There was already a coronavirus epidemic 25,000 years ago
About 25,000 years ago there was an outbreak of a virus linked to the current coronavirus among the inhabitants of East Asia. The article by El Pais
A genetic study – writes El Pais – has found an adaptation to a respiratory virus in people whose ancestors come from East Asia.
About 25,000 years ago there was an outbreak of a virus linked to the current coronavirus among the inhabitants of East Asia. This is the main conclusion of a study that found the signal of that epidemic event in the genome of people today. The method used in this research could be used to investigate other pathogens from the past.
Humans and viruses have been at war for thousands of years. On them, pathogens exert pressure on the host which leaves its mark in its genes. But looking into the past of this interaction isn't easy for two reasons. On the one hand, human DNA does not keep very well and is less easily recoverable, even if the progress of science allows us to go back more and more centuries or millennia. On the other hand, the vast majority of pathogenic viruses are RNA and this genetic material deteriorates very easily and quickly. For this, for example, RNA vaccines require extreme storage conditions.
Now, a group of Australian and American researchers has devised a new method that uses genetic data from current humans and current viruses to open a window into the past. The work, published in the scientific journal Current Biology, examines the interaction between viral proteins, such as the S spectrum of SARS-CoV-2, and human proteins. Either by facilitating the virus cycle or by fighting it, some of these organic molecules and not others interact with some viruses and not others. Humans have more than 22,000 types of proteins that are the basis of the organism. It is estimated that 20%, about 4,500, come into contact with some of the hundreds of viruses that prey on humans. Those that are bound to the most proteins are influenza (around 1,505) and HIV (with 1,209).
Kirill Alexandrov is co-author of this research and explains in an email: “SARS-Cov-2 proteins interact with more than 300 human proteins. Of these, 42 show a powerful signal of adaptation some 900 generations ago ”. This signal appears in the form of changes in the genes that encode these proteins, changes that have propagated by large groups of a given population.
“All genomes constantly accumulate mutations, most of which are harmless and cause no changes in the function of the genes they affect,” says Alexandrov. “We can see the mutation rate as a genetic clock that is constantly ticking. However, when there is selection pressure, some genes' clocks start ticking much faster as they accumulate beneficial mutations. This happens because people with beneficial mutations in their genes survive better in a pandemic than people without. As a result, these adaptive mutations accumulate in the population, ”explains this researcher from the Alliance for Synthetic Biology of Queensland University of Technology (Australia) and CSIRO (Australian counterpart of the Spanish CSIC).
Such an accumulation of mutations has been detected in groups of current humans whose global genetic data is collected by the 1,000 Genome Project, the largest catalog of human genetic variations observed to date. But not in all: of the 26 large populations studied, five have observed it in East Asia, in particular among the genomes of the Han and Dai ethnic groups, both in China. "By comparing a large number of sequenced human genomes, it was shown that more than 20,000 years ago the clock of many genes that SARS-CoV-2 uses to interact with human cells began ticking faster simultaneously, possibly indicating that there has been a viral pandemic caused by a similar virus, ”says Alexandrov.
They recognize that it could have been another virus, but they are convinced that it also belonged to the subgenus of sarbecoviruses, the same subgenus to which the current coronavirus belongs. David Enard, an ecologist and evolutionary biology expert at the University of Arizona (USA), says: “We can link the selection signals of protective variants because they occur in some human genes known to physically interact with coronaviruses and influence their replication. We looked at other genes interacting with other viruses and didn't find the same selection signals, ”explains this study co-author.
Enard has been collecting pairs of interactions between human proteins and viruses for years. He is considered a pioneer in the study of the viruses of the past by reading the current genomes. Three years ago he had already pointed out the exchange of protective genetic variants between Neanderthals and modern humans. David Castellano, of the Center for Genomic Regulation, has collaborated with Enard in the past. "I was already doing research with other viruses and bacteria, such as the plague," he says.
“Even if there are no remnants of what happened, human beings are a repository of the past,” recalls Castellano. And in this repository that is the genome, there are some signals that stand out from the rest. This researcher gives two examples: the changes that allowed adults to continue producing lactase, the enzyme that metabolizes lactose in milk, or the genetic variations that allowed different populations to adapt to the availability of oxygen at high altitudes. "Viruses, pathogens in general, create a signal in the genome that is even stronger," he says.
This is the same idea of Hugo Zeberg, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Germany: “Infections leave their mark on the genome. In fact, they are considered as one of the main driving forces of evolution ”. Zeberg, who did not participate in the latter work, gives an example: “The partial resistance to malaria which is present in the populations where this disease is endemic. It can be said that the immune system is in equilibrium with the pathogens that surround it, constantly adapting to infectious threats ”.
Does this mean that the populations of East Asia would be better protected against coronaviruses? Although the genetic factor may predispose it, it would have less weight today than in the past. Alexandrov comments: “It makes sense that a population selected for a disease is more resistant to it than populations that are not. But current social factors, such as the general health of the population, the structure of health systems, government measures, population density, behavioral patterns and many other epidemiological aspects probably play a much larger role than the previous genetic adaptation ”.
(Extract from the Epr press review)
This is a machine translation from Italian language of a post published on Start Magazine at the URL https://www.startmag.it/mondo/epidemia-coronavirus-25mila-anni-fa-asia-orientale/ on Sat, 26 Jun 2021 06:00:34 +0000.