As permafrost melts as a result of climate change, ice that has been frozen for thousands of years may begin to release viruses and bacteria that human immune systems may be unprepared for.

In August of last year, a 12 year old boy died after being infected with anthrax in the Yamal peninsula of Siberia. Scientists have theorized that a reindeer died from the disease over 75 years ago, and its carcass was trapped under the frozen soil known as permafrost. The soil thawed during a heatwave that month, releasing infectious anthrax into the water, soil, and finally the food supply, when 2,000 reindeer were infected nearby. This led to a small number of human cases.

In normal conditions, the top layers of permafrost, about 50 cm deep, thaw each summer. But as temperatures rise as a result of global warming, older layers of permafrost have begun to melt. Bacteria can survive in frozen permafrost soil for very long periods of time, potentially for millions of years. Temperatures in the Arctic circle are rising about 3 times faster than temperatures in the rest of the world. It is possible more bacteria or viruses could be released as more permafrost melts.

According to evolutionary biologist Jean-Michel Claverie, of Aix-Marseille University in France:

“Permafrost is a very good preserver of microbes and viruses, because it is cold, there is no oxygen, and it is dark. Pathogenic viruses that can infect humans or animals might be preserved in old permafrost layers, including some that have caused global epidemics in the past.”

A 2014 study, led by Claverie, revived two viruses that had been preserved in Siberian permafrost for 30,000 years. They were discovered under 100 feet of permafrost in coast tundra. Once revived, these viruses, which only affect single-celled amoebas, quickly became infectious again.

Moreover, global warming exposes this permafrost to other dangers besides melting. As Siberia’s north shore becomes more accessible by sea, it becomes possible that drilling or mining, once out of the question in the frozen landscape, could unearth infectious agents in the ice.

“At the moment, these regions are deserted and the deep permafrost layers are left alone. However, these ancient layers could be exposed by the digging involved in mining and drilling operations. If viable virions are still there, this could spell disaster,” said Claverie.

Addressing the possibility of these microbes being a danger to humans, Claverie explains:

“How likely that is is not known, but it’s a possibility. It could be bacteria that are curable with antibiotics, or resistant bacteria, or a virus. If the pathogen hasn’t been in contact with humans for a long time, then our immune system would not be prepared. So yes, that could be dangerous.”

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