Published: 18:23 EDT, 23 September 2020 | Updated: 04:05 EDT, 25 September 2020
Experts examined more than 5,000 genomes from viruses recovered in the earliest phase of the pandemic in Houston. These were compared to samples taken from a recent wave of infections.
The study, which was not scrutinised by fellow scientists before publication, found that 99 per cent of all strains in the second wave had a mutation, known as D614G. For comparison, it was only found in 70 per cent of samples taken during the city’s first outbreak, suggesting it has pushed out competitive strains.
Studies have shown the mutation boosts the number of ‘spikes’ on the crown-shaped virus. The spikes are what allow the virus to bind to and attack cells, increasing the ability of the mutated virus to infect cells.
Academics at Houston Methodist Hospital – who carried out the first-of-its-kind study – said patients infected with the variant strain had significantly higher amounts of the virus when they were first diagnosed.
But they found little evidence mutations in the SARS-CoV-2 have made it deadlier, noting that severity of COVID-19, the disease caused by the virus, was more strongly linked to patients’ underlying medical conditions and genetics.
They also said some regions of the spike protein – the primary target of coronavirus vaccines now in development – showed several mutations, possibly indicating that the virus is changing in order to evade the body’s immune response.
Previous studies have shown the coronavirus is mutating and evolving as it adapts to its human hosts. Scientific theory suggests viruses may become weaker over time in a bid to survive – if they kill or cripple all their human hosts they will run out of road.
Scientists around the world noted as early as May that the D614G strain had become dominant in most counties with high coronavirus case numbers, including the US.
Houston Methodist Hospital researchers found that more than 99% of people in the Texas city who caught coronavirus in the second wave had a variation of the virus with a mutation known as D614G that codes for more spike proteins, making the virus more infectious
Texas is now in its second wave of coronavirus, and some 30,000 new cases are being reported a day
The study by the Royal Society’s SET-C (Science in Emergencies Tasking – COVID-19) task force also studied the one major mutation SARS-CoV-2 underwent.
It is located on the S-protein which sticks out from the surface of the virus. This spike latches on to the ACE2 receptor of human cells, tricks it into opening the cell, and allows the pathogen to infect a person.
At one specific location — residue 614 on the S1 terminus — the original form of the coronavirus had the amino acid aspartate, labelled with a D.
However, a random mutation saw this amino acid replaced with a glycine, labelled with a G.
The so-called D614G mutation was seen in barely any samples taken in February. However, by March, more than a quarter (26 per cent) of isolated SARS-CoV-2 strains contained the mutation. By May this figure had reached 70 per cent.
The D614G mutation is the most dominant one seen globally. This mutation appears to help more virus infect a person and for more efficient infection of cells.
The D614G virus is also almost always accompanied with three other minor mutations. The role of these changes remains unknown.
It swiftly rose to the top of the viral food chain in New York City, Italy and the UK, while the West Coast of the US was primarily battling a strain thought to be 10 times less infectious than D614G.
Instead, sunbelt states like Texas, Arizona and Florida became the hardest-hit in the nation in the late spring and summer.
Texas is still reporting nearly 3,000 new infections a day, as of Wednesday, and more than 100 daily fatalities.
Public health experts believe the state is now its second wave of coronavirus, and Harris County – where the sprawling metropolitan of Houston is located – continues to be the hardest hit.
And the new study, posted to the online pre-publication repository, MedRxiv.org, provides a clue as to why.
The D614G strain of coronavirus is characterized by portions of the viral genome that code for modifications to the spike protein.
The ‘G’ portion, in particular, was found in 99 percent of samples tested by the Houston Methodist scientists.
‘Strains with a Gly614 amino acid replacement in the spike protein, a polymorphism that has been linked to increased transmission and in vitro cell infectivity, increased significantly over time and caused virtually all COVID-19 cases in the massive second disease wave, the study authors wrote.
They added the patients who had this variation of the virus had much higher viral loads in their noses when they tested positive for COVID-19.
And in the lab, neutralizing antibodies that might stop other strains of coronavirus from infecting human cells had less effect on the D614G variant.
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World news – US – More contagious coronavirus strain is dominant in Texas’s second wave