New York, March 27 : While previous studies had suggested that bats or snakes may have been responsible for the SARS-CoV-2 or coronavirus transmission, a new study indicates another animal may be the missing link -- pangolins, also called anteaters.
The study, published in the Journal of Proteome Research by the researchers from the University of Michigan in the US, aimed to unearth how the virus first infected humans.
This evidence points to pangolin as the most likely intermediate host for the new coronavirus, but additional intermediate hosts could also be there, the researchers said.
Understanding where SARS-CoV-2 -- the virus that caused the COVID-19 pandemic -- came from and how it spread is important for its control and treatment.
Most experts agree that bats are a natural reservoir of SARS-CoV-2, but an intermediate host was needed for it to jump from bats to humans.
A recent study that analysed the new virus' genome suggested snakes as this host, despite the fact that coronavirus is only known to infect mammals and birds.
Meanwhile, an unrelated study compared the sequence of the spike protein -- a key protein responsible for getting the virus into mammalian cells -- of the new coronavirus to that of HIV-1, noting unexpected similarities.
Although the authors withdrew this preprint manuscript after scientific criticism, it spawned rumours and conspiracy theories that the new coronavirus could have been engineered in a lab.
For the current findings, study researcher Yang Zhang and colleagues wanted to conduct a more careful and complete analysis of SARS-CoV-2 DNA and protein sequences to resolve these issues.
Compared to the previous studies, the researchers used larger data sets and newer and more accurate bioinformatics methods and databases to analyse the SARS-CoV-2 genome.
They found that in contrast to the claim that four regions of the spike protein were uniquely shared between SARS-CoV-2 and HIV-1, the four sequence segments could be found in other viruses, including bat coronavirus.
After uncovering an error in the analysis that suggested snakes as an intermediate host, the team searched for DNA and protein sequences isolated from pangolin tissues for ones similar to SARS-CoV-2.
The researchers identified protein sequences in sick animals' lungs that were 91 per cent identical to the human virus' proteins.
Moreover, the receptor-binding domain of the spike protein from the pangolin coronavirus had only five amino acid differences from SARS-CoV-2, compared to the 19 differences between the human and bat viral proteins, the researchers said.
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