Climate change: The real danger of thawing Permafrost

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Researchers have shown that it is possible to revive “zombie viruses” that have been frozen in the ground in Russia for up to a whopping 48,500 years. In their study, environmental virologist Professor Jean-Michel Claverie of the Aix-Marseille University and his colleagues identified more than a dozen new microbes, although they were careful to only revive ones incapable of infecting humans. However, they cautioned, the findings highlight a potential health risk from climate change — that the thawing of once-frozen ground across parts of the Northern Hemisphere could unleash deadly new viruses that might even trigger a pandemic.

The researchers wrote: “One quarter of the Northern hemisphere is underlain by permanently frozen ground, referred to as permafrost. Due to climate warming, irreversibly thawing permafrost is releasing organic matter frozen for up to a million years.”

Most of this material, they noted, decomposes into carbon dioxide and methane, further enhancing the greenhouse effect. However, they added, “Part of this organic matter also consists of revived cellular microbes […] as well as viruses that remained dormant since prehistoric times.

“While the [scientific] literature abounds on descriptions of the rich and diverse prokaryotic microbiomes found in permafrost, no additional report about ‘live’ viruses have been published since the two original studies describing pithovirus (in 2014) and mollivirus (in 2015).”

These reports — also by Prof. Claverie and his team — concerned Mollivirus sibericum and two species of the giant virus of the genus Pithovirus (P. sibericum and P. massiliensis), both of which were recovered from a 30,000-year-old ice core from Siberia.

The scarcity of studies on such viruses, the team continued, “wrongly suggests that such occurrences are rare and that ‘zombie viruses’ are not a public health threat.”

In their new study, Prof. Claverie and his colleagues studied samples from seven different ancient Siberian permafrost soils, as well as one sample from the Kamchatka Peninsula in the Russian Far East, and one modern sample from the Lena River in Yakutsk — the coldest city on Earth which is located on continuous permafrost.

Samples were taken not only from soils and a melting ice wedge, but also from the stomach contents of a woolly mammoth dating back around 28,600 years and the intestines of a fossil wolf dated back more than 27,000 years.

The team report successfully characterised 13 new viruses from five different clades. These included cedratvirus, megavirus, pacmanvirus, pandoravirus and pithovirus.

The oldest microbe — a pandoravirus collected from a sample taken 53 feet below a lake at Yukechi Alas, Siberia — is estimated to have been frozen for a whopping 48,500 years.

In order to ensure their research would pose no health risk, the team only looked for viruses capable of infecting a microscopic, single-celled organism called acanthamoeba — one of the most common amoeba in soils and freshwater.

The team said: “A decisive advantage of our approach was to choose Acanthamoeba spp. as a host, to act as a specific bait to potentially infectious viruses, thus eliminating and risk for crops, animals or humans.”

They added: “We are using its billion years of evolutionary distance with humans 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 biohazard associated with reviving prehistoric amoeba-infecting viruses is thus totally negligible, compared to the search for ‘palaeoviruses’ directly from permafrost-preserved remains of mammoths, woolly rhinoceros, or prehistoric horses.”

Such “risky projects”, the team note, are presently being undertaken in the State Research Center of Virology and Biotechnology VECTOR — often called the “Vector Institute” in Koltsovo, Novosibirsk Oblast, Russia.

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Regardless of the wisdom of the Vector Institute’s experiments, long-frozen viruses may still end up presenting a threat as global warming thaws out the world’s permafrost.

Dr Claverie and colleagues warned: “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. How long these viruses could remain 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 — is yet impossible to estimate.

“But the risk is bound to increase in the context of global warming when permafrost thawing will keep accelerating, and more people will be populating the Arctic in the wake of industrial ventures.”

A preprint of the researchers’ article, which has not yet been peer-reviewed, can be read on the bioRxiv repository.

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