by A group of scientists led by Jean-Michel Claverie has analyzed soil samples from the Siberian permafrost in search of so-called zombie viruses, which have been dormant for thousands of years, and which could be brought back to life by global warming.
The film industry is fascinated by dystopias and post-apocalyptic scenarios, and many film or television productions are based on the possibility of microorganisms appearing out of nowhere to attack, decimate or directly destroy humanity. Invariably, these scenarios feature a terrifying landscape and a handful of survivors fighting mutants, zombies, or other survivors on a devastated planet.
The last of these productions is the series The last of Us. Although it has the fungus as a protonist Cordyceps unilateralis and not a virus, in its first scene a scientist asks the audience of a 1968 television program what would happen if the temperature of the planet “raised slightly”.
Permafrost, the frozen ground layer… but not
The word permafrost comes from English, from permanentpermanent, and frost, Frost. For something to be considered permafrost, it has to stay frozen for two consecutive years. In addition, most of it is in the northern hemisphere, and it accounts for almost a quarter of the earth’s land area. It is mainly concentrated in the Arctic region, particularly in Siberia, Alaska, parts of Canada and Greenland, although it is also found in the Pyrenees, for example.
The permafrost has two layers, the active surface layer or mollisol, which reaches a depth of one meter and often thaws, and the pergelisol, the deeper frozen layer, which can reach up to 1,500 meters in northeast Siberia.
permafrost
Dr. Jean-Michel Claverie explains in an article for ThinkGlobalHealth that despite popular belief that permafrost is frozen, “regions north of the Arctic Circle are not permanently snow-covered frozen expanses,” and in some points, “although the average annual temperature there does not exceed -10°C, it remains above zero from June to September, occasionally reaching 30°C.”
Summer temperatures cause a vegetation cover to grow each year in the active layer, made up of a diverse fauna and a complex microbial system. In this cycle, this layer of living matter breaks down and refreezes. The ground is permanently frozen, but not covered with ice or snow.
Explosive cocktail: global warming, permafrost and carbon
These permafrost features that had been stable for 400,000 years in the Arctic are now changing. During the 21st century there will be an average increase in the earth’s temperature of 1.5°C with respect to the pre-industrial era, but it is that the Arctic is warming two to three times faster than temperate regions.
Summer mollisol melt will reach ever greater depths and permafrost cliffs in coastal or river areas will erode more rapidly. This will increase the release and reactivation of permafrost microbes, including ancient ones from the late Pleistocene (of the last 100,000 years).
Also, the amount of carbon trapped in permafrost is about twice that found in the atmosphere. As permafrost is lost, decomposed organic matter is released in the form of carbon dioxide and methane, the two main greenhouse gases, thus again contributing to global warming (which again will contribute to permafrost loss).
In turn, the melting ice has made Siberia’s northern coast more accessible by sea, so the area is increasingly attracting more mining companies, the oil and natural gas industries. On the one hand, these industries may accelerate the destruction of permafrost, and on the other hand, the population of hitherto little-inhabited areas will slowly increase. This could increase the risk of spreading a potential virus that affects humans.
Microorganisms that come back to life
Two 2014 and 2015 investigations by Jean Marie Claverie, the latter in collaboration with his wife, Dr. Chantal Abergel, have already “resurrected” two viruses trapped in the Siberian permafrost for 30,000 years. In fact, his work gave rise to a new field of study in evolutionary biology, paleovirology.
The two viruses discovered by these studies, Pithovirus sibericum and Mollivirus sibericumare what are known as “giant viruses”, because they are so large that they can be seen under a normal microscope.
A new study published in February 2023 and led by Claverie revived seven new amoeba viruses, hitherto unknown to humanity, but which have now made their way to the outside world from melting permafrost.
Claverie’s team analyzed soil samples taken from the Siberian permafrost to see if there were infectious viral particles in viruses nearly 50,000 years old. The researchers used amoebas as bait, and the ancient viruses soon infected these lab-grown amoeba cells.
For safety, the viruses used in these investigations were carefully chosen among those that cannot attack humans or animals.
Do we have to worry about permafrost viruses?
The revival of viruses so ancient that they infect amoebas suggests that the thawing of the permafrost, whether due to global warming or the industrial exploitation of circumpolar regions, could pose future threats to human or animal health.
The idea behind these investigations might seem alarming, but in 2016 an anthrax outbreak killed thousands of reindeer, sickened humans, and even killed a child in Yamalo Nenets, in the Siberian tundra. The heat wave that year affected the melting of the permafrost and released ancient spores from the Bacillus anthracis, probably from the frozen carcass of some infected reindeer. It had been 75 years since there had been an outbreak, specifically since the last reindeer immunization.
Claverie’s concern is that his research is not taken into account beyond a curiosity, since the permafrost is a huge reservoir, something like a snow globe that contains microorganisms that humanity has known and against which it can at least fight, and others that are much older and that, as their study shows, may be viable. The consequences of the balloon breaking and its contents being released could be disastrous.
REFERENCES
An update on eukaryotic viruses revived from ancient permafrost
In-depth study of Mollivirus sibericuma new 30,000-y-old giant virus infecting Acanthamoeba
Reindeer Anthrax in the Russian Arctic, 2016: Climatic Determinants of the Outbreak and Vaccination Effectiveness
Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology
Zombie viruses from the Arctic
