As the planet warms and the ice thaws, scientists warn we could see the re-emergence of ancient pathogens currently unknown to science. These viruses, which have laid dormant and locked away in glaciers and permafrostpermanently frozen soilfor hundreds if not thousands of years, could "wake up," researchers have said.

Earlier this year, scientists analyzing two ice core samples from Guliya ice cap, Tibet, identified several of such viruses. One of the core samples dated back 520 years, while the other held sediments locked away 15,000 years ago. Four of the virus generathe taxonomic rank between species and familywere already known, but 28 had never been seen before.

The study authors say the research provides evidence of an "ultra-clean" method of microbial and viral samplingone clean enough to extract virus from the glacier unharmed and uncontaminated

Yet it also reveals a chapter in the planet's biological history, exposing some of the microbes that inhabited the soil hundreds and thousands of years ago that could, theoretically, re-emerge as the ice melts.

The study's authors warn that ice melt "will release glacial microbes and viruses that have been trapped and preserved for tens to hundreds of thousands of years."

This melt could destroy microbial "archives" that may help us understand the Earth's climate regimes in the past. "However, in a worst-case scenario, this ice melt could release pathogens into the environment," they add.

Their research is in the preprint stage, meaning it has not been reviewed by a panel of experts to confirm the findings. As such the results should be viewed with caution. It is also not clear how complete or infectious these viruses would be post-thaw. However, scientists have previously revived viruses that have been dormant for thousands of years, suggesting it is at least a possibility.

Could ancient viruses pose a public health risk? "Maybe," Jean-Michel Claverie, Professor of Genomics and Bioinformatics at Aix-Marseille University in France, who was not involved in the Tibetan glacier study, told Newsweek.

"They could be ancient viruses that we already knowsuch as smallpox virusthat we wrongly think were eradicated," he added.

"There also could be viruses that caused animalor humanextinctions in the past, and that modern medicine is not aware of. The same is true of pathogenic bacteria, such as those causing anthrax."

Claverie's research has shown that viruses can "survive" tens of thousands of years"since the Neanderthal era"unperturbed, provided the conditions are right. In 2014, he co-authored a paper describing a 30,000-year-old "giant virus" extracted from Siberian permafrost. Out of the permafrost and in the lab, it revived, becoming infectious after a millenia spent dormant.

Giant viruses like these get their name because they are so large, relatively-speaking, they can be easily viewed under a light microscope. While an average virus can be as small as 20 nanometers, a giant virus cannot fit through a hole 200 nanometers or smaller.

The one discovered in 2014 has been named Pithovirus sibericum; "pithos" being the name of a large storage container used by the Ancient Greeks. Since then, the team has discovered at least one other ancient virus, Mollivirus sibericum, found in the same 30,000-year-old ice sample.

Fortunately, both attack amoebassingle-celled organisms with the ability to shape-shiftand not animals or humans. This means its resurrection did not pose a public health risk. However, researchers say their existence raises the question of what other, more deadly pathogens maybe waiting in the permafrost, ready to activate.

The virus' impressive longevity stems from the fact that technically, they are not living things. To activate and reproduce, they must penetrate the cell of a living organism. Outside of a cell, they are metabolically inert particles called virions, which can be imagined as seeds to the activated virus, said Claverie.

This means they cannot die in the typical sense. Virions can either be infectious and ready to "germinate" or inactivated, too damaged to infect or germinate.

This deterioration process can take place rapidly outside of a celllight, for example, is incredibly damaging to the virus DNA or RNA. The loss of moisture can also cause damage to the point of inactivation.

However, if the conditions are conducive to their "survival," they can remain infectious for extended periods of time.

"UV light, oxygen, high temperature is bad, cold and darkness is better, cold, darkness and no oxygen [anoxic] is best," said Claverie. That makes permafrost and deep ocean sediments cold, dark, anoxicexcellent environments for microbes like viruses.

The increased interest in ancient viruses and ice-locked microbes has not only been spurred by Claverie and others' research, but by scientific data highlighting a rapid increase in ocean warming and ice melt.

We know the Arctic is warming twice as fast as the rest of the world, while ice sheets across the planet have shown consistent thinning linked to climate change and changing weather patterns.

The last two months have seen Antarctica break its record for ice meltit was reported that 15 percent of the continent's surface melted on Christmas Eveand record warm water under its most precarious glacier, the Thwaites glacier.

Smaller glaciers are also feeling the heat. Last year's Intergovernmental Panel on Climate Change (IPCC) report found that glaciers in Europe, eastern Africa and elsewhere could lose more than 80 percent of ice mass by the end of the century. Meanwhile, permafrost in the Arctic circle is thawing at a rapid pace.

Permafrost covers 24 percent of the Northern Hemisphere, an area equivalent to 9 million square miles, according to Columbia's Earth Institute. Scientists predict that even if we were to limit warming to 2 degrees Celsius above pre-industrial levels, we would eventually lose 40 percent of that.

As the permafrost thaws, these snow-covered landscapes are turning from carbon sinks into carbon emitters with the potential to release vast amounts of greenhouse gas and cause the infrastructure it supports to crumble.

This warming could also unlock viruses currently hidden in the ice and permafrost. Although the likelihood of these ancient or historic viruses reactivating remains relatively unknown.

"This is a new area of research," Christine Kreuder Johnson, Professor of Epidemiology at University of California Davis, School of Veterinary Medicine told Newsweek. "I would say very exciting. [There is] not a lot known."

One of the key things to consider when investigating ancient viruses like those found in the Tibetan glacier, Kreuder Johnson explained, is the state of the virusis it whole or is it fragmented? Because this will affect its ability to infect and therefore, the threat it poses to human health.

"Viruses detected only pose a risk if they're completely whole and can regrow," said Kreuder Johnson.

Some microbes are hardier and, therefore, more likely to be infectious than others. Take, for example, spore-generating bacteria like anthrax.

Anthrax is not technically an ancient diseaseit can be found in soil across the worldbut it has been called a "zombie pathogen." This is because it can lie latent for centuries before reactivating and triggering new outbreaks.

In 2016, a 12-year-old boy died and dozens more were hospitalized in Salekhard, northeast Russia, with anthraxdubbed the "Siberian plague." The outbreak is believed to have originated from the diseased remains of humans and animals buried in permafrost 75 years earlier, later exposed after a heat wave caused the ice to thaw.

It is thought that reindeers came into contact with the remains, spreading the disease to humans. The boy was one of a number of nomadic herders affected, Newsweek reported at the time.

Medical experts cited climate change as a factor in the outbreak, pointing to the abnormally warm weather that had caused the permafrost to thaw. This is supported by studies that suggest rising temperatures could lead to similar incidents in the future.

Elsewhere, there have been reports of researchers contracting diseases after coming into contact with the frozen carcasses of diseased animals.

Michael Zimmerman, a paleopathologist at the University of Pennsylvania, told NPR he developed seal fingera bacterial infection that typically affects the fingers and hands of seal hunterswhile completing research on animals buried in the permafrost for decades. The diagnosis was not confirmed but matched the symptoms and responded to antibiotics, the drug prescribed to treat seal finger.

Stories of so-called zombie diseases, or pathogens, like anthrax receive a lot of media attentionbut actual cases have, so far, been rare. Many scientists would say fears over ancient or historic diseases are overblown, and point to the fact that we are exposed to viruses on a near-constant basis.

"Viruses are everywherein soils, in ice, on money," Professor Paul Falkowski, who leads the Environmental Biophysics and Molecular Ecology Laboratory at Rutgers UniversityNew Brunswick, told Newsweek.

"Virtually all viruses have no effect on human health. However, some microbes, such as anthrax bacteria, can emerge from frozen soils after decades and infect people" He adds: "But the risk is very low."

When considering the possible health risk of ancient viruses, it is also important to think about exposure. Most infectious diseases are transmitted by direct contact, bodily fluids and respiratory droplets"in other words, there is virtually no danger of long range transmission," said Falkowski.

A virus found in an isolated region of Siberia or atop a Tibetan glacier might not be too risky because there is a low risk of exposure. In contrast, high concentrations of people in urban areas increases contact and exposure, which in turn increases the risk of disease outbreaks.

That may change as humans and animals respond to rising temperatures. Thawing of ice in the poles may affect how we navigate the planet, with new routes in the Arctic opening up. A changing climate may also push species to expand their range to new parts of the world. The current administration's plans to expand land available for drilling in the Arctic Circle, for example, could open up new paths to exposure.

Kreuder Johnson and her colleague Tracey Goldstein, Professor Pathology, Microbiology, Immunology at UC Davis told Newsweek these behavioral changes could lead to animals and microorganisms interacting in different ways or coming into contact with pathogens for the first time.

For example, Goldstein's research into the phocine distemper virus (PDV), a potentially deadly infectious disease that targets seals and other marine mammals.

The study found lower levels of sea ice in the Arctic circle were positively correlated with higher infection rates among certain seal species. The study's authors suggested changes in habitat and interactions between species may have been behind the spike.

Still, for now, the bulk of information we have is sparse and hypothetical. The potential for newor rather ancientmicrobes to re-emerge in a warming climate is a relatively new set of circumstances only starting to be researched.

"It's simply something we should keep on our radar," said Goldstein. "The climate is changing so quickly and we don't know what the next thing might be that's going to be a concern."

Claverie agrees: "Warming plus more people in previously uninhabited arctic regions are the recipe for disasterin theory," he said. "However, nobody knows how to estimate the probability of this to happen. We just know from our work with amoeba viruses that it is, in principle, a possibility."

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Melting Glaciers and Thawing Permafrost Could Release Ancient Viruses Locked Away for Thousands of Years - Newsweek