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Scientists have revived a ‘zombie’ virus that spent 48,500 years frozen in permafrost
Warmer temperatures in the Arctic are thawing the region’s permafrost — a frozen layer of soil beneath the ground — and potentially stirring viruses that, after lying dormant for tens of thousands of years, could endanger animal and human health.
While a pandemic unleashed by a disease from the distant past sounds like the plot of a sci-fi movie, scientists warn that the risks, though low, are underappreciated. 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.
“There’s a lot going on with the permafrost that is of concern, and (it) really shows why it’s super important that we keep as much of the permafrost frozen as possible,” said Kimberley Miner, a climate scientist at the NASA Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, California.
Permafrost covers a fifth of the Northern Hemisphere, having underpinned the Arctic tundra and boreal forests of Alaska, Canada and Russia for millennia. It serves as a kind of time capsule, preserving — in addition to ancient viruses — the mummified remains of a number of extinct animals that scientist have been able to unearth and study in recent years, including two cave lion cubs and a woolly rhino.
The reason permafrost is a good storage medium isn’t just because it’s cold; 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.
To better understand the risks posed by frozen viruses, 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. He’s in search of what he describes as “zombie viruses” — and he has found some.
The virus hunter
Claverie studies a particular type of virus he first discovered in 2003. Known as giant viruses, they are much bigger than the typical variety and visible under a regular light microscope, rather than a more powerful electron microscope — which makes them a good model for this type of lab work.
His efforts to detect viruses frozen in permafrost were partly inspired by a team of Russian scientists who in 2012 revived a wildflower from a 30,000-year-old seed tissue found in a squirrel’s burrow. (Since then, scientists have also successfully brought ancient microscopic animals back to life.)
In 2014, he managed to revive a virus he and his team isolated from the permafrost, making it infectious for the first time in 30,000 years by inserting it into cultured cells. For safety, he’d chosen to study a virus that could only target single-celled amoebas, not animals or humans.
He repeated the feat in 2015, isolating a different virus type that also targeted amoebas. And in his latest research, published February 18 in the journal Viruses, Claverie and his team 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.
Those latest strains represent five new families of viruses, on top of the two he had revived previously. 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.
That amoeba-infecting viruses are still infectious after so long is indicative of a potentially bigger problem, Claverie said. He 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.
“We view these amoeba-infecting viruses as surrogates for all other possible viruses that might be in the permafrost,” Claverie told CNN.
“We see the traces of many, many, many other viruses,” he added. “So we know they are there. We don’t know for sure that they are still alive. But our reasoning is that if the amoeba viruses are still alive, there is no reason why the other viruses will not be still alive, and capable of infecting their own hosts.”
Precedent for human infection
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, allowing old spores of Bacillus anthracis to resurface from old burial grounds or animal carcasses.
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.
“You must remember our immune defense has been developed in close contact with microbiological surroundings,” said Evengård, who is part of the CLINF Nordic Centre of Excellence, a group that investigates the effects of climate change on the prevalence of infectious diseases in humans and animals in northern regions.
“If there is a virus hidden in the permafrost that we have not been in contact with for thousands of years, it might be that our immune defense is not sufficient,” she said. “It is correct to have respect for the situation and be proactive and not just reactive. And the way to fight fear is to have knowledge.”
Chances of viral spillover
Of course, in the real world, 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. Not all viruses are pathogens that can cause disease; some are benign or even beneficial to their hosts. And while it is home to 3.6 million people, the Arctic is still a sparsely populated place, making the risk of human exposure to ancient viruses very low.
Still, “the risk is bound to increase in the context of global warming,” Claverie said, “in which permafrost thawing will keep accelerating, and more people will populate the Arctic in the wake of industrial ventures.”
And Claverie isn’t alone in warning that the region could become a fertile ground for a spillover event — when a virus jumps into a new host and starts to spread.
Last year, a team of scientists published research on samples of soil and lake sediment taken from Lake Hazen, a freshwater lake in Canada located within the Arctic circle. They sequenced the genetic material in the sediment to identify viral signatures and the genomes of potential hosts — plants and animals — in the area.
Using a computer model analysis, 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 — a scenario that becomes more likely as the climate warms.
Unknown consequences
Identifying viruses and other hazards contained in the warming permafrost is the first step in understanding what risk they pose to the Arctic, Miner at NASA’s Jet Propulsion Laboratory said. Other challenges include quantifying where, when, how fast and how deep permafrost will thaw.
Thawing can be a gradual process of as little as centimeters per decade, but also happens more rapidly, such as in the case of massive land slumps that can suddenly expose deep and ancient layers of permafrost. The process also releases methane and carbon dioxide into the atmosphere — an overlooked and underestimated driver of climate change.
Miner cataloged an array of potential hazards currently frozen in Arctic permafrost in a 2021 paper published in the scientific journal Nature Climate Change.
Those possible dangers included 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 also been dumped in the Arctic — by Russia and the United States — since the advent of nuclear testing in the 1950s.
“Abrupt thaw rapidly exposes old permafrost horizons, releasing compounds and microorganisms sequestered in deeper layers,” Miner and other researchers noted in the 2021 paper.
In the research paper, Miner labeled the direct infection of humans with ancient pathogens released from permafrost as “currently improbable.”
However, Miner said she is worried about what she termed “Methuselah microorganisms
” (named after the Biblical figure with the longest life span). These are organisms that 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, Miner said.
“We’re really unclear as to how these microbes are going to interact with the modern environment,” she said. “It’s not really an experiment that I think any of us want to run.”
The best course of action, Miner said, is to try and halt the thaw, and the wider climate crisis, and keep these hazards entombed in the permafrost for good.
注释：
permafrost: n
表示"永久冻土层"，means "ground that is permanently frozen"，如：Melting permafrost will hit existing and planned infrastructure.冻土融化将冲击我们现有的和计划中的基础设施建设。
dormant: adj
表示"休眠的"，means "n a condition of biological rest or suspended animation"，如：Many living things are dormant in winter.很多生物到了冬季都休眠。
unleash: v
表示"释放"，means " set (feelings,forces,etc.) free from control and allow them to act with full force"，如：Go at once,or I will unleash my dog on you!立刻走，要不我就放我的狗咬你！
underappreciated: adj
表示"未得到正确评价的,未受到充分赏识(或欣赏)的."，means "less appreciated"，如：Poets are typically poor and underappreciated. 诗人是典型的穷人和不被欣赏的人。
Propulsion: n
表示"推进"，means "the act of propelling"，如：This aircraft works by jet propulsion.这架飞机是喷气推进的。
underpin: v
表示"支撑"，means "support from beneat"，如：China needs regional stability to underpin its continued economic growth. 中国需要地区稳定来巩固其持续的经济增长
tundra: n
表示"苔原"，means "a vast treeless plain in the Arctic regions where the subsoil is permanently frozen"，如：In the north are vast stretches of icy, treeless tundra.北部为冰天雪地的没有树木的辽阔平原，称之为冻原带。
boreal: adj
表示" 北(方)的；北风的"，means "comprising or throughout far northern region"，如：Boreal forest is located primarily in Canada, Russia, and Alaska.北方森林主要分布在加拿大、俄国和阿拉斯加。
woolly: adj
表示"毛茸茸的"，means "having a fluffy character or appearance"，如：I like the feel of this cloth; it has a warm woolly feel.我喜欢这块布给我的感觉，它摸上去毛茸茸的很暖和。
pose: v
表示" 摆姿势"，means "assume a posture as for artistic purpose"，如：Please sit still while you pose for your photo.你摆好姿势拍照时请坐着别动。
Emeritus: adj
表示" 名誉退休的"，如：Perhaps I can introduce Mr. Lake Kirby, an emeritus professor from Washington University.请允许我介绍华盛顿大学名誉教授莱克柯尔比先生
genomics: n
表示" [复](用作单)基因组学"，如：Comparative genomics is one important part of human genome plan. 比较基因组学是人类基因组计划的重要组成部分。
revive: v
表示" 复生"，means "bring back to consciousness, strength, health or an earlier state"，如：We tried to revive him but without avail. 我们试图使他苏醒,但没有成功。
burrow: v
表示"挖洞"，means " make sth by digging"，如：You burrow and rankle in his heart! 你挖掘并折磨他的心灵！
amoeba: n
表示" 阿米巴；变形虫"，如：Now we will create an algae and amoeba in the ocean that will do the same. 现在，我们将会在海洋中产生出一种海藻还有一种阿米巴变形虫，来做同样的事情。
radiocarbon: n
表示" 放射性炭"，如：The material in this beach has been dated by radiocarbon. 这个海滩上的物质经过放射性碳测定。
mammoth: n
表示"猛犸",如：The woolly mammoth was a month old when she died. 这只长毛象刚满月就不幸身亡。
surrogate: n
表示" 代理人"，means "a person appointed to represent or act on behalf of others"，如：I do not know if your company has surrogate in our country.我不知道贵公司在我国是否有代理。
exhume: v
表示"发掘"，means "dig up for reburial or for medical investigation;"，如：When the police exhumed the corpse they discovered traces of poison in it.警方掘出尸体，发现有中毒的痕迹
influenza: n
表示" 流行性感冒"，means "an acute febrile highly contagious viral disease"，如：The girl has come down with influenza.这女孩得了流行性感冒。
anthrax: n
表示" 炭疽病"，means "a highly infectious animal disease (especially cattle and sheep); it can be transmitted to people"，如：It is not a good idea to culture anthrax in your home.在家中培育炭疽病毒可不是好玩的。
spore: n
表示"孢子"，如：Mushroom's spores are usually carried on the wind. 蘑菇的孢子通常由风传播。
Bacillus：n
表示" 杆状菌；细菌"，means "aerobic rod-shaped spore-producing bacterium"，如：We can not see bacillus with eyes.我们不能用肉眼看到杆状菌。
Bacillus anthracis: 表示"炭疽杆菌,炭疽芽孢杆菌"
carcass: n
表示" 尸体；"，means " dead body of an animal"，如：Vultures are picking at a lion's carcass.秃鹫正在啄食狮子的尸体。
pathogen: n
表示"病原体"，means "any disease-producing agent (especially a virus or bacterium or other microorganism)"，如：The opposite end latches onto the pathogen.相对的一端锁在病原体上。
prevalence: n
表示"流行"，means "the quality of prevailing generally; being widespread"，如：Thus, lists of STDs may change over time and include more or fewer diseases depending on their prevalence.所以，性传播疾病的病名录可以随时发生改变，以及依据其流行程度会作出调整
benign: adj
表示"良性的"，means "(of a disease) not dangerous to life;not malignant"，如：After tests the tumor was found to be benign. 检测发现肿瘤是良性的。
sediment: n
表示" 沉淀物"，means " solid material that settles to the bottom of a liquid"，如：He emptied out the water barrel to clear it of sediment. 他把水桶倒空以清掉桶底的沉淀物。
slump: n
表示"暴跌；"，means "a noticeable deterioration in performance or quality;"，如：The slump hit his business hard. 物价暴跌使他的生意大受打击。
methane: n
表示"沼气"，means "a colorless odorless gas used as a fuel"，如：Cattle release methane when they digest their food. 牛在消化食物时,会释放出甲烷。
advent: n
表示"出现"，means " the coming of an important event"，如：The advent of the computer changed people's life greatly. 计算机的出现极大地改变了人们的生活。
Methuselah: n
表示"非常高寿的人"，means "a man who is very old"，如：I wish you bounty happiness and longevity of Methuselah. （我祝您福如东海，寿比南山。）
microorganism: n
表示"微生物"，means "any organism of microscopic size"，如：Bacteria belong to the microorganism. 细菌属于微生物。
vegetative: adj
表示"植物生长的"，means "composed of vegetation or plants"，如：They are not an issue and they are surely not vegetative matter. 他们不是问题，他们确实不是植物的问题
entomb: v
表示" 埋葬；"，means "place in a grave or tomb;"，如：Workers are still trying to entomb the reactor in concrete. 工人们仍然正在设法用混凝土把反应堆埋起来。
中文简要说明：
美国有线电视新闻网（CNN）报导，覆盖北半球1／5面积的永冻土，千年来遍布北极、阿拉斯加、加拿大、俄罗斯地区，它们宛如时空胶囊，封存古代病毒、已经成为木乃伊的灭绝动物遗骸，不过随着全球暖化、气温上升，永冻土的表层逐渐融化，科学家担心这些重新出土的病毒可能危及动物及人类健康。
法国艾克斯马赛大学（Aix Marseille University）医学院荣誉退休教授克拉维里，数年来持续研究从永冻土采检回来的病毒，以研究这些病毒是否还活着，他形容这些病毒是「殭尸病毒」。
2014年他与团队将一株3万年前的病毒植入一个培养细胞，首度让冰冻的病毒「复活」，为了安全起见，他们选择研究只能感染单细胞生物阿米巴原虫的病毒。
2015年，克拉维里团队又分离出另一株攻击阿米巴原虫的病毒；紧接着今年2月18日，团队在期刊《Viruses》发表最新研究，指出他们从西伯利亚永冻土各地取回的样本中，分离出多株古代病毒，而且这些病毒都能感染阿米巴原虫细胞。
其中最老的一株病毒可追溯至4万8500年前，这株病毒是从永冻土下16公尺深的地下湖中发现，当中最年轻的病毒可回溯至2万7000年前，是在一头长毛象遗骸的毛皮及胃中发现。
克拉维里指出，这些感染阿米巴原虫的病毒在这么久之后仍具传染力，显示可能存在更大问题。他说团队在西伯利亚永冻土发现了许多其他病毒的踪迹，「我们知道它们就在那里，我们不是很确定它们是否还活着，但我们的推论是，如果阿米巴原虫病毒还活着，其他病毒就有可能还活着，而且有能力感染宿主。」
■永冻土曾发现人传人病毒
过去确实有研究团队在冻土层发现了能感染人类的病毒或细菌。例如，1997年科学家在阿拉斯加永冻土掘出的女尸身上，发现引发1918年西班牙流感疫情的病毒株。2012年，科学家证实在冰冻300年的西伯利亚女木乃伊身上发现天花病毒的遗传标记。
■殭尸病毒会扩散？
瑞典乌米亚大学（Umea University）临床微生物学系荣誉退休教授艾文佳德（Birgitta Evengård）表示，确实应该更好地监控永冻土融化后可能构成的病原体威胁，但她强调没有必要恐慌。
CNN指出，科学家至今仍不清楚，这些殭尸病毒暴露在现在的环境下能存活多久，以及有没有机会遇到合适的宿主。另外，北极地区人烟稀少，人类接触这些古老病毒的风险也跟着降低。
不过克拉维里认为，全球暖化的脉络下，风险势必上升，随着永冻土消融，会有愈来愈多人移居北极。
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