no reason for concern more than public (human) health issues, but these studies provide a new argument forcing us to reconsider our relationship with our planet and the consequences of climate change,” the researcher says.
In 2020, a workshop on the global health risks associated with microbial threats in the Arctic noted that while the potential risks may be low, “understanding and preparing for low-probability, high-consequence events is one of the hallmarks of strong public protection.” health.” strategy”.
Tiresome work
Doesn’t doing such an experiment in the lab increase the risk? For researchers at the University of Aix-Marseille and their colleagues, using the amoeba Acanthamoeba as a bait offers an important “biosecurity” benefit. “When we use Acanthamoeba cultures to investigate the presence of unknown infectious viruses in prehistoric permafrost, we are using its billionth evolutionary distance from humans and other mammals as the best possible defense against infection accidentally occurring to laboratory workers,” they assure.
As Professor Claverie himself admits, the characterization of this type of virus is also slow and tedious work. Therefore, the Laboratory of Genomic and Structural Information of the University of Aix-Marseille should, “probably let’s stop there with permafrost viruses.” Now he should be more interested in studying samples from Antarctica taken from the Ross Sea. .