Viruses are between 27,000 to 48,500 years old and not dangerous, but researchers say thawing permafrost may one day release pathogens capable of infecting humans
Last fall, European researchers working with virologists and genetic scientists at the Aix-Marseille University in France reported having revived and characterized 13 previously unknown “zombie” viruses isolated from Siberian permafrost samples, including one that was almost 50,000 years old. This will be of particular interest to microbiologists and clinical laboratory managers since these organisms are new to science and may be precursors to infectious agents active in the world today.
The work of the European scientists demonstrates how advancements in genome sequencing and analysis of DNA data are becoming, faster, less expensive, and more precise. That’s good because the researchers warned that, should the permafrost continue to thaw, other previously dormant viruses could be released, posing potential risks for public health.
The scientists published their findings in the open-access journal Viruses titled, “An Update on Eukaryotic Viruses Revived from Ancient Permafrost.”
The pathogens isolated by the researchers are so-called “giant viruses” that infect Acanthamoeba, a commonly found genus of amoeba, and thus are not likely to pose an immediate health threat, the researchers wrote.
However, the scientists expressed concern. “We believe our results with Acanthamoeba-infecting viruses can be extrapolated to many other DNA viruses capable of infecting humans or animals. It is thus likely that ancient permafrost … will release these unknown viruses upon thawing,” they stated in their Viruses paper.
It’s unknown how long the viruses “could be infectious once exposed to outdoor conditions (UV light, oxygen, heat), and how likely they will be to encounter and infect a suitable host in the interval,” they added. However, “the risk is bound to increase in the context of global warming, in which permafrost thawing will keep accelerating, and more people will populate the Arctic in the wake of industrial ventures.”
“In nature we have a big natural freezer, which is the Siberian permafrost,” virologist Paulo Verardi, PhD (above), head of the Department of Pathobiology and Veterinary Science at the University of Connecticut, told The Washington Post. “And that can be a little bit concerning.” However, “if you do the risk assessment, this is very low. We have many more things to worry about right now.” Nevertheless, clinical laboratories may want to remain vigilant. (Photo copyright: University of Connecticut.)
Extremely Old, Very Large Viruses
The newly discovered viruses were found in seven different permafrost samples. Radiocarbon dating determined that they had been dormant for 27,000 to 48,500 years. But viruses contained in permafrost could be even older, the researchers wrote, as the time limit is “solely dictated by the validity range of radiocarbon dating.”
In their Viruses paper, the researchers noted that most of the 13 viruses are “at a preliminary stage of characterization,” and others have been isolated in the research laboratory “but not yet published, pending their complete genome assembly, annotation, or detailed analysis.”
“Every time we look, we will find a virus,” study co-author Jean-Michel Claverie, PhD, told The Washington Post. “It’s a done deal. We know that every time we’re going to look for viruses—infectious viruses in permafrost—we are going to find some.”
Claverie is a professor emeritus of genomics and bioinformatics in the School of Medicine at Aix-Marseille Université in Marseille, France. He leads a university laboratory known for its work in “paleovirology,” and in 2003, discovered the first known giant virus, dubbed Mimivirus. The research team included scientists from Germany and Russia.
According to CNN, unlike regular viruses that generally require an electron microscope to be viewed, giant viruses can be seen under a standard light (optical) microscope. Claverie’s laboratory previously isolated giant viruses from permafrost in 2014 and 2015.
Protecting Against Accidental Infection
To demonstrate the infectious potential of the viruses, the researchers inserted the microbes into cultured amoeba cells, which the researchers describes as “virus bait,” The Washington Post reported. One advantage of using Acanthamoeba cultures is to maintain “biological security,” the researchers wrote in their paper.
“We are using [the amoeba’s] billion years of evolutionary distance with human and other mammals as the best possible protection against an accidental infection of laboratory workers or the spread of a dreadful virus once infecting Pleistocene mammals to their contemporary relatives,” the paper noted. “The biohazard associated with reviving prehistorical amoeba-infecting viruses is thus totally negligible compared to the search for ‘paleoviruses’ directly from permafrost-preserved remains of mammoths, woolly rhinoceros, or prehistoric horses.”
The paper cites earlier research noting the presence of bacteria in ancient permafrost samples, “a significant proportion of which are thought to be alive.” These include relatives of contemporary pathogens such as:
How Dangerous are Ancient Viruses?
“We can reasonably hope that an epidemic caused by a revived prehistoric pathogenic bacterium could be quickly controlled by the modern antibiotics at our disposal,” the researchers wrote, but “the situation would be much more disastrous in the case of plant, animal, or human diseases caused by the revival of an ancient unknown virus.”
However, according to The Washington Post, “Virologists who were not involved in the research said the specter of future pandemics being unleashed from the Siberian steppe ranks low on the list of current public health threats. Most new—or ancient—viruses are not dangerous, and the ones that survive the deep freeze for thousands of years tend not to be in the category of coronaviruses and other highly infectious viruses that lead to pandemics.”
Cornell University virologist Colin Parrish, PhD, President of the American Society for Virology, told The Washington Post that an ancient virus “seems like a low risk compared to the large numbers of viruses that are circulating among vertebrates around the world, and that have proven to be real threats in the past, and where similar events could happen in the future, as we still lack a framework for recognizing those ahead of time.”
Anthony Fauci, MD, former Director of the National Institute of Allergy and Infectious Diseases (NIAID), responded to an earlier study from Claverie’s lab by outlining all the unlikely events that would have to transpire for one of these viruses to cause a pandemic. “The permafrost virus must be able to infect humans, it must then [cause disease], and it must be able to spread efficiently from human to human,” he told The Washington Post in 2015. “This can happen, but it is very unlikely.”
Thus, clinical laboratories probably won’t see new diagnostic testing to identify ancient viruses anytime soon. But it’s always best to remain vigilant.