Scientists have discovered a 30,000-year-old virus that, while not a danger to humans, suggests viruses frozen in permafrost could emerge from a thaw intact, and potentially threaten our health.

According to a report published in the journal Proceedings of the National Academy of Sciences (PNAS), scientists “revived” a new type of so-called “giant virus” they found in the permafrost of Siberia.

The virus, named Pithovirus sibericum, is the latest of only three giant viruses ever discovered, the first having been found 10 years ago. It is also the largest of the three, at 1.5 micrometres long.

The giant viruses only infect amoeba, and pose no threat to human or animal health, the scientists say.

However, the successful revival of this latest virus, the scientists write, should raise concern that viruses that do infect humans or animals can also be preserved and once again become infectious.

“The revival of such an ancestral amoeba-infecting virus,” the researchers write, “suggests that the thawing of permafrost either from global warming or industrial exploitation of circumpolar regions might not be exempt from future threats to human or animal health.”