To eradicate or control coronavirus – via a vaccine or any alternative method – the biggest fight has to be against the A2a type of SARS-CoV-2 virus, said researchers from the National Institute of Biomedical Genomics.
As the virus was carried by travellers from China, the O-type of the coronavirus initially spread to other global regions. Then, the virus evolved in China, as well as outside the country. In each geographical region, many different types of SARS-CoV-2 came up, and began spreading rapidly during January and February this year. However, in most geographical regions, only one type (A2a) of SARS-CoV-2 started to overtake other types.
“A mutation sometimes enables the virus to transmit more efficiently and infect more people,” Partha Majumder, Emeritus Professor at the National Institute of Biomedical Genomics, Kalyani, told The Indian Express. “Such mutant viruses then increase in frequency and can sometimes completely replace the original type of virus in a community or geographical region. The SARS-CoV-2 is doing just this, as has been recently discovered. By the end of March, this A2a type had nearly replaced all other types and become a dominant type of SARS-CoV-2.”
By using RNA sequence data being deposited in a public database – GISAID (www.gisaid.org) – by COVID-19 researchers from around the world, Majumder, who is also president of Indian Academy of Sciences, has been tracking the evolution and spread of the virus, along with co-researcher Nidhan Biswas. Researchers have found that because the A2a type is so efficient in transmitting, COVID-19 has become so prevalent and widespread.
In their paper – Analysis of RNA Sequences of 3,636 SARS-CoV-2 Collected from 55 Countries Reveals Selective Sweep of One Virus Type – to be published in the second special issue of the Indian Journal of Medical Research, they noted that like all viruses, this coronavirus has also evolved into new types over time and during its spread to different global regions from Wuhan in China.
Based on the changes acquired in the genome, this coronavirus can be classified into many types – O, A2, A2a, A3, B, B1, and so on. Currently, there are 11 types, of which O is an ancestral type; the type that was originally reported from China in December 2019. The remaining ten types have evolved over time, as the virus spread. One or a few mutations define the signature of each of these types.
According to the researchers, the A2a type has acquired a change in its RNA sequence that alters a component (an amino acid alteration from aspartic acid to glycine) of the spike protein, at position number 614, of the coronavirus. “When the coronavirus infects a person, it enters the lungs and makes millions of copies of itself there. As a result of the huge load of the virus in the lungs, the infected person falls ill, has enormous breathing difficulty and sometimes dies. The spike protein plays a major role in the coronavirus infecting a human by entering lungs. To infect, the coronavirus has to first anchor itself to a lung cell. Human lung cells produce a protein called ACE2 on their surface. The spike protein of the coronavirus first clings on (binds) to this surface protein ACE2. Then another protein takes action and promotes the entry of the virus into the lung cell. The more efficiently a type of virus can bind and enter, the more successful it will be to propagate itself. The A2a type of the coronavirus has gained this efficiency because of the amino acid change to glycine from aspartic acid. All other types of SARS-CoV-2 possess aspartic acid. The change to glycine enables the A2a type of the coronavirus to enter lung cells in larger numbers,” researchers said.
A team of scientists from the National Institute of Biomedical Genomics is also investigating why despite the presence of the A2a type, other types also co-exist.
The Department of Biotechnology, Government of India, is spearheading a pan-India effort to coordinate the sequencing of a large number of viral genomes and relate the type as well as other genomic features of SARS-CoV-2 with clinical features of the infected persons to understand the nature and extent of host-virus interaction. While each country has registered a high prevalence of SARS-CoV-2 infection, there are regional differences in frequencies of different types of the coronavirus. Dr Renu Swarup, DBT secretary, said it was unclear whether these regional differences are because of differences in patterns of travel of residents or visitors, or whether these are because of differences in ethnic composition. Large-scale sequencing of SARS-CoV-2 is essential, because it is likely that this virus also mutates rapidly as the influenza virus.
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