French scientists have revived a giant virus that had been locked in the Siberian permafrost for more than 30,000 years, a breakthrough that may serve as a warning that long-dormant, possibly harmful pathogens in frozen soil could be revived by Arctic drilling and global warming.

The scientists thawed the virus, Pithovirus sibericum, and watched it replicate in a culture in a petri dish, where it infected an amoeba, a simple single-cell organism, according to a study published Monday in the U.S. journal Proceedings of the National Academy of Sciences.

The study’s lead author told The Los Angeles Times that the discovery proves “that we could eventually resurrect active infectious viruses from different periods.”

“We know that those nondangerous viruses are alive there, which probably is telling us that the dangerous kind that may infect humans and animals — that we think were eradicated from the surface of earth — are actually still present and eventually viable, in the ground,” said microbiologist Jean-Michel Claverie of Aix-Marseille University in France.

The work detailed in the article shows that viruses can survive being locked up in the permafrost for extremely long periods, according to a statement released by France's National Center for Scientific Research.

"It has important implications for public-health risks in connection with exploiting mineral or energy resources in Arctic Circle regions that are becoming more and more accessible through global warming," it said.

"The revival of viruses that are considered to have been eradicated, such as the smallpox virus, whose replication process is similar to that of Pithovirus, is no longer limited to science fiction,” the statement continued. "The risk that this scenario could happen in real life has to be viewed realistically."

Scientists found the virus in a 98-foot-deep sample of permanently frozen soil taken from coastal tundra in Chukotka, near the East Siberian Sea, where the average annual temperature is minus 7.8 degrees Fahrenheit.

Radiocarbon dating of the soil sample found that vegetation grew in the area more than 30,000 years ago, when mammoths and Neanderthals walked the earth.

P. sibericum is, on the scale of viruses, a giant. It has 500 genes, whereas a flu virus has eight. It is the first in a new category of viral whoppers, a family known as Megaviridae, for which two other categories already exist.

The revived virus gets its name from "pithos," the ancient Greek word for "jar," since it has an amphora shape. It is so big that scientists can see it using optical microscopes rather than the more powerful electron microscopes usually needed.

Unlike flu viruses, P. sibericum is harmless to humans and animals because it infects only a type of amoeba called Acanthamoeba, the researchers said.

Al Jazeera and Agence France-Presse