The ancient thawed “zombie” virus of permafrost is still contagious

Large areas in Siberia, Alaska and Canada are covered with permafrost. But global warming, which is much more effective in the Arctic, is causing these permanently frozen soils to thaw more and more – with dire consequences: greenhouse gases such as methane or carbon dioxide (CO₂) can escape into the atmosphere and give global warming additional heat in a feedback loop.

However, the thawing soil not only releases greenhouse gases, but also plant remains and carcasses of animals such as woolly mammoths that have been kept in a freezer. And in these sometimes amazingly well-preserved remains are tiny stowaways: ancient, previously unknown viruses. Journalists and scientists like to call them “zombie viruses.”

A team led by French researchers Jean-Marie Alempic and Matthieu Legendre of the University of Aix-Marseille has now succeeded in detecting 13 such previously unknown viruses in permafrost samples – and reactivating them under laboratory conditions. One of the pathogens, that Pandora virus yedoomis probably the oldest virus discovered to date: it is believed to have survived in the ice for about 48,500 years, as the scientists write in their study published in the journal “Viruses”.

It’s not the first time zombie viruses have been detected in permafrost. As early as 2014, a French research team succeeded in creating the so-called giant virus Pithovirus sibericum use an amoeba to revive in the lab. And in 2017, Belgian biologists reanimated two viruses discovered in the faeces of a dead caribou. According to the researchers, they were intact and infectious even after 700 years in the ice.

All 13 newly discovered zombie viruses, which also came from samples from the Lena River and the Kamchatka Peninsula, were also contagious: they could infect amoebas of the genus Acanthamoeba castellanii infect. For safety reasons, these serve as bait for the pathogens, as all 13 viruses only affect unicellular organisms. The viruses studied belong to five virus genera not yet officially listed by the International Committee on Taxonomy of Viruses: Cedratviruses, Pithoviruses, Pacmanviruses, Megaviruses, and Pandoraviruses.

They are all gigantic viruses that are bigger than SARS-CoV-2, the coronavirus. They often also have a much larger genome – for example, the tupan virus, one of the largest known viruses, has 1.5 million base pairs, while the coronavirus gets by with 30,000 base pairs. Giant viruses are widespread in the environment, in oceans, fresh water and soil. They are also commonly found in permafrost.

The researchers cannot yet estimate how long the virus will remain contagious. Once they emerge from the deep freeze of the permafrost, they are exposed to outdoor conditions that are unfavorable to them – UV light, oxygen and heat. According to the study, it also depends on how likely they are to find and infect a suitable host in the meantime.

According to study leader Jean-Marie Alempic, such viruses from the thawing permafrost could pose a health risk. You see “traces of many, many, many other viruses”. There is a risk that there is a virus that can be dangerous for humans. “We’re not sure if they’re still alive. However, since the amoeba viruses are still alive, we don’t think there’s any reason why the other viruses shouldn’t be,” notes Alempic.

If a virus breaks free from the permafrost that humans haven’t encountered in millennia, our immune system may not be able to handle it properly. However, the research team admits that the research situation is still too sparse to make reliable statements. The risks posed by the melting permafrost need further investigation.

Albert Osterhaus, director of the Research Center for Emerging Infections and Zoonoses at the University of Veterinary Medicine in Hanover, provides some assurance. “The chance that such viruses lead to really big problems is small, but never 100 percent absent,” he says to Südwestrundfunk (SWR). On the contrary, live wildlife poses a greater threat, as evidenced by zoonoses such as the corona pandemic. The coronavirus probably jumped from bat to human.

Not only viruses, but also bacteria lurk in the ice. The scientists fear that the thawing of the permafrost will also release pathogenic microorganisms that are up to 120,000 years old and are related to current pathogens. You think of the anthrax pathogen Bacillus anthracisstreptococci or staphylococci.

The fear is anything but unjustified: there are indications that there are traces of it Bacillus anthracis caused an anthrax outbreak in Northern Siberia in 2016. The pathogen came from old graves or cadavers and was released when permafrost thawed in hotter-than-average summers. Several people got sick. Local reindeer deaths can also be attributed to this bacteria.

However, bacteria can – at least so far – be controlled quite well with antibiotics. Unfortunately, this is not the case with viruses, as the corona pandemic has also shown. Specific vaccines and medicines must first be developed for each new virus, which will not be available for some time.