Most common strain of coronavirus found in 85% of all cases worldwide mutated from the original version to be MORE infectious - but not more deadly, study finds
A mutated version of the coronavirus, dubbed D614G, is found in 85 per cent of global cases and researchers believe this version is so common because its genetic modification makes it more infectious and better at spreading.
However, analysis from experts at the University of North Carolina found the change did not make it more deadly or likely to cause severe symptoms.
D614G is by far the most common strain of coronavirus affecting humans worldwide and first appeared in February in Europe.
International travel allowed this variant to spread across the continent and into the Americas, Oceania and Asia within weeks.
D614G mutation is the most common variant of the coronavirus, found in 85 per cent of global cases, and researchers believe this mutant version thrives because its modification made it more infectious and better at spreading
In the early days of the Covid-19 pandemic, the dominant guise of the virus was a variant now called the 'D strain'.
However, the D614G mutation sprung up at one specific location, position 614, on the spike protein of the virus, in a European patient.
This viral spike hijacks the human receptor ACE2 and this is how it infects human cells.
The location of the mutation sits at a critical juncture which affects how the virus cleaves in half after infiltrating a cell.
The mutation is very small and simple, one amino acid is changed from a D (aspartate) to a G (glycine), hence the moniker D614G.
As Italians, Britons and others from coronavirus hotspots travelled to Asia, Australia and America, the D614G virus then took hold in these regions.
Data from a study published last month shows a spike of the G strain in Europe at the start of February, followed by another resurgence of the G variant a fortnight later.
By the start of March, cases of D614G were spotted around the world and this specific mutation made up around a quarter of all cases.
It continued to take over and constituted more than 70 per cent of all cases by May, and the number is now thought to exceed 85 per cent.
Scientists have been trying to determine why the D614G strain emerged as the principle form of SARS-CoV-2, the virus which causes Covid-19.
These graphs show the ascension of the D614G strain over time. The blue line and coloured area shows how common, as a percentage, the D614G is among all coronavirus cases in different continents. The G strain is now by far the most common, supplanting the original variant, all around the world
The orange portion of the graph shows percentage of coronavirus cases which are the original D strain. Blue shows how common the G Strain is. Over time, the G variant supplanted the D strain
The latest study, published in the journal Science, created a lab-built version of the mutant virus and watched how it infected mice and hamsters modified to have the human version of the ACE2 receptor.
ACE2 has been dubbed the 'gateway to the cell' for the coronavirus and the interaction between it and the viral spike is the focus of much research.
Yixuan Hou, lead author of the study, at the University of North Carolina, says the amount of virus an animal became infected with was similar whether it was the D or the G strain.
'However, the D614G variant transmits significantly faster and displayed increased competitive fitness than the wild-type virus in hamsters.
'These data show that the D614G substitution enhances SARS-CoV-2 infectivity, competitive fitness, and transmission in primary human cells and animal models.'
The hamsters with the mutated strain lost slightly more weight than those with the original variant but the authors say it is negligible and that, overall, the D614G substitution does not significantly enhance virus pathogenesis.
The variant did transmit significantly faster in hamsters, which, the authors believe, indicates the virus evolved not for greater pathogenicity, but for better human transmissibility.
These findings, although not in humans, offer some of the most convincing evidence yet that the mutation spread rapidly due to improvements in its transmissibility.
The researchers also used human cells from doors to see if the mutated strain was better at infecting cells and found it was.
Both the ancestral and mutated version were injected into cells and after three days, the G strain was overwhelmingly dominant in the cultures.
This happened 'regardless of whether the [original] virus was at a 1:1 or 10:1 ratio over the isogenic D614G mutant', the researchers say.
While the study confirms the mutation is more infectious, it does not come to a conclusion as to why.
However, a recent study, published on the pre-print server medRxiv and not yet peer-reviewed, from the University of Leuven in Belgium discovered the D614G mutation makes the coronavirus thrive at 37°C, human body temperature.
It is more stable at this temperature than the original D strain, which prefers 33°C.
This difference makes the new variant more stable at the exact temperatures seen in the human respiratory tract.
The mutation is also associated with increased ability to manipulate proteases, enzymes in cells which destroy proteins, to facilitate infection.
'Collectively, our findings indicate how the coronavirus spike protein is fine-tuned towards the temperature and protease conditions of the airways, to enhance virus transmission and pathology,' the academics write.
No comments: