A mutated strain of the SARS-CoV-2 coronavirus which causes Covid-19 may be more infectious than the original version.
A study of more than 5,000 Covid-19 patients in Houston, Texas revealed 99.9 per cent of infections were caused by this altered version of the virus, called D614G.
The finding adds credence to the theory the mutation is more contagious than the original strain which emerged in Wuhan last year
Outside of the US city, D614G is also by far the most common strain around the world, accounting for 85 per cent of cases globally.
Scientists are trying to determine why the D614G strain has become the principle form of SARS-CoV-2, and think it may be due to the mutation increasing the amount of virus in the upper respiratory tract.
This makes it more likely to spread when the infected person talk, coughs or sneezes.
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This graph shows the distribution of both D and G strains in the Houston study over time. The red and blue waves at the bottom show the amount of cases at any given time and which variant they are. Red is the mutated G strain and blue is the original blue strain. The dotted line at the top shows the percentage of cases over time that have the D614G mutation
D614G emerged first in Europe in February 2020 became more prevalent. But by March accounted for more than a quarter of cases and more than 70 per cent by May. The estimated global figure is now in excess of 85 per cent. The orange portion of the graph shows the prevalence of the original D strain and blue shows how common the G Strain is over time. As the pandemic progress, it made up a larger percentage of infections
Scientists are trying to determine why this strain has become the principle form of SARS-CoV-2 and think it may be due to the mutation increasing the amount of virus in the upper respiratory tract and therefore being more contagious
In the early days of the Covid-19 pandemic, the dominant guise of the virus was a variant now called the 'D strain'.
However, in February 2020, the D614G mutation sprung up at one specific location, called position 614, on the spike protein of the virus.
This 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.
It is believed the D614G strain emerged first in Europe in February 2020 and spread quickly, accounting for more than a quarter of cases globally by March and more than 70 per cent by May.
The estimated global figure for this strain is now in excess of 85 per cent, while a September study from the US found 99 per cent of cases in a New York hospital were of the G strain.
SARS-CoV-2, the virus which leads to Covid-19, has a protein on its surface which binds to a receptor on cells called ACE2 and this is how it invades the body
The latest study, which has been published in the peer-reviewed journal mBIO, found that during the initial wave of the pandemic in the spring, 71 per cent of cases were D614G.
When the second wave of the outbreak hit Houston during the summer, this variant had leaped to 99.9 per cent prevalence.
'The virus continues to mutate as it rips through the world,' says co-author of the Houston study Dr Ilya Finkelstein from the University of Texas at Austin.
The research was led by the Houston Methodist Hospital.
There is much debate over why the D614G mutation became dominant but the prevailing theory is that it is more infectious than the original version.
While the new research was not able to prove that having more virus in the upper respiratory tract makes it more likely to spread, several studies have hinted that the D614G mutation is more contagious.
In August, Paul Tambyah, senior consultant at the National University of Singapore and president-elect of the International Society of Infectious Diseases, made headlines when he said D614G makes the virus more infectious but less deadly.
The study by the Royal Society's SET-C (Science in Emergencies Tasking – COVID-19) task force also studied the one major mutation