The biggest virus ever discovered is awake—and infectious—after a 30,000-year nap buried deep in Siberian permafrost. Pithovirus sibericum, a member of a recently discovered class of giant viruses, was found 100 feet deep in the frozen ground. It only infects amoebas, but the researchers who uncovered it fear that plenty more ancient viruses are locked into the permafrost and could be unleashed as it thaws, Nature reports. The region is becoming both warmer and more accessible, which "is a recipe for disaster," one of the researchers says.
"If you start having industrial explorations, people will start to move around the deep permafrost layers. Through mining and drilling, those old layers will be penetrated and this is where the danger is coming from," he tells the BBC, warning that "if it is true that these viruses survive in the same way those amoeba viruses survive, then smallpox is not eradicated from the planet—only the surface." It's not clear, however, whether other viruses are as robust as the Siberian giant, which USA Today notes is as many as 20 times bigger than a typical virus but still dwarfed by a grain of sand. Explain the leaders of the team behind the discovery, "'Giant' viruses are loosely defined as the ones that you can see under a regular microscope." (Read more virus stories.)