"Zombie Viruses"
In February, an international team of scientists announced the successful revival of 13 different viruses stored in the permafrost for tens of thousands of years. "Hitek" tells why and how this experiment was necessary and whether ancient pathogens threaten people.Up to a quarter of the continental part of the northern hemisphere is covered by permafrost. It covers much of Siberia, the north of European Russia, Canada and Alaska. Because of a warming climate, the ground, which has been frozen for thousands of years, is gradually melting and releasing greenhouse gases.
In addition to the active emission, the soil contains microbes and viruses, which from prehistoric times have arrived in a "half-dead", dormant state. An international team of researchers from Russia, France, and Germany decided to test whether "unfrozen" viruses are capable of restoring activity and infecting modern organisms.
Why the experiment?
Climate warming is especially noticeable in the Arctic. Temperatures in this region are rising, according to various estimates, two or even four times faster than the global average. Researchers are recording the melting of permafrost at ever deeper depths. As a consequence, ancient organic layers that were frozen tens of thousands of years ago are warming and thawing. In the long term, this process may affect permafrost that was formed several million years ago.Permafrost thawing is not only connected with decomposition of ancient organics, which leads to emissions of carbon dioxide and methane into the atmosphere, further enhancing the warming effect. At the same time fixes the recovery of certain ancient microorganisms, which cause contamination of animals.
For example, in 2016 on the Yamal Peninsula, researchers recorded a mass outbreak of anthrax among reindeer. Then more than 2,500 animals were infected, of which almost one in nine died. Contact with sick reindeer also infected 36 people, one of whom died. The study showed that the infection was caused by strains of the bacterium Bacillus anthracis from an ancient burial ground. The pathogens were activated because of abnormal temperatures that caused the soil to thaw to a greater depth than normal.
Ancient layers more than a million years old may contain completely unknown pathogens. Although numerous studies have been devoted to the possibility of "reviving" bacteria from permafrost, the possibility of "zombie viruses" and its consequences remain poorly understood, scientists note.
What did the study show?
The analysis showed that, after thawing, the viruses retained the ability to infect the amoebas. They successfully penetrated the cells of the microorganisms, and the infection initiated active replication of the viral genome and the formation of new particles that were released and infected other microorganisms.The study confirms the ability of large DNA viruses that infect amoebae to remain infectious after more than 48,000 years spent in the deep permafrost. For three of the five genera studied, this is the first example of reactivation after freezing.
"We see these viruses infecting amoebae as surrogates for every other possible virus that might be lurking in the permafrost. We see traces of many, many, many other viruses. We know they are there. We don't know for sure if they are alive. But our premise is that if the amoeba viruses are still alive, there is no reason why other viruses would be dead and unable to infect their hosts." - Jean-Michel Claverie, co-author of the study in an interview with CNN.
The researchers note that in addition to revived viruses that infect amoebae, traces of many other species were found in samples from the evergreen, including some associated with known human pathogens such as poxviruses (smallpox viruses) and herpesviruses. Because of the high potential pathogenicity and risk of spread to humans, biologists have not tested whether these viruses have retained the ability to infect other organisms.
Many of the viruses that will be released as the ice melts will be completely unknown. It is not yet known if and how infectious they will be when exposed to light, heat, and oxygen from the outside environment. But the results of the experiment suggest that at least some of them will be able to be transmitted to humans, and that humans may not be immune to such pathogens.
Given the inevitability of global warming, scientists urge caution when mining in permafrost areas, and note the need for further research to minimize the risk of an epidemic caused by unknown viruses.