As a changing climate continues to warm the planet and thaws ancient permafrost, some people are concerned that long-dormant pathogens, or “zombie viruses,” could emerge from the newly thawed ground, unleashing new epidemics or pandemics on the world.

While these concerns provide good fodder for a science fiction thriller, California State University, Northridge biology professor Rachel Mackelprang wanted to assure members of the public that they shouldn’t be overly concerned.

“The idea that ancient preserved viruses could emerge when permafrost thaws sounds plausible,” said Mackelprang, who teaches in CSUN’s College of Science and Mathematics. “There are many reasons why we should be concerned about climate change and thawing permafrost, but the release of pathogenic viruses is not one of them.”

Mackelprang and her colleagues — Robyn A Barbato with the U.S. Army Cold Regions Research and Engineering Laboratory, Andrew M Ramey with the U.S. Geological Survey Alaska Science Center, Ursel M. E. Schütte with the Institute of Arctic Biology at the University of Alaska Fairbanks and Mark P. Waldrop with the U.S. Geological Survey, Geology, Minerals, Energy, and Geophysics Science Center — spent months reviewing research from a diverse range of disciplines to determine whether ancient viruses released by thawing permafrost posed a threat.

They examined efforts to recover infectious viruses from human remains, studies on disease occurrence in polar animal populations, investigations into viral persistence and infectivity in permafrost and assessments of human exposure to enormous viral diversity present in the environment.

They found that “evidence shows that human pathogenic viruses, such as those causing smallpox and the 1918 influenza pandemic, do not survive in permafrost. Viruses able to persist in permafrost infect cold-tolerant microorganisms such as amoeba and bacteria, but can’t infect humans. We concluded that the risk posed by viruses from thawing permafrost is no greater than that from viruses found other environments, such as temperate soils and aquatic systems,” Mackelprang said.

Their findings, “Cooling perspectives on the risk of pathogenic viruses from thawing permafrost,” were published last year in mSystems, a journal of the American Society for Microbiology.

Mackelprang said she can appreciate the public’s fascination with the idea of “zombie viruses.”

“The idea that ancient viruses could be resurrected from permafrost and initiate pandemics is startling. It can be a little bit terrifying. And, like doom scrolling, it can be fascinating,” she said. “But they pose no more a threat than environmental viruses we encounter in day to day lives.”

Mackelprang pointed out that human beings can be exposed to an enormous number of viruses every day from environments such as soil, sea water, indoor surfaces, and the air we breathe.

“We live in a microbial world filled with bacteria and the viruses that infect them. For example, a single gram of soil can contain more than a billion viruses. We are constantly exposed to these viruses, but they don’t infect humans.

Scientists have tried to revive ancient viruses — including the 1918 influenza virus that infected nearly a third of the world’s population at the time and killed of millions of people and the now eradicated deadly smallpox — from permafrost remains.

“Small degraded fragments of viral DNA and RNA have been recovered from smallpox and influenza victims buried in permafrost. These shattered remnants, however, are not infectious. This finding is particularly notable for the smallpox virus, which is known for its ability to survive outside the human body. Not even the virus causing smallpox could be revived from permafrost remains.”

Viruses that could jump from ancient animal remains, such as mammoths, to humans also do not survive in permafrost, she said.

“Most animal remains preserved in permafrost are thousands of years old, versus decades to hundreds of years for influenza and smallpox victims” Mackelprang said. “The likelihood that viruses would survive that time scale when they don’t survive for a few hundred years is very low.”

The third, theoretical risk posed by permafrost viruses would be from microbial hosts that would transfer a virus to animal or human populations. But there is very little precedent of that happening, Mackelprang said.

“The lack of precedent for microbial viruses jumping to human or animal hosts suggests this scenario is unlikely to arise from thawing permafrost,” she said.

While the idea of permafrost viruses could unleash an epidemic or new pandemic on the world can be titillating, Mackelprang said “it is not particularly useful and perhaps even harmful.”

“Stoking fears of viruses in thawing permafrost may inadvertently discourage customary and traditional cultural practices among subarctic and Arctic residents or divert attention from the more pressing ways that pathogens in the warming Arctic pose a risk to human health and well-being,” she said. “For example, wildlife and humans increasingly occupy shared habitats, providing opportunities for viruses maintained in animals to spill over into humans.

“Arthropod and rodent disease vector ranges are expanding and shifting northward,” Mackelprang continued. “Extreme precipitation and flooding events are increasing, threatening infrastructure such as water and waste treatment facilities. Higher temperatures increase the survival of some water-borne disease agents. Furthermore, wildlife health maybe affected as a consequence of climate change, which further compromises fragile ecosystems and the people that rely on them.

“We have a lot of things we should be worrying about,” she said. “But ‘zombie viruses’ emerging from thawing permafrost is not high on the list.”