A "zombie" virus that was frozen in permafrost for 48,500 years has been awakened by scientists.

(CNN) ⸻ Warmer temperatures in the Arctic are thawing the region's permafrost, potentially stirring viruses that, after lying dormant for tens of thousands of years, could endanger animal and human health. Chemical and radioactive waste that dates back to the Cold War, which has the potential to harm wildlife and disrupt ecosystems, may also be released during thaws. To better understand the risks, Jean-Michel Claverie, an Emeritus professor of medicine and genomics at the Aix-Marseille University School of Medicine in Marseille, France, has tested earth samples taken from Siberian permafrost to see whether any viral particles contained therein are still infectious. Claverie studies a particular type of virus he first discovered in 2003, known as giant viruses, which are much bigger than the typical variety and visible under a regular light microscope, rather than a more powerful electron microscope. Permafrost is a good storage medium because it's an oxygen-free environment that light doesn't penetrate, but current day Arctic temperatures are warming up to four times faster than the rest of the planet, weakening the top layer of permafrost in the region. In 2014, Russian scientists revived a 30,000-year-old virus from the permafrost, making it infectious for the first time in 30,000 years. In 2015, Claverie and his team isolated a different virus type that also targeted amoebas, and in his latest research, published February 18 in the journal Viruses, isolated several strains of ancient virus from multiple samples of permafrost taken from seven different places across Siberia and showed they could each infect cultured amoeba cells. The oldest was almost 48,500 years old, based on radiocarbon dating of the soil, and came from a sample of earth taken from an underground lake 16 meters (52 feet) below the surface. The youngest samples, found in the stomach contents and coat of a woolly mammoth's remains, were 27,000 years old. Claverie fears people regard his research as a scientific curiosity and don't perceive the prospect of ancient viruses coming back to life as a serious public health threat. Traces of viruses and bacteria that can infect humans have been found preserved in permafrost. A lung sample from a woman's body exhumed in 1997 from permafrost in a village on the Seward Peninsula of Alaska contained genomic material from the influenza strain responsible for the 1918 pandemic. In 2012, scientists confirmed the 300-year-old mummified remains of a woman buried in Siberia contained the genetic signatures of the virus that causes smallpox. An anthrax outbreak in Siberia that affected dozens of humans and more than 2,000 reindeer between July and August in 2016 has also been linked to the deeper thawing of the permafrost during exceptionally hot summers. Birgitta Evengård, professor emerita at Umea University's Department of Clinical Microbiology in Sweden, said there should be better surveillance of the risk posed by potential pathogens in thawing permafrost, but warned against an alarmist approach. Scientists don't know how long these viruses could remain infectious once exposed to present-day conditions, or how likely the virus would be to encounter a suitable host. The risk is bound to increase in the context of global warming, as permafrost thawing will keep accelerating and more people will populate the Arctic in the wake of industrial ventures. Claverie isn't alone in warning that the region could become a fertile ground for a spillover event. Last year, a team of scientists published research on samples of soil and lake sediment taken from Lake Hazen, a freshwater lake in Canada. They sequenced the genetic material in the sediment to identify viral signatures and the genomes of potential hosts. They suggested the risk of viruses spilling over to new hosts was higher at locations close to where large amounts of glacial meltwater flowed into the lake. Identifying viruses and other hazards contained in the warming permafrost is the first step in understanding what risk they pose to the Arctic. Other challenges include quantifying where, when, how fast and how deep permafrost will thaw. Miner cataloged an array of potential hazards currently frozen in Arctic permafrost in a 2021 paper published in the scientific journal Nature Climate Change. These include buried waste from the mining of heavy metals and chemicals such as the pesticide DDT, which was banned in the early 2000s. Radioactive material has been dumped in the Arctic since the 1950s, and rapid thaw exposes old permafrost horizons, releasing compounds and microorganisms sequestered in deeper layers. Miner labeled the direct infection of humans with ancient pathogens as "currently improbable". However, she is worried about what she termed "Methuselah microorganisms" (named after the Biblical figure with the longest life span). These organisms could bring the dynamics of ancient and extinct ecosystems into the present-day Arctic, with unknown consequences. The re-emergence of ancient microorganisms has the potential to change soil composition and vegetative growth, possibly further accelerating the effects of climate change. The best course of action is to halt the thaw, and the wider climate crisis, and keep these hazards entombed in the permafrost for good.