As permafrost thaws, could ‘zombie pathogens’ make a comeback?

Photo courtesy the U.S. National Parks Service

Undead beings from an ancient era, frozen in time and released upon a modern society that has forgotten them — sounds like a horror movie premise, right?

Scientists have been discussing whether this scenario will become reality, but don’t worry about fighting off a hoard of zombies anytime soon. We’re talking about bacteria and viruses that have remained frozen for centuries in the permafrost of the earth’s coldest regions. Today, as global temperatures rise, and permafrost begins to thaw more frequently and for longer periods of time, scientists are talking about the possibility of these pathogens making a reappearance.

To see if such a thing would be possible, a pair of microbiologists warmed up a sample of Russian permafrost suspected to contain viruses. The researchers added an amoeba to the sample, and watched as a 30,000-year-old virus, Pithovirus sibericum, showed up to attack the virus-bait.

This virus, along with most others found in permafrost, is harmless to humans (but not amoebae). Researchers aren’t sure if anything more dangerous could reappear as temperatures warm. There are reportedly tens of thousands of bodies left in permafrost regions of the world, and the likelihood that some may contain old illnesses, like smallpox, is high.

An old bacteria could have resurfaced in 2016 when a heat wave hit the Arctic wilderness of Siberia. The warmth caused frozen, decades-old reindeer carcasses to thaw. These reindeer had died of anthrax poisoning, a bacterial disease. Meanwhile, a massive anthrax outbreak affected nearby reindeer herders and their animals. Families were evacuated, and troops trained for biological warfare were sent in to help. One young boy and over 2,300 reindeer died in the outbreak.

It’s possible that it was a coincidence that the anthrax outbreak coincided with the heatwave, some argue, pointing out that anthrax can hibernate and return at certain points, regardless of temperature.

One case may be telling, though. In 2017, a teacher named Zac Peterson was working on an archaeological dig in Alaska when he came down with a strange skin infection. A large, painful red spot grew on the front of his leg, which doctors found to be seal finger infection, which hunters commonly get from handling contaminated seals. However, the only seals Peterson had been near were seals preserved in the permafrost of the 800-year-old cabin he had been excavating.

Is it conclusive? Not quite, but Peterson and others believe it’s quite possible the preserved seals passed on latent bacteria.

“Even if there’s a possibility it was something else,” Peterson told NPR, “I still tell people that I got infected by an 800-year-old strain of a seal hunter’s disease that was trapped in ice.”

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