COVID-19 has affected over 28 lakh people in India so far. Out of this, about 54,000 have succumbed to the disease while more than 20 lakh have already been cured.
Lockdown and social distancing have led the SARS-CoV-2 virus to develop specific mutations in various areas to adapt to host populations, which is important for the survival of the virus.
Now, a group of researchers at the JIS University, Kolkata say that in an attempt to survive, the COVID-19 causing virus may have gained some mutations that have weakened it over time and reduced the COVID-19 fatality rate in the country. As per the study, the fatality rate in India has gone down sevenfold from April 11 to June 28, 2020. The study is still in the preprint phase and not peer-reviewed yet.
Spike protein and viral mutations
From what is known so far, SARS-CoV-2 virus uses something called a spike protein present on its surface to identify ACE2 receptors on host cells. This protein has two subunits - S1 and S2. The receptor-binding domain (the area that actually binds with ACE2) is present on the S1 subunit. However, experts believe that more areas in both the subunits may be helping with the attachment somehow.
Spike protein mutations would hence have some effect on the infection.
To understand the mutations in spike protein in SARS-CoV-2 and its effects on the disease, the researchers took the genome of the COVID-19 causing virus from 630 isolates in India.
It was found that the stability of spike protein and ACE2 complex has a direct correlation with disease severity. The more stable the binding the more severe the disease.
In India, the coronavirus diverted into two evolutionary lines from the original Wuhan-Hu-1/201 strain and its descendant D614G variant.
Wuhan-Hu-1/201 led to the formation of 20 different strains, out of which one further evolved to the three different strains that were isolated from Bihar, Tamil Nadu and Telangana. On the other hand, D614G variant led to the formation of 47 different variants. A total of at least 16 variants of the spike protein were found in the tested samples. About 53% of all these isolated variants of coronavirus were only found in India and over 2/3rd of all variants had reduced stability in their spike protein-ACE2 complex.
About 70% of all samples were from either Maharashtra, Gujarat, Telangana or Delhi. The isolates showed a direct correlation between the fatality rate and spike protein-ACE2 stability. Delhi and Telangana had a 7% fatality rate with an average stability index value while Maharashtra and Gujarat had an 8 and 9% fatality rate with a higher stability index.
Muller’s ratchet is a concept given by the American Geneticist Hermann Joseph Muller. As per this concept, asexual organisms (those that do not multiply through sexual reproduction) tend to accumulate deleterious (harmful) mutations over time, which leads to the extinction of the said organism.
Generally, when an organism mutates, it only keeps useful mutations (those that help it survive) and leaves all the harmful ones. However, when there is pressure to survive, harmful mutations tend to stay.
Experts have suggested previously that Muller’s ratchet may ultimately lead the coronavirus to its extinction.
For more information, read our article on Viral Mutations: FAQ.
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