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Discovery of a new type of giant virus more than 30,000 years old

​A new type of giant virus, dubbed “Pithovirus”, was discovered in the frozen soil of extreme northeast Siberia by researchers from the CNRS/Aix-Marseille Université, CEA-IRTVS, CEA-IG and the Russian Academy of Sciences. Buried in the ground, this giant virus (which is harmless to humans and animals) has survived more than 30,000 years of freezing. Although its size and amphora shape recall Pandoravirus, the analysis of its genome and its replication mode proves that Pithovirus is very different. This work brings the number of distinct families of giant viruses to three.

Published on 4 March 2014

​With the Megaviridae and3/4/2014 Pandoraviridae families, researchers had thought they indexed the diversity of giant viruses (the only viruses visible by light microscopy due to a diameter greater than 0.5 microns). These viruses, which infect amoebas in the genus Acanthamoeba, contain a very large number of genes as compared to common viruses (viruses like influenza or AIDS contain around ten genes). The size of their genome is comparable to or exceeds that of many bacteria.By studying a sample of frozen ground from extreme northeast Siberia (in the Chukotka Autonomous Region), the researchers were surprised to discover a new giant virus more than 30,000 years old (contemporary of the Neanderthal extinction), which they named “Pithovirus sibericum”. Its amphora shape, like Pandoravirus, first led scientists to believe that it was a new (but certainly very old) member of this family. However, further analysis of Pithovirus reveals virtually nothing in common with the previously characterized giant viruses. This therefore represents a new virus family, bringing the known number of families of giant viruses to three.

This discovery, coming so soon after that of Pandoravirus, also suggests that the diversity of viruses with an amphora shape may be as large as that of the “icosahedral” [1] viruses, which are among the most widespread today. This underscores how incomplete our knowledge of microscopic biodiversity remains, as soon as we explore new environments.Finally, this study shows that the virus can survive in the permafrost (a layer of permanently frozen soil in Arctic regions) on a near-geologic timescale, that is to say over 30,000 years (corresponding to the late Pleistocene).

This demonstration has important implications for public health risks related to the exploitation of mineral and energy resources in circumpolar regions, as global warming makes this increasingly feasible. The resurgence of viruses that are currently considered eradicated, such as smallpox (whose replication process is similar to Pithovirus) is no longer the realm of science fiction. The probability of such a scenario should be assessed realistically, and a metagenomic study of the permafrost, supported by the France-Génomique infrastructure (Investissement d’Avenir), is currently underway.

[1] Having the shape of a polyhedron with 20 sides.

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