Researchers have just discovered what is believed to be the newest representative of “giant viruses,” buried deep in the Siberian permafrost—where it has been for over 30,000 years. A team led by Jean-Michel Claverie and Chantal Abergel of Aix-Marseille University in France discovered the previously unknown virus, Pithovirus sibericum.
These “giant viruses” are still microscopic, but they are far larger than normal specimens, measuring 1.5 microns in length and .5 microns in diameter. By contrast, pandoraviruses, the largest viruses previously discovered, measure 1 micron in length and .5 in diameter. In contrast to most viruses, you can spot these under a microscope.They are also far more genetically complex. The newly discovered Pithovirus, for example, contains 500 genes. The Pandoravirus contains up to 2,500. The HIV virus contains only about 12.
When Claverie and Abergel exposed amoebas in their lab to the virus, they found it was still active.
Despite being embedded in ancient permafrost for tens of thousands of years, it still quickly infected the host cell. Giant viruses are hardier than normal viruses, which likely helped it stay intact for thousands of years.
“Among known viruses, the giant viruses tend to be very tough, almost impossible to break open,” the pair of researchers notes. “Special environments such as deep ocean sediments and permafrost are very good preservers of microbes [and viruses] because they are cold, anoxic, and in the dark.”
In the past decade, we’ve seen a massive boost in discoveries of these large, genetically complex viruses—suggesting that they can be much more intricate and more common than we initially thought. Some scientists suspect that different types of viruses have evolved separately, challenging the idea that all viruses evolved from one common origin.
The discovery of these frozen viruses also brings concerns about climate change. Could melting ice bring potential pathogens to Earth’s surface?
“If ‘viable’ [vital particles] are still there, this is a good recipe for disaster,” Claverie and Abergel note.
Still, the impact it would have on us is unknown. Only a very small proportion of the viruses on Earth can infect mammals and pose risks to humans. Disaster would be possible with the right conditions and DNA viruses can remain infectious for very long stretches of time. Claverie and Abergel are working to analyze the DNA content of the permafrost layers to determine the potential dangers.