A team of French, German and Russian scientists has recently succeeded in reviving giant viruses that had been buried in the frozen ground of Siberia for tens of thousands of years.
Thirteen of these viruses (of the genera Pandoravirus, Megavirus, Pacmanvirus, etc.) taken from samples of Siberian permafrost (permafrost in French), could be “reanimated”. The "youngest" of these Lazarus was 27 years old. And the oldest – a Pandoravirus – approached 48 years ago. It is, for the time being, the oldest virus to have been resuscitated.
Results that raise questions, as the planet – and the Far North – is warming… This is what motivated this study, which complements previous work and fills a gap in the available data.
Thawing permafrost releases organic matter that has been frozen for millennia, including bacteria and viruses, some of which can still reproduce. Now, while reports describing the bacteria found in these frozen areas abound, they are much more limited on viruses. This incorrectly suggests that such so-called "zombie" viruses are rare and do not pose a threat to public health.
The study on these thirteen ghosts is a "Preprint", so its results have yet to be examined by other scientists. But as the authors point out, it is already “legitimate to wonder about the risk that old viral particles will remain infectious and be put back into circulation by the thawing of old layers of permafrost”.
Indeed, what do we really know to date of the risks posed by these zombie viruses?
window to the past
Assuming that the samples collected were not contaminated during their extraction, the giant viruses recovered literally come from the past: more precisely from several tens of thousands of years ago. And we're talking about several different kinds of these particular organisms.
Moreover, this is not the first time that a viable virus has been detected in permafrost samples. The studies that paved the way for this work date back to 2014, when detected for the first time Pithovirus, then a Mollivirus one year later. The possibility of such resurrections is therefore real… With what consequences for fauna and flora – and us?
All the viruses found so far in such samples are giant DNA viruses, which only affect (in the current state of knowledge) amoebae (unicellular organisms). They are therefore very different from “classic” viruses (with a much smaller genome), which affect mammals for example, and it is very unlikely that they represent a danger for human beings.
If one of these giant amoeba-infecting viruses, called Acanthamoeba polyphaga mimivirusWas associated with pneumonia in humans, the causal relationship between the two is not established. Viruses cultured from permafrost samples therefore do not appear to pose a threat to public health themselves. But they are not the only ones to populate these frozen soils since prehistoric times: there are also entities that we know are dangerous for our species.
Of concern is that thawing permafrost could free the bodies of people who have been dead for decades if not centuries from an infectious disease. which could give the causative pathogens the opportunity to return. And epidemics are not lacking in history…
Those that worry scientists the most are, paradoxically, linked to the only human disease to have been eradicated worldwide, thanks to vaccination: smallpox. Its reintroduction, especially in hard-to-reach areas, could lead to a global health catastrophe. However, 300-year-old evidence of smallpox infection has been detected in bodies buried in Siberia...
Fortunately, these are only "partial genetic sequences", that is to say fragments of the virus's DNA too damaged to still be able to infect someone. However, the smallpox virus survives well when frozen in good conditions at -20°C, but only for a few decades – not centuries.
The Spanish flu also raised its share of questions. Over the past two decades, scientists have indeed exhumed the bodies of people who were swept away by this pandemic a century ago and buried in Alaskan permafrost and Svalbard, Norway. Its genome could be read (sequenced), but the influenza virus itself could not be "grown" (resurrected) in the laboratory from the tissues of the deceased. Flu viruses can survive in the freezer for at least a year, but probably not several decades.
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Bacteria could be more of a problem
While viruses do not seem to be a major threat at present, other types of pathogens, such as bacteria, could however pose more problems.
Over the years, several unexpected outbreaks of anthrax (or anthrax), caused by Bacillus anthracis, have indeed taken place in Siberia in particular. Capable of infecting our species, this bacterium is especially dangerous for herbivores and livestock.
A particularly serious epidemic thus took place in the summer of 2016 in the Yamalo-Nenets Autonomous District and led to the death of 2 reindeer. This epidemic coincided with a particularly hot episode in the Russian Far North… The preferred explanation is that the pathogen was released following the thawing of the carcass of an animal that had died from coal until then caught in the permafrost. In addition to the reindeer, several dozen residents had to be hospitalized and a child died.
Ancient anthrax hotspots identified affecting reindeer in Siberia date back to 1848. During these epidemics, it is often the consumption of dead animals that has caused illness in humans.
Other hypotheses exist to explain these epidemics, such as stopping anthrax vaccination and reindeer overpopulation.
Dangerous for populations at the local level, anthrax epidemics triggered by the thawing of the permafrost should nevertheless not have serious consequences at the global level: anthrax infection of herbivores remains common worldwide. They are therefore unlikely to cause a pandemic.
Re-emergence of old resistances?
Another concern is whether antimicrobial resistant organisms could be released into the environment by the thawing of ancient soils.
Many studies have shown that resistance genes (to antibiotics, etc.) can be detected in permafrost samples. These genes, which bacteria pass on to each other, allow them to become resistant to antibiotics. This is not surprising, since many such genes have evolved from organisms living in the soil.
The environment, particularly at river level, is already strongly contaminated with various resistance organisms and genes. It is therefore doubtful that the bacteria that survived the permafrost will change the situation at this level, especially since the resistors that were useful yesterday are not necessarily useful today...
Encouraging data, but which does not prevent us from being cautious. Each new study brings to light new kinds of viruses capable of resisting time, caught in frozen soils – which encourages us to remain vigilant, without falling into disaster scenarios that no scientific fact has yet come to fuel. .
Paul Hunter, Professor of Medicine, University of East Anglia
This article is republished from The Conversation under Creative Commons license. Read theoriginal article.