Doctors, epidemiologists and researchers give us different and sometimes contradictory information about Covid-19. We asked for the point of view of Pr Laurent Roux, author of the website “Virology for all”. Interview.
-There are several types of coronaviruses that have been properly identified. Is Covid-19 really new? And how is it scientifically different from the others?
First of all for precision, Covid-19 refers to the disease caused by the virus which was finally named SARS-CoV-2 (in French SARS-Cov-2) in reference to the 2003 coronavirus called SARS-CoV. It belongs to the subfamily Coronavirinae, genus Betacoronavirus. In this genus there are four other human coronaviruses called HCoV-229E, HCoV-OC43, HCoV-NL63 and HCoV-HKU1 known to cause respiratory or intestinal infections generally benign.
These viruses are classified in the same family by molecular biology criteria including the structure of their viral particle, the nature and size of their genome and the way in which gene expression is carried out, i.e. the strategy by which the information contained in the genome is translated into proteins. There are also criteria for the biology of the infection, such as what type of cells they infect. Most of these criteria are closer to CoV-SARS-2 than to the previously described human viruses.
SARS-CoV-2 is new in the sense that it has emerged in the human population in which it has never been described before. It differs from other human coronaviruses of the same genus by genetic information that produces, among other things, proteins that display a different identity to the immune defence system. Thus antibodies that would be produced after infection with HCoV-229E, HCoV-OC43 would not protect against SARS-Cov-2 infection.
-OC43 would not protect against SARS-Cov-2 infection. -It would appear that there are now several strains of Covid-19. Has the “Chinese” virus already mutated?
A strain in virological jargon refers to a virus that was isolated at one time from one place. There are as many strains as there are virus isolates. As far as I know, the strains isolated in China are no different from strains isolated elsewhere in the world, except for point differences that can occur randomly at a very low frequency. These point differences are smoothed in comparisons of multiple isolates to give a “consensus” sequence. For a consensus sequence to change, a mutation or group of mutations must become preponderant as a result of a selective advantage that makes the mutated strain preponderant. These phenomena occur when the virus encounters radically changing conditions of infection, e.g. presence of an effective antiviral drug, presence of strong immunity in the population, etc. The consensus sequence can be changed by the presence of a mutation or group of mutations.
-Doctors and researchers say that Covic-19 first appeared in Wuhan, China, in December 2019. Hence its name. How can we be sure that it does indeed originate from China and that this type of virus was not circulating before?
This statement stems from the fact that SARS-Cov-2 was first detected in Wuhan. We are certain of nothing, except that this virus has never been described before and elsewhere. If it was circulating elsewhere and before, it went unnoticed.
-More than other animal species, wild birds serve as a natural reservoir for the coronaviruses they have helped to spread in the past. Notably avian flu and West Nile flu. Couldn’t Covid-19 have been transmitted from China to other continents via migratory birds?
To my knowledge, wild birds are not a preferred reservoir for Betacoronaviruses, nor for West Nile fever viruses, as is the case for influenza viruses. For SARS-CoV it has been concluded that its natural reservoir could be the bat, and it is currently thought that SARS-Cov-2 may also have been transmitted to humans from a bat species via a small rodent mammal not yet identified with certainty.
-What is the current status of the research on Covid-19? What do we know, scientifically, about this virus that frightens the entire planet?
We know the sequence of its genome base by base (letter by letter), we know how to recognize its genome to make a diagnosis. By analogy with SARS-Cov, we extrapolate knowledge of molecular biology to facilitate the experimental approach. For example, we know that the virus binds the same receptor protein on the cell as the SARS-CoV. Vaccine production is being worked on and millions of molecules are being tested to identify molecules that could destroy the virus or block its multiplication. It has only been two months since researchers have seen the research funds implemented through special funding to try to neutralize this new impediment. Also, the epidemiological and pathophysiological aspect is being closely monitored.