More than 20,000 years ago, the peoples of East Asia had to face a coronavirus epidemic that left in their DNA the genetic traces of a long forced coexistence. A study published in Current Biology reconstructs those circumstances and shows that human coronaviruses capable of causing serious disease are not just a threat in the last 20 years.
In the past two decades, we have gone through three epidemics caused by Betacoronavirus, human coronaviruses capable of causing serious diseases, such as SARS-CoV, which originated in China in 2002 and killed more than 800 people; MERS-CoV, the coronavirus Middle East respiratory syndrome virus, which claimed the lives of 850 people; and finally SARS-CoV-2, which has caused so far beyond 3.8 million deaths.
Now a study on the evolution of the human genome, conducted by the University of Arizona, University of California San Francisco and University of Adelaide (Australia), brings to light another, much older coronavirus epidemic located in East Asia, in area now occupied by China, Japan, Mongolia, North Korea, South Korea and Taiwan.
‘All genomes constantly accumulate mutations, most of which are harmless and do not lead to changes in gene function. We can imagine the frequency of mutations as a constantly ticking genetic clock ”, explains a Focus.it Kirill Alexandrov, one of the authors of the study. ‘However, when there is selective pressure, some genes’ clocks start ticking faster as they accumulate beneficial mutations. Our study showed that, over 20,000 years ago, many human genes that SARS-CoV-2 uses to manipulate the body’s cells began ticking more rapidly simultaneously, as if to indicate that there was a viral pandemic caused by a similar virus “.
Old acquaintances. Scientists used data from the 1000 Genomes Project, the largest and most detailed catalog of human genetic variability, to observe how human genes that code for proteins capable of interacting with SARS have changed over time. CoV-2. Separately, they also synthesized human proteins and proteins typical of coronaviruses, such as spikes, and showed that these interact in a direct way, and that in fact the way to attack the cells of the viruses of this family has been conserved over time.
Mutual adaptation. By studying how the human genome evolved in regions that encode proteins that interact with these pathogens, the team concluded that, more than 20,000 years ago, the ancestors of today’s East Asian populations faced an epidemic. caused by a coronavirus that caused a disease similar to covid, or in any case by a virus that attacked cells with the same mechanism.
During the epidemic, natural selection operated on the human genome by favoring, as in a form of adaptation, genetic variants capable of leading to a less serious disease. Because it is true that viruses evolve, but we do too. “The modern human genome contains evolutionary information that allows us to go back to tens of thousands of years ago, as if we were studying the rings of a tree to get information on the conditions it went through in the growth phase,” explains Alexandrov.
Sometimes they come back (hopefully not). In principle, proceeding with this type of analysis could compile a list of viruses, or at least virus families, that have caused large-scale outbreaks in the past, and that could do so again throughout history.