Mollivirus Sibericum is the fourth type of pre-historic virus found since 2003. Picture: J.M. Claverie/PNAS/CNRS

The researchers reported in flagship US National Academy of Sciences the discovery of Mollivirus Sibericum, the fourth type of pre-historic virus found since 2003.

Before waking it up in safe laboratory conditions, the French team will verify that the bug cannot cause animal or human disease, reported AFP. The prehistoric virus was found in the melting Siberian permafrost, said the respected news agency.

'A few viral particles that are still infectious may be enough, in the presence of a vulnerable host, to revive potentially pathogenic viruses,' warned researcher Jean-Michel Claverie.

Exploitation of oil or other mineral resources in these regions could unleash ancient viruses long dormant in the frozen permafrost, now melting due to climate change.

'If we are not careful, and we industrialise these areas without putting safeguards in place, we run the risk of one day waking up viruses such as smallpox that we thought were eradicated,' he claimed.

The same team discovered another giant virus, which they called Pithovirus Sibericum, at the same location in 2013, then revived it in a petri dish, reported AFP.

To the 'astonishment of scientists', these ancient specimens are 'complex genetically'. 'M. Sibericum has more than 500 genes, while another family of giant virus discovered in 2003, Pandoravirus, has 2,500. The Influenza A virus, by contrast, has eight genes,' revealed the AFP report.