Pathogens in the Permafrost: Could Melting Ice Unleash Ancient Diseases?

How climate change is unearthing microbes from thousands — if not millions — of years ago.

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It’s like a scene from an apocalyptic movie: an ancient virus reemerges from the polar ice caps, unleashing a pandemic that kills millions, causes mass panic, and destroys life as we know it. Some people fear that this is a scenario that could be closer than we think. But do we really have to worry about an epidemic emerging from the icy vaults of pre-history?

Several years ago, an investigation into the frozen landscape of Tibet’s Guliya ice cap unearthed 28 types of never-before-seen viruses–a startling discovery that has reignited the scientific controversy over whether climate change could release “zombie pathogens” from melting permafrost.

In this particular , scientists from the US and China sampled two ice cores from 51 meters under the surface of the Guliya ice cap in the northwestern Tibetan Plateau. The ice samples, which ranged in age from 520 to 15,000 years old, contained 33 distinct viral populations. These viruses were associated with certain bacterial groups, which were probably the main hosts for viral infection. The study was published without undergoing , so while the preliminary research is fascinating, the results should be taken with caution.

Permafrost is ice that encases what used to be (think 35,000 years ago) marshy grasslands. Every summer, it partially thaws, and each winter it refreezes, a cycle that has continued for thousands of years. Some microbes can survive near the surface of the permafrost, the partially-thawed area known as the ‘active zone.’ But with climate change, the active zone is pushing deeper into the, warming up ancient pockets of frozen soil, and also stretching farther north. The permafrost contains frozen soil debris, plants, animals–even perfectly preserved human bodies. One team of scientists even found seeds that had been frozen solid for thousands of years, and still after being warmed and planted.[1] The permafrost harbors a rich archive of the earth’s history, with many examples of organic matter that never decomposed. But as the ice melts, these ancient remnants are beginning to rot, releasing gas into the atmosphere and actually accelerating the process of climate change.

The threat of a “zombie virus” seemed to become a living nightmare in the summer of 2016, when an anthrax outbreak emerged in Siberia. Anthrax is a disease caused by the bacteria . It lives in soils around the world, where it is occasionally disturbed and triggers deadly outbreaks among both animals and people. In the early twentieth century, over a million reindeer died of anthrax, and were often buried in shallow graves with 7,000 burial grounds across . There was a Russian campaign to vaccinate reindeer, who were most likely to catch the virus and pass it on to humans. This campaign was successful; there were no outbreaks for decades and, assuming that anthrax had been eliminated from the area, deer vaccination stopped in 2007.[2] But anthrax had not disappeared–it was simply hibernating in the permafrost.

In 2016, an unusually warm summer thawed the permafrost, caused an outbreak of anthrax that and hospitalized dozens more.

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.[3]

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 , 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.[4] 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 , 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.[5]

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 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.[3] 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 melta 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.[6]

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.[3]

In a similar finding in 2014, the married couple and famous biologists Jean-Michel Claverie and Chantal Abergel discovered a that had frozen for 30,000 years in the Russian permafrost.[7] 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 . 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 , they found no evidence of spores.[4]

In 2023, Russian scientists announced that they had resurrected roundworms that had laid beneath Siberia since the last Ice Age. The frozen worms, which were smaller than pencil tips, were found in a fossilized gopher burrow buried 130 feet deep within the permafrost. Permafrost is soil that has been frozen for a long time, in some cases thousands of years. Because it is so cold, it is great for preserving the remains of plants and animals.

The researchers took the soil samples to the lab, where they identified the creature as a type of roundworm. Roundworms are simple, tube-shaped creatures that are found all over the world. Many roundworms are good for the soil, but some can cause diseases.

When researchers put the worms in water, something miraculous happened: the worms woke up. They flourished in the lab’s carefully monitored conditions, giving birth to over a hundred generations of new worms.

These worms, now named Panagrolaimus kolymaenis, have the rare ability to enter a near-death state called cryptobiosis. During this time, the worms — and all of their life functions like eating and growing — slow down to a near standstill. The ability allows them to survive unthinkable conditions like extreme cold, extreme heat, or lack of oxygen.

Other creatures can also enter cryptobiosis. For example, some bacteria, including anthrax, form spores-tiny, hibernating cells that can survive for untold amounts of time in extreme conditions. However, it’s rare to find examples who have survived since ancient times.

That doesn’t mean it hasn’t happened. Other researchers claim to have revived 30,000-year-old and 48,500-year-old viruses from Russian permafrost, a 42,000-year-old bacterium from the Alaskan tundra, and an 8-million-year-old bacterial spore from Antarctic ice. Most of these germs don’t infect humans, but more simple creatures like amoebas.

As the climate warms, that permafrost is melting at unprecedented rates. It currently covers large areas of the Arctic and surrounding areas, often far beyond the watchful eyes of public health officials. Some scientists, like Dr. Teymuras Kurzchalia, who helped run the worm study, fear that some germs might be able to survive in the wild and cause outbreaks.

Luckily, scientists say that the risk for outbreaks caused by germs in melting ice remains low. The environment is filled with microbes, and most are harmless or even helpful. In fact, very few infect humans at all. Meanwhile, it is still rare for germs to survive in the ice, let alone the thawing process. But just in case, some researchers, like Birgitta Evengård of Umea University, want better resources and disease surveillance systems in the far North.

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 . Air pollution, wildfires, floods, and more are changing disease patterns worldwide.

So the threat of a zombie virus rising from the permafrost? That’s just the tip of the iceberg.

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Originally published at on July 31, 2023.