Owing to global warming, a 30,000-year-old giant virus frozen in ice has been revived.
Scientists now warn that melting ice around the world could uncover new biological threats to human or animal health.
The research team incubated a 30,000-year-old Siberian permafrost core sample taken from coastal tundra in Chukotka, near the East Siberia Sea, with acanthamoeba castellanii -- a common host of giant viruses.
They found the presence of a giant virus particle known as a pandovirus, a type previously unseen.
The find could reveal viruses are far more diverse than previously thought -- and warn that ancient viruses could affect humans.
According to a statement issued by France's National Centre for Scientific Research (CNRS), the work shows that viruses can survive being locked up in the permafrost for extremely long periods.
The team of French and Russian researchers identified the virus by taking a culture of amoebas found in the permafrost.
It is so big - 1.5 millionth of a metre - that it can be seen through an optical microscope rather than the more powerful electron microscope.
"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," said CNRS in media reports.
The researchers warn that rising temperatures could release more viruses from areas such as Siberia.
They believe the finding could mean there are far more diverse types of virus than previously thought.