Though older, less aggressive ‘S type’ strain seems to be more frequent now than ‘L type’
The novel coronavirus (SARS-CoV-2) has mutated, with two strains in circulation, recent research suggested.
The relatively newer, more aggressive ‘L type’ strain was responsible for the outbreak in China’s Wuhan; but ‘human interventions’ slowed down its spread. The older, less aggressive ‘S type’ strain, however, may now be of increased frequency due to weaker selective pressure, scientists said on March 3, 2020.
Six scientists in China authored a paper in Oxford Academic’s National Science Review journal. The researchers from Peking University, Chinese Academy of Sciences, Shanghai University and other institutes analysed 103 sequenced genomes of the virus from outbreak epicentre Wuhan as well as other parts of China.
The L type was more prevalent in Wuhan than elsewhere in China, the group suggested: Only one of the 27 virus isolated from Wuhan was the S type. The L type was more prevalent before January 7.
The prevalence of cases started reducing in Wuhan after the first week.
High replication rates help the L type transmit faster in humans. So why did its frequency dip relatively in places other than Wuhan? According to the paper:
Since January 2020 the Chinese central and local governments have taken rapid and comprehensive control measures. These human interventions efforts might have caused severe selective pressure against the L type. The S type might have experienced weaker selective pressure by human intervention, leading to an incase in its relative abundance.
Overall variability in the two strains was 4 per cent at neutral sites, but could be up to 17 per cent, “suggesting that the divergence between the two strains is much larger than previously estimated,” the authors said.
They, however, cautioned that their analyses “were based on patchy genomes that were collected from different locations.” More comprehensive studies would help ascertain the difference in the strains.
A joint mission report by the World Health Organization (WHO) and China the last week of February suggested nearly no mutation in the virus: “Whole genome sequencing analysis of 104 strains of the COVID-19 virus isolated from patients in different localities with symptom onset between the end of December 2019 and mid-February 2020 showed 99.9 per cent homology, without significant mutation.”
“WHO laboratory experts and virologists are following up for more information on the findings of this paper,” the United Nations agency told Down To Earth.
Authors of the paper called it a frameshift mutation. “If the virus mutates, it either drifts or shifts. The latter is much more impactful as it may impact the ongoing research for vaccines of therapeutics. However, if it is only a shift, it would not be of much impact purely in the context of research,” Narendra Saini, a microbiologist and an office bearer of Indian Medical Association, told DTE.
The outbreak has infected 94,334 people in 82 countries so far, killing 3,221. Most recent cases have been reported from outside China.
In India, 29 people had been tested positive by March 4 evening, the latest being a resident of Haryana's Gurugram district who travelled to Italy recently.
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