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The melting of the permafrost in lands around the Arctic Ocean has reawakened viruses frozen for tens of thousands of years. Their effects on people and animals are not yet known.

All around the northernmost reaches of the world's land masses, climate change is melting the permafrost. As icy soil that has been frozen for thousands of years begins to melt, the microorganisms within it are coming back to life.

Reawakening Of The Giant Viruses

The first of the viruses unleashed by melting soil was recognized by scientists about 2005. Russian scientists and guest researchers of the Russian Federation discovered a group of "giant viruses" in the ground that had not been active in tens of thousands of years.
These so-called giant viruses are so large that they can be seen under a regular microscope. They are even larger than some cells. The Pithovirus found in Siberia is nearly 1500 times larger than the smallest known viruses, and it has over 450 genes that can make 467 different proteins to take over its prey. The Pithovirus is a double strand of DNA, much like the DNA of a "cell only without the cell." It is not as active as the aptly named Pandoraviruses, found in the amoeba living in a contact lens of a German woman who had a stubborn eye infection, but it is larger than either the Pandoraviruses or the Megaviruses discovered in ocean waters off Chile.
These giant viruses found in Russia have a number of features that make them extremely durable. 
Their double helix of DNA circles around on itself, minimizing exposure to the elements. In that circle of DNA it forms a kind of crystalline structure. This helps it survive freezing and thawing. Unlike the virus that causes AIDS, the Pithovirus does not have a fatty outer layer that can be broken down as ice crystals melt.

Bad News For Amoebas, Not So Bad For Humans

The Pithoviruses, like the Pandoraviruses, multiply inside amoebas. Presumably, there were many amoebas in the deep, rich organic matter that has remained frozen since the beginning of the last Ice Age, which explains why these viruses have been found 100 feet (30 meters) down in melting bogs. The amoebas in turn feed on decaying plant matter, although some Siberian plants have been found to be similarly tough. A 32,000-year-old wildflower was regenerated in 2012, leading scientists to look for similarly old but surviving microbial life.
The good news about the virus discovered in 2014 is that it is not a danger to humans. It is only a danger to amoebas (although there is no way of knowing what the environmental effect would be if it should be reestablished in the wild). 
However, it turns out there are other giant viruses lurking in the melting permafrost, including a virus that may or may not be dangerous to human and animal life.
Dr Chantal Abergel, a scientist at the National Center for Scientific Research at Aix-Marseille University in France, announced the discovery of a giant Mollivirus at a depth of 98 feet (30 meters) in melting Siberian permafrost in September of 2015. Like three other viruses, this organism is thought only to infect amoebas, but there is a more sinister concern.
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  • Legendre M, Lartigue A, Bertaux L, Jeudy S, Bartoli J, Lescot M, Alempic JM, Ramus C, Bruley C, Labadie K, Shmakova L, Rivkina E, Couté Y, Abergel C, Claverie JM. In-depth study of Mollivirus sibericum, a new 30,000-y-old giant virus infecting Acanthamoeba. Proc Natl Acad Sci U S A. 2015 Sep 8. pii: 201510795. [Epub ahead of print] PMID: 26351664.
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