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Current Affairs

Coronavirus circulation unnoticed in bats

Date: 04 August 2020 Tags: Miscellaneous

Issue

The novel coronavirus (SARS-CoV-2), which has so far infected over 17.6 million people and killed nearly 0.68 million across the world, has been circulating unnoticed in bats for decades.

 

Background

 Bats have been the “primary reservoirs” for novel coronavirus. The SARS-CoV-2 virus is likely to have diverged from closely related bat viruses called the sarbecovirus, 40-70 years ago.

 

Details

  • In early February, Chinese researchers had found that SARS-CoV-2 is most closely related to RaTG13 sarbecovirus, which was isolated from a horseshoe bat in Yunnan province in 2013.

  • Based on the nearly 96% genome sequence identity between SARS-CoV-2 and RaTG13, a team of scientists said that an origin in bats is probable for the COVID-19 outbreak. 

  • The authors analysed the evolutionary history of SARS-CoV-2 using genomic data on sarbecoviruses.

  • They employed three approaches to identify regions in the virus that had not undergone recombination and that could be used to reconstruct its evolution.

  • All approaches suggest that RaTG13 and SARS-CoV-2 share a single ancestral lineage and estimate that SARS-CoV-2 genetically diverged from related bat sarbecoviruses in 1948, 1969 and 1982, respectively.

  • The novel coronavirus itself has not arisen from recombination of any sarbecoviruses. The ability of the spike protein in the virus to bind to ACE2 human receptors had emerged within bats and is an ancestral trait shared with bat viruses and not one acquired recently via recombination. 

  • The results suggest the presence of a “single lineage” circulating in bats with properties that allowed it to infect human cells. This was also the case with the bat sarbecoviruses related to the 2002 SARS lineage.

  • They conclude that it is plausible that pangolins could have been a conduit for transmission to humans, but there is no evidence that pangolins facilitated adaptation to humans by being an intermediate host.

  • Before pangolins, snakes were thought to have served as intermediate hosts of SARS-CoV-2. But the present study found no evidence to support this hypothesis. 

  • The researchers also caution that the long divergence period raises the possibility of other undocumented virus lineages circulating in horseshoe bats that have the potential to jump from bats to humans.