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Are extinct viruses coming back thanks to climate change?

Scientists discovered and revived a Stone Age virus frozen in the Siberian permafrost for 30,000 years.
Scientists discovered and revived a Stone Age virus frozen in the Siberian permafrost for 30,000 years.

As many continue to debate the existence and causes of global warming, scientists around the world -- who are in near-lockstep agreement about both the existence and causes of climate change -- continue to discover the possible ramifications of warming. Mass extinctions of plant and animal species, rising sea levels and an increase in number and severity of storms all make the cut. Now we can add one more possible consequence of a warmer planet, and it's a frightening one at that: the resurrection of viruses that were long thought extinct.

In what reads like the screenplay for a "Jurassic Park"-type disaster film, a virus frozen for 30,000 years in the Siberian permafrost has been discovered, resurrected and used to infect amoebas in a lab. As dramatic as that sounds, don't panic -- yet. Scientists responsible for the discovery stress that this new virus cannot be transmitted to humans -- and so far there is no evidence that the permafrost is hiding anything that could harm either humans or larger animals. But take a look at the key phrase in that last sentence: "at this point." That's where the climate change discussion comes in [source: Ghose].

According to the report from scientists at the National Centre of Scientific Research at the University of Aix-Marseille in France, the virus discovered in the permafrost is a type of "giant" DNA virus -- a type of virus that, unlike a regular virus, is visible under a microscope. Pithovirus sibericum, as this new virus is called, is the third giant virus to be discovered. It is also the largest and oldest -- as far as we know [source: Legendre].

The first giant DNA virus to be found, the Acanthamoeba polyphagamimivirus (APMV), was discovered in the early 1990s but not described until the early 2000s. Since then, scientists have discovered other viruses similar to the APMV, initially leading researchers to believe that all giant viruses would be part of this family [source: Von Etten].

Then several years later, Pandoravirus salinas, a completely different virus unrelated to the APMV family, was discovered. While Pandoravirus shows different characteristics from the mimivirus, they can both infect amoebas. The discovery of Pandoravirus made scientists realize that giant viruses are much more diverse than originally thought [source: Smith].

Which brings us back to the latest discovery: Pithovirus sibericum, the first virus in yet another new family. This third giant DNA virus to be discovered has scientists speculating that they've just scratched the surface of what may be whole host of giant viruses hiding in plain sight around the world. For instance, while AMPV was discovered in a water cooling tower in England and Pandoravirus was first discovered off the coasts of Chile and Australia, Pithovirus was found in the Siberian permafrost [sources: Von Etten; Smith; Legendre].

The permafrost may be a better place to look for more viruses than out in the open. The northeastern Siberian permafrost is one of the best geographic regions to look for surviving ancient microorganisms thanks to its neutral pH, among other qualities. Pithovirus was collected in 2000 from permafrost in Chukotka, Russia, a spot in the far northeastern part of the country not far from western Alaska. The virus was collected from a horizontal sample taken from a steep bank 76 feet (23 meters) above the Anui River and radiocarbon dated to 30,000 years ago. The layer had never thawed in all that time [source: Ghose].

In the lab, the permafrost was added to amoebas -- single-celled organisms that thrive in damp environments or as parasites -- to see if it contained infectious agents. This is a much safer way to explore the properties of permafrost than exposing it to humans, as scientists confirmed when the amoebas began to die. The scientists discovered a virus multiplying inside the amoebas; following the viral infection, the amoebas soon exploded and died.

The researchers were quick to reassure the public that this giant virus, despite sounding like the harbinger of doom in a sci-fi flick, could not infect humans or animals. However, they did express some concerns about the discovery.

Although Pithovirus is the first of a new family, its genome structure and replication cycle are similar to other large (but not technically "giant") DNA viruses, many of which are human or animal pathogens -- meaning they can cause disease in humans or animals. Pithovirus could just be the tip of the iceberg, so to speak, of viruses hidden in permafrost. So, while Pithovirus specifically doesn't worry scientists, its unmet cousins, aunts and uncles sleeping in the ice may not be as benign [source: Sirucek].

Let's tie this all back to climate change. The global climate continues to warm: From February 2014 through February 2015, nine of the 12 months were either the warmest or second warmest on record [source: NOAA]. The permafrost will continue to melt, revealing secrets -- good, bad and in between -- that have been hidden within for thousands of years.

This is a potential problem in particular in the Russian Arctic, where climate change is more pronounced than it is in other parts of the world. The average temperature across the globe has increased 1.3 degrees Fahrenheit (by 0.7 degrees Celsius) in the last hundred years, while the average temperature of the surface layer of permafrost has increased by 5 degrees Fahrenheit (3 degrees Celsius) and has diminished in depth by 7 percent [source: NOAA]. Add to this the fact that rich mineral resources and oil reserves in the arctic region are being increasingly mined and drilled, which also causes the melting of permafrost, and you can begin to understand why it becomes urgent to look at the possibility that infectious viral pathogens slumber in ancient layers of permafrost.

Along with oil drillers, researchers continue to mine the permafrost, pointing out that isolating and reviving ancient amoeba-infecting viruses from the frozen tundra is an inexpensive and safe way to assess the threat posed by these and other as-yet-undiscovered giant DNA viruses.

While the idea of bringing a 30,000-year-old virus back to life and destroying some poor amoeba is pretty cool, at least in the sci-fi world, does it pose a threat? Outside of the movie world, what are the chances that some Neanderthal-killing bug that modern folks have no natural immunity to and little ability to fight off will surface to wreak havoc on humanity?

Well, as some have said, the probability has gone from zero to not-zero. Translated: It's not hugely likely. However, as recently as 2005, it didn't seem likely that Pithovirus -- or anything similar -- could exist in the modern world. If nothing else, the discovery and rebirth of these "extinct" viruses show that they may be anything but. Given the admittedly small likelihood of a resurgence of ice-age viruses, or even newer ones that were thought to have been eradicated, such as smallpox, researchers nonetheless recommend vigilance and a stock of vaccine be kept on hand, just in case [source: Sirucek].

Meanwhile, as of 2015, work in the permafrost continues -- not, as researchers say, because they are looking to revive viruses that might pose a threat to humans or animals, but because they want to assess the possible dangers. (Or maybe they're working on a cool sci-fi screenplay and don't want anyone to know just yet).