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Endre Szvetnik By Endre Szvetnik • June 10, 2020

COVID-19 FAQ: how did a virus from horsehoe bats find a way to infect humans?

US scientists have uncovered why the novel coronavirus (SARS-CoV-2) that originated in horseshoe bats acquired the ability to start infecting humans and not just the winged mammals themselves.

A bat coronavirus has a 96.3% genetic match with SARS-CoV-2 but this alone did not enable it to infect humans

In a recent study, University of Texas and New York University teams confirmed that the ‘parent’ of SARS-CoV-2 – RaTG13 was first identified in bats in 2013. RaTG13 shares a 96.3% genetic similarity to the novel coronavirus currently causing a pandemic among humans. But crucially, its structure did not enable it to penetrate and infect human cells lining the lungs and the gut, or, in other words, make the ‘jump’ to people. This was because the notorious ‘spike protein’ in RaTG13 was not the right shape to bind to the entry point on human cells (the often-mentioned ACE2 receptor).

How did then SARS-CoV-2 evolve to attack humans? The researchers suspected that an ‘intermediate host species’ was involved in its evolution, as was the case with the MERS virus. MERS was first identified in 2012 and it emerged after a bat coronavirus recombined with one found in camels. From them the virus passed on to humans. In the case of the bat coronavirus (RaTG13) that was very similar to the current SARS-CoV-2, the recombination occurred through a coronavirus found in pangolins. Pangolins are an endangered species. They are illegally trafficked because of beliefs that their scales and meat can help treat cancer, asthma and arthritis, aid kidney function and lactation. Previous research has identified SARS-like coronaviruses in pangolins.

The teams from the University of Texas and New York University have compared the genetic codes of the RaTG13 bat coronavirus and SARS-CoV-2 to the codes of two pangolin coronaviruses. They found so-called ‘recombination breakpoints’ in SARS-CoV-2. These breakpoints are sections in the genome which contain code obtained from other viruses.

In the case of SARS-CoV-2, the code is a combination of the very similar RaTG13 bat and the two pangolin viruses. Importantly, the result is a combination of the similarly structured bat coronavirus and the spike protein of the pangolin viruses that make human infection possible. The researchers were unable to explain how the actual first transmission of the virus from animal to human happened, but warn that limiting direct human contact with wild animals would be critical in preventing future diseases that are caused by coronaviruses found in animals.

Here is the current state of science on a Sparrho pinboard.

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