Pathogenic microorganisms in frozen environments

As of 2023, there has been at least one recorded reemergence of anthrax, a pathogen long-known for its ability to hibernate in soils. There have also been several cases when truly novel microorganisms discovered in the frozen environments were successfully revived by researchers, or were found live in a recently thawed environment. So far, most only affect amoebas, and none have been known to pose a risk to humans or to crops. Of the already-studied pathogens, at least one anthrax outbreak has been connected to decades-old infected carrion thaw; yet, samples of influenza and smallpox pathogens have failed to survive the thaw even in laboratory conditions. Some researchers have also raised alarm about the potential of horizontal gene transfer between ancient and modern bacteria, and the risk it could exacerbate the challenge of antibiotic resistance. At the same time, other scientists consider these concerns overblown, and argue that ancient microorganisms are unlikely to make a difference today.

Timeline of research into the subject

20th century

Johan Hultin made multiple attempts during the 20th century to culture 1918 influenza virus he found in the frozen corpses of pandemic victims at Brevig Mission in Alaska. Every attempt failed, which suggested that the influenza virus is incapable of surviving the thaw after being frozen. In the 1990s, other scientists have tried to revive pneumonia-causing bacteria and the smallpox virus, yet all of those attempts were unsuccessful as well.

1999

A group of researchers was able to extract potentially viable microscopic fungi, as well as the RNA of tomato mosaic virus, from Greenland ice cores up to 140,000 years old.

2004

It was estimated that between 10¹⁷ and 10²¹ microorganisms, ranging from fungi and bacteria in addition to viruses, were already released every year due to ice melt, often directly into the ocean. According to researchers behind this estimate, only viruses with high abundance, ability to be transported through ice, and ability to resume disease cycles after the thaw would be of any concern.

In particular, caliciviruses of Vesivirus genus were hypothesized as the most likely to spread from ancient ice, due to their high abundance and using ocean animals as hosts, where the migratory nature of many species of fish and birds could potentially enable a high transmission rate. Caliciviruses are poorly adapted to humans, and the only known infections were of marine biologists who worked closely with infected seals. However, Enteroviruses (a group which includes polioviruses, echoviruses and Coxsackie viruses) and even influenza A were also considered less likely but still plausible candidates.

2005

In the 1960s, the United States Army Corps of Engineers had dug out Fox tunnel in Alaska, to provide a good test ground to better understand permafrost before the construction of the Trans-Alaska Pipeline System. By 2005, scientists revisiting that tunnel have discovered frozen cells of carnobacterium pleistocenium, with an estimated age of 32,000 years. Melting the ice had revived them, resulting in the first documented case of an organism "coming back to life" from ancient ice. None of the bacteria in carnobacterium genus are known to be pathogenic in humans, although some are known for spoiling chilled food products, and one species may cause disease in fish.

2011

A paper by two Russian scientists in Global Health Action, a journal published by Umeå University in Sweden, had warned of the risk that the old burial grounds of cattle which had died to anthrax in the early last century may thaw and lead to the re-emergence of the viable pathogen. The authors noted that at the time, there were about 13,885 cattle burial grounds in Northern Russia, a substantial fraction of which did not meet sanitary standards, and some had their maps or other records missing.

2014

A completely unknown plant virus was revived from a frozen caribou feces deposit which was only 700 years old. It was named "ancient caribou feces associated virus" (aCFV) by its discoverers. The scientists have also introduced this virus into the tissues of Nicotiana benthamiana, a common model species for plant pathogens. aCFV had successfully replicated, yet was unable to cause more than an asymptomatic infection. According to the researchers, this either suggests a large genetic distance between the original host species of aCFV and more modern plants, or that N. benthamiana was simply a suboptimal host for this species.

Also in 2014, two ~30,000 years old giant virus species, Pithovirus sibericum and Mollivirus sibericum, were discovered in the Siberian permafrost and they retained their infectivity. Like the other giant viruses with large genomes, they are larger in size than most bacteria and pose no risk to humans, as they infect other microorganisms like Acanthamoeba, a genus of amoebas.

2016

An anthrax outbreak had occurred in the Yamal Peninsula region in Northern Russia. It was thought to be linked to an infected reindeer corpse, which died 75 years earlier, yet had thawed after a heatwave. Over 2,000 reindeer had been infected and the disease had spread to humans, hospitalizing dozens and killing a child before the outbreak was contained.

2023

The same team of French researchers behind the 2014 revival of two giant viruses had also managed to revive 8 more ancient amoeba-infecting viral species. Four of these species were from the pandoravirus, cedratvirus (sometimes classified as a subgroup of pithovirus), megavirus and pacmanvirus (part of Asfarviridae) families, which weren't previously revived from the permafrost. In addition, five more species from these families were found in already thawed permafrost, with no way to tell their age. The oldest revived virus was a 48,500-year-old Pandoravirus yedoma.