In early 2020, a small mutation in the spike protein of SARS-CoV-2 saw the light in some corner of Europe . A priori, it was nothing special, nor surprising. All viruses mutate. Some, in fact, mutate a lot in a give and take between chance and natural selection that are consolidating small genetic clockwork pieces capable of doing really prodigious things: from producing their own electricity to causing a global pandemic.
This was the case with that particular mutation, the one we know by the name of D614G; a mutation capable of spreading around the world in a truly surprising way, replacing many other lineages of the virus that had been circulating around the world for months. The history of this mutation is, in large part, the history of the pandemic. A story that is still incomplete, but that is helping us to illuminate areas of the coronavirus crisis that, until now, were hardly visible.
The mutation that conquered the world
One of the obsessions of geneticists throughout the pandemic has been to trace the virus, to affiliate it, to articulate in one way or another a story of how it has moved through the world, how variants have emerged and how they are related to each other. This is what has put us on the trail of the D614G mutation .
This mutation was not in early Asian shoots or, if it was, it did not play a major role in them. According to Palmer and his team , the analysis of the 28,000 sequences of the virus available in May clearly shows that before March this mutation was practically non-existent. In a couple of months, by June 2020, D614G was already in 74% of all published genetic sequences .
This brought a lot of attention to her. As Hodcroft and his team point out , the reconstruction of the dynamics of the virus suggest that this variant originated in Europe during the outbreaks of March and April and dominated the expansion through the European continent and America, displacing the previous lineages that circulated around the world. for months.
Finding this out has led experts to suspect that the D614G variant was more transmissible ( Korber et al., 2020 ; Volz et al., 2020 ) than the Asian variants that we had studied at the time. The “macro” data (and clinical evidence) matched this idea , but laboratory confirmation was not lacking.
A few days ago, Palmer’s team presented a study to find out if, as it seemed, this mutation improves the replication of the virus in the epithelial cells of the lung and in the primary tissues of the respiratory tract. What they found is that, interestingly, mice infected with these variants had a higher viral load in the upper respiratory tract, but not in the lungs .
This supports previous evidence that D614G increases viral load in the upper respiratory tract and thus may increase transmission. Some authors are also convinced that this (the lower presence of the virus in the lungs) is related to a lower virulence . However, we are still far from being able to demonstrate this experimentally.
Is this the famous ‘Spanish strain’?
In recent weeks, a report developed by the CSIC and the University of Baselfound has a new strain of the virus (called 20A.EU1) that, according to their analyzes, emerged in Spain at the beginning of this summer and has spread by various European countries. Specifically, the researchers found the strain for the first time in June and it escalated in a few months to reach 40% of the country’s infections .
“Outside of Spain the frequency of this variant has increased from very low values before July 15 to 40-70% in Switzerland, Ireland and the United Kingdom in September,” they explain while stating that “it is also prevalent in Norway, Latvia, the Netherlands and France “. This “Spanish strain”, as some English media have called it , is one of the strains with the D614G mutation, but it is one of many .
We do not know why it has spread all over the world with this ease . As the same authors acknowledge, “it is not clear whether the rapid spread of any of these variants is due to particular demographic characteristics, the properties of the virus or simply by chance.” In the coming months it will be very important to understand what has happened to this strain in order to spread throughout Europe so effectively.