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Covid-2019: five minutes to understand the challenge of the virus mutation

2020-03-06T18:19:44.780Z


As Covid-2019 has crossed the 100,000 mark worldwide, Chinese researchers suggest in a study that


Coronavirus has spread worldwide for three months. The situation has become very critical in China, South Korea and even Iran, when the 100,000 contamination threshold was reached on Friday. In France, the number of infections exploded this week, going from a few dozen cases to more than 577 cases, including nine deaths. The country has never been so close to stage 3, where there is no longer any question of trying to detect and isolate cases to stop the epidemic, but rather of mitigating the effects.

As virologists and epidemiologists around the world try to learn more about the dangerousness of the virus, Chinese researchers published a rather alarming study on February 29 in the National Science Review. Based on 103 strains of SARS-CoV-2, the virus that causes Covid-2019 disease, Jian Liu, a researcher at Peking University, and his colleagues suggest that the virus has mutated into two different strains , one named “S”, and the other “L”, more aggressive. "Human intervention could have put pressure on the L group, which would therefore have become more aggressive and spread more rapidly," say the researchers.

Mutation or evolution?

Questioned by a journalist on the relevance of the study, Professor Jérôme Salomon, director general of health, estimated Thursday that the virus was not the object of a mutation but of an "evolution". "We will [soon] have data to know if in France we are more on L or S", he added.

In reality, the two terms are very close: “In virology, mutations are the bases of evolution and we use the two terms almost interchangeably. Viruses evolve all the time, accumulating mutations ”, explains Étienne Simon-Loriere, virologist at the Institut Pasteur.

How does the mutation of a virus work?

The genetic information carriers of viruses fall into two groups, RNA (ribonucleic acid) viruses which mutate regularly, such as influenza, Ebola or SARS-CoV-2, and DNA viruses (deoxyribonucleic acid) which mutate less easily, like herpes. "The oldest viruses have remained with RNA genetic support, which gives them advantages, such as a high mutation rate and rapid infection of cells" which prevents the host's immune system from adapting, explains Étienne Simon-Loriere.

To multiply, the virus will attach itself to a cell, then penetrate it and transmit its genome, that is to say all the genes that constitute it. During this process, which is called replication, the virus makes tens of thousands of copies of its genome, and sometimes with errors: "Most of the time, this is inconsequential and it allows us to follow it at the trace, ”said the researcher.

Is this a worrying phenomenon?

Certain viruses sometimes undergo a significant mutation, that is to say which affects the degree of replication and transmissibility (ability of the virus to establish an infection from an infected person to a healthy person).

This is what happened in 2005 with chikungunya on the island of Reunion. Thanks to the mutation of a single gene, the virus has allowed new mosquito species to transmit it to humans. About 250,000 people were infected in 2006 as a result of this mutation.

Why is the article published in the National Science review criticized?

Regarding SARS-CoV-2, there is nothing to confirm that the coronavirus has mutated significantly. "To draw conclusions about the virulence of the virus would be ridiculous. It would take a much larger sample and carry out in vitro confirmations, ”explains Etienne Simon-Loriere.

Especially since the study is no longer really topical: it is based on the analysis of 103 genomes, while we now have 187 genomes, according to Marie-Paul Kieny, virologist and researcher at the Inserm. “These researchers speculate far too much on the dangerousness of the strains. If there were many deaths in Wuhan at the beginning of the epidemic, it is mainly because the Chinese did not know how to manage the disease. It is the difference in treatment from one country to another that has the greatest impact on mortality from the virus, ”she explains.

Does the mutation of the virus complicate the search for a treatment?

For researchers, a minor mutation (the most frequent) does not slow down the search for treatment. Several laboratories are currently testing antivirals to treat the coronavirus: "Unlike chronic infections like HIV which require a combination of drugs, viruses with acute infection like SARS-CoV-2 require only one molecule, but we still have to find it, ”says Etienne Simon-Loriere.

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Another track: five vaccines are currently being studied in Europe, including one at the Institut Pasteur, derived from the measles vaccine. According to the researchers, it will take at least a year and a half to develop a product that is both effective and non-toxic to humans. For the Ebola vaccine, clinical trials alone took a year. This time, the European Commission announced the allocation of 100 million euros to finance research.

Source: leparis

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