Jean-Michel Claverie and Chantal Abergel led a team of scientists into Siberia to look for frozen viruses. A soil sample they took from the permafrost 100 feet underground has yielded a previously-unknown virus that will still infect cells, even after being frozen for somewhere between 34,000 and 37,000 years! The virus, named Pithovirus sibericum, is also extremely large: 1.5 micrometers, which can be seen with a regular microscope. That’s up to 100 times larger than the average virus.
It poses no danger to humans, because it exclusively infects single-celled organisms called amoebae—something the scientists discovered when they revived the microbe from its inert virion form by warming it up and putting it in a petri dish with live amoebae. Once revived, the virus entered the amoebae cells, hijacked the cells' metabolic machinery to create many copies of itself, and split the cells open, killing them and freeing itself to infect further cells.
Previously-known giant viruses also infect amoebae, likely because of how easy it is to enter them. Amoebae feed through phagocytosis, using their cellular membranes to engulf particles and organisms; for a giant virus to get inside an amoeba, all it has to do it let itself be engulfed. Because most human and other animals cells don't engulf particles in this way, viruses that infect us generally have to use more complex entry methods, which prohibit such an enormous size.
How can a virus stay dormant so long and come back to life? Because viruses are not exactly what we normally call “living.” They exist on the line between how we define living and non-living things. They can reproduce, but they do not have their own equipment to do it -rather, they must hijack a living cell in order to harness the cell’s energy and replicate their DNA. Viruses: truly weird and getting weirder. And even though this “new” old virus cannot infect humans, who is to say there aren’t other viruses that can, frozen in the earth, just waiting to re-activate someday? Read more about the frozen giant virus Pithovirus sibericum at Smithsonian.
(Image credit: Julia Bartoli and Chantal Abergel, IGS and CNRS-AMU)