Researchers have reported finding viruses frozen in Arctic soil since the early 2000s. Although some of these pathogens are tens of thousands of years old, that does not necessarily mean they are benign. A study published in PNAS suggests there may be reason to worry.
Mollivirus sibericum, the strain of giant virus covered in the PNAS paper, is in fact able to infect contemporary amoeba. However, it does not seem to pose a direct threat to humans. But this may not be the case for other types of ancient bacteria and viruses that could reappear as rising temperatures and melting ice thaw microorganisms that have been preserved across millennia, according to the abstract of the paper.
"The fact that two different viruses retain their infectivity in prehistorical permafrost layers should be of concern in a context of global warming," the authors wrote. "Giant viruses' diversity remains to be fully explored."