By Deanna Altomara
A discovery of 28 new types of viruses in ancient ice has renewed fears that dangerous microbes might be hibernating in the permafrost, biding their time until increasing temperatures thaw the ice. Some are worried that diseases like smallpox or the 1918 flu might be preserved and poised to return. But how realistic is this fear?
Scientists disagree, and the lack of evidence doesn’t help. But we do have a few pieces of research that can help us keep the chances of a so-called “zombie pandemic” in perspective.
Most microbes are unable to survive the extreme cold. Ongoing research is attempting to study the few microbes that can, but this research is time and resource-intensive. Studying cold-tolerant microbes in the wild requires difficult and expensive expeditions to some of the most isolated spots in the world. Once there, scientists must be extremely careful that they don’t accidentally contaminate their specimens with modern microbes. And even if the samples aren’t contaminated, time has degraded the genetic material so much that only fragments remain. If there is not enough genetic material, it is impossible to accurately identify a microbe. And without a full genome, scientists stand little-to-no chance of resusciting anything.
Most viruses do not survive long outside of host cells, but some bacteria have been successfully cultured from ice. Most are psychrotolerants, which means they prefer warmer temperatures but can still be preserved for long periods of time in a cold environment. One such example is Carnobacterium pleistocenium, a rod-shaped bacterial species that had been buried under the Alaskan tundra near the end of the last Ice Age, about 32,000 years ago. The cells—which need neither light nor oxygen to survive—were revived as soon as they were thawed by the NASA scientists. Another example was even older—8 million years, to be exact. The scientists who uncovered this frozen bacteria from Antarctic ice published their research in the renowned journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), lending a certain credibility to their results. However, the bacteria grew at an extremely slow rate, leading the scientists to conclude that although reviving bacteria this old from ice is technically feasible, sustained growth is difficult and unlikely.
It’s unknown whether those few bacteria that do survive the icy conditions are able to thrive there, or if they had no choice but to hunker down into hibernation. There is currently no direct evidence that bacteria can be alive in the ice, but some studies have found pockets of carbon dioxide that could possibly have been produced by microbes.
While bacteria can survive in harsh conditions like those in the permafrost, such cases are extremely rare. But what about viruses? Most viruses do not survive long without a host cell. There have been many studies that have tried to find viable viruses in frozen victims of the 1918 flu in Alaska, but even the “successful” studies have only found fragments of the virus’ genetic material. In Russia, a project called Russia’s Virology and Biotechnology Center (VECTOR) has been investigating a graveyard of smallpox victims from the nineteenth century. Some people fear that these frozen bodies, which are beginning to melt in the face of increasing temperatures, might still harbor viables viruses. But so far, no one has been able to isolate the virus from these victims.
Again, while scientists are unlikely to find viable viruses in the ice, that does not mean it is impossible. Some viruses have been successfully revived, although none of these have been able to infect humans. Researchers were able to revive two viruses found in frozen 700-year-old caribou feces found more than a meter below the surface of an ice cap in Northwestern Canada. These viruses are thought to have infected plants and insects, respectively, and were probably part of the remains of the caribou’s ingested food (again, this was in feces), or insects. The genome was well-preserved, possibly due to the protection of the viral capsid. The capsid protects the virus’ genetic material, allowing many viruses to pass unharmed through the digestive system and remain infectious even in fecal matter. The same researchers could not find surviving genetic material from older samples, suggesting that the molecules had either degraded over time or been destroyed by the freeze/thaw cycle. The reconstituted viruses were able to successfully infect a plant, but the infection itself produced no visible symptoms.
In a similar finding in 2014, the married couple and famous biologists Jean-Michel Claverie and Chantal Abergel discovered a “monster virus” that had frozen for 30,000 years in the Russian permafrost. This virus is the largest in known existence. Claverie believes that other, more dangerous microbes may lurk within the ice. But others point out that Claverie’s harmless virus only infects amoeba, and is a far cry from frozen smallpox. Viruses and other microbes are abundant in nature, and most do not cause disease and are relatively harmless. If a microbe does survive in the permafrost, the chances that it will cause disease are fairly low.
But while all this evidence remains largely confined to high-tech labs, one has to wonder about the real-world implications of these findings. If most harmful bacteria can’t survive the ice, then how could anthrax have resurfaced in Russia? The key to anthrax’s longevity is in structures called spores. When ready to reproduce, some asexual organisms (including many plants and bacteria) form these tiny-but-tough cells, similarly to how most plants produce seeds. In the face of danger, spores can hibernate for thousands of years until environmental conditions become more favorable. In this case, the anthrax spores are helping the species to survive for long amounts of time in the ice, a situation that most organisms would find impossible to endure. Spores are not dead cells that come back to life–they are simply a hibernation stage in the normal life cycle of some organisms. Anthrax spores have been known to survive up to a century. So it seems like the ability to form spores, whether in the icy conditions of permafrost or a deep cave, could play a large role in determining which organisms are likely to survive these conditions. Yet in 2005, when the NASA scientists studied Carnobacterium pleistocenium, they found no evidence of spores.
So are we really at risk for a zombie virus apocalypse? While the chances are extremely low, it’s not an impossible scenario. But meanwhile, there are already health risks being caused by climate change. Air pollution, wildfires, floods, and more are changing disease patterns around the world.
So the threat of a zombie virus rising from the permafrost? That’s just the tip of the iceberg.
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