Zombie virus: Can a 50,000-year-old pathogen plague us today?

Climate change and global warming have accelerated the thawing of the frozen soils in the Siberian Arctic, called permafrost. It could unleash microbes lying dormant for millions of years in the frozen earth. Many of these viruses could pose a threat to humans and wildlife.

That sounds more like science fiction. A pandemic from the past is an unlikely alarming scenario; still, a virus from a bygone era cannot be ruled out. More so since researchers have resurrected several viruses from permafrost dating back more than 48,500 years, proving that prehistorical viruses can remain infectious.

The risk is real but low. That is because scientists don’t know whether these viruses could remain infectious in present-day conditions. Moreover, the sparse population in the Arctic reduces the risk of human exposure to ancient viruses.

Kimberley Miner, climate scientist at the Nasa Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, told CNN: “It’s super important that we keep as much of the permafrost frozen as possible”. That means humankind has to try and slow global warming. That requires climate action.

Let’s look at how real the threat is.

What’s permafrost?

It’s the permanently frozen (0°C or colder) layer of soil lying beneath the ground for more than two years. It has a rich mixture of decaying organic matter with a vast and diverse population of microorganisms.

Around 15 per cent of the Northern Hemisphere (including the Arctic, Alaska, Canada and Russia) or 11 per cent of the global surface, is covered by permafrost. Some permafrost could be millions of years old.

Why’s permafrost a good storage medium?

Permafrost is a cold environment devoid of oxygen and light. Below the active layer, the absence of water stops all metabolic activities, killing most microbes. But, some can go into an inactive state called “cryptobiosis”, which allows them to come alive in the right conditions, French researcher Jean-Michel Claverie wrote on the Think Global Health website. “Permafrost offers ideal conditions for the preservation of cellular structures as well as DNA. It is cold, dark, anoxic, and neutral, all the opposite of what rapidly destroys microbes at the surface: heat, UV light, oxygen, and extreme pH.”

What’s a zombie virus?

Claverie is a zombie virus hunter. According to him, zombie viruses are microbes in permafrost that can still be infectious. The Emeritus professor of medicine and genomics at the Aix-Marseille University School of Medicine in Marseille believes ancient and unknown viruses are a public health threat since Arctic temperatures are warming up to four times faster than the rest of the planet, thawing permafrost.

Which are the viruses revived from permafrost?

Claverie, inspired by Russian scientists who in 2012 revived a wildflower from a 30,000-year-old seed tissue, attempted to resurrect viruses that target only amoebas. In 2014, the French researcher and his team made a virus from the permafrost infectious for the first time in 30,000 years. In the following year, he isolated another virus. In his latest research, published in the journal Viruses, Claverie said his team removed several strains of virus from permafrost taken from seven different places in Siberia and showed they could each infect cultured amoeba cells, a CNN report said.

What’s the oldest virus revived by French researchers?

Claverie and his team revived a virus that spent 48,500 years frozen in permafrost. It was collected from an earth sample at the bottom of an underground lake. One of the strains revived included a 27,000-year-old sample taken from the stomach of a woolly mammoth.

Can microbes in permafrost infect humans?

Traces of pathogens have been found preserved in permafrost. The influenza strain responsible for the 1918 pandemic was found by pathologist Johan Hultin in a woman’s lung tissue preserved in permafrost in Brevig Mission village on Alaska’s Seward Peninsula, according to a report on the University of Alaska Fairbanks website.

In 2012, French and Russian researchers found smallpox DNA in 300-year-old mummies from Siberia, a New England Journal of Medicine report said.

Thawing permafrost in the Yamal Peninsula in Russia was linked to a massive anthrax outbreak that affected dozens of humans and more than 2,000 reindeer in 2016, according to an NPR report.

How long will viruses from permafrost remain infectious?

It’s impossible to estimate the infectiousness of a virus recovered from permafrost after it is exposed to outdoor conditions (UV light, oxygen, heat), Claverie wrote on the Think Global Health website. “But it is already clear that the risk associated to the ‘zombie viruses’ scenario” is bound to increase in the context of global warming as permafrost thawing keeps accelerating,” he added.

How will our immune system handle zombie viruses?

The immune systems of humans may not be adept at handling pathogens from the past, Birgitta Evengard, professor emerita at Umea University’s Department of Clinical Microbiology in Sweden, told CNN, calling for better surveillance of the risk posed by pathogens in thawing permafrost.

“You must remember our immune defence has been developed in close contact with microbiological surroundings,” Evengard said. “If there is a virus hidden in the permafrost that we have not been in contact with for thousands of years, it might be that our immune defence is not sufficient,” she added.

Can modern antibiotics control ancient bacteria?

French researcher Claverie believes an epidemic caused by an ancient bacterium could be controlled by modern antibiotics, although antibiotic-resistant genes have been found in permafrost. “Antibiotics target cellular structures or block metabolic pathways that have been conserved in all bacteria since a billion years of evolution. By design, these drugs are broad-spectrum antibiotics,” he wrote.

What about the threat from viruses?

Antibiotics target bacteria, not viruses. And viruses do not share universally conserved metabolic processes. So there cannot be a “broad-spectrum” solution to viruses. “It is therefore legitimate to focus on the risk posed by viral particles released from the thawing of thousands of years of permafrost layers,” Claverie wrote on the Think Global Health website.

How real is the threat of a virus from the past?

The risk of an unknown virus that sickened Neanderthals returning to infect us Homo sapiens is unlikely, but it has become a real possibility with the thawing permafrost.

“The risk is bound to increase in the context of global warming, in which permafrost thawing will keep accelerating, and more people will populate the Arctic in the wake of industrial ventures,” Claverie warned.

So the best option is to prevent a climate crisis. That will keep the pathogens buried in the permafrost.