Mutation. A word that scares and ignites imaginations. Popularized by the X-Men, this team of superheroes from the Marvel team, the real mutants have nothing to do with their fictional counterparts. But what exactly do we mean by mutation? All living organisms carry their genetic heritage on a long molecular chain called DNA. In the case of certain microbes, such as the SARS-Cov2 coronavirus, which covers the news, the information may also be contained on another similar chain called RNA. When they reproduce, whether by sexual reproduction (2 parents) or parthenogenetic (only one parent, as in certain insects, reptiles, fish, microbes or plants), individuals transmit this genetic heritage.
When the gametes, the sex cells that will transmit this genetic inheritance to the next generation, are produced, it will be copied, and copied, and copied thousands of times. However, we are talking about genetic works comprising several hundreds of millions of characters (or nucleotides, the human genome comprises for example 3.3 billion. The record is held by a microscopic amoeba Amoeba dubia which counts twice as many…). It turns out that nature is not completely perfect: faced with the colossal magnitude of the task, some copying errors will be made. They are very rare. We are talking about an error per million, even billion, of letters. However, these copies are considered to be mutated versions of the original.
The virus adapts to slightly different hosts
One of the peculiarities of this new virus is that it seems to have a good affinity for human cells. It is for this reason that an individual can be a carrier without developing alarming symptoms and that the virus can remain undetected and go unnoticed for several days. When the virus arrives in a new region of the world populated by humans with physiological and immune characteristics slightly different from those from which it comes, light mutations take place in order to adapt to these new hosts. Obviously, nothing conscious in this process. When a pathogen invades an organism, it multiplies in several copies, slightly different due to the small errors that will occur when copying genetic material. According to Darwinian theory of evolution, only the most apt and best adapted avatars will survive and disseminate. It is therefore not surprising that, as we have read from Italian researchers, compared to the coronavirus from China, ” the Italian version is certainly the result of a mutation, especially since this virus is modifying from person to person “. This says nothing more than that: the virus has adapted to slightly different hosts from each other, to different populations in different countries.
An important element: the scale of the mutation
But, within the framework of the development of a treatment and in particular of a vaccine against this viral threat, the important thing is not that this virus mutates – they all do it – but the scale of this mutation. To get into the human analogy, a virus constantly changes its t-shirt. All the more, when he arrives in a new country. No wonder that, it adapts to the customs in force. These are minor mutations which do not prevent the identification of the virus by medical tests or a future vaccine. On the other hand, that he can change his face, his identity, and therefore that he becomes invisible to treatment, requires many more changes. This cannot be done at once because it requires large-scale changes, of several hundred or thousands of letters.
At present, as estimated by the team of Jian Lu (Peking University) in the March 3, 2020 edition of National Science Review , the coronavirus is divided into two types, L and S. These two populations are are distinguished by their surface receptors, the anchors by which viruses bind to human cells. If the strain S is the oldest, it generated in the early days of infection in Wuhan, the strain L, more aggressive and which developed more quickly, precisely because of this Darwinian competition which wants that or the virus most suited to the host which becomes predominant. Result: at present, the L strain is in the majority and is present at 70% while the S strain is at 30%.
The study also specifies that, faced with global health services, the L strain was subjected to greater selective pressure and could not completely oust its competitor S. Again, nothing surprising: as the L strain generates more rapidly from more seriously ill patients, it was identified and contained more widely. The downside: during this time, the S strain was able to recover from the hair of the beast and spread incognito.
Now what can happen? Can new major mutations occur in SARS-Cov2 to produce other strains, either more aggressive or more infectious? No one can say because the world of viruses remains unpredictable. One thing is certain: the more the virus propagates within the human population and multiplies, the more mutations occur in its heritage and the more the risks of a new strain arising. Hence the efforts made by the health services to minimize the spread of this threat.