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Old 25th February 2021, 01:19 PM   #116
Sherkeu
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Join Date: Jan 2011
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Originally Posted by lomiller View Post
Covid-19 enters humans cells by binding to ACE2, but it doesn't bind efficiently to the bat version of ACE2 so it would have a lot of difficulty infecting bats. This effectively rules out the possibility that it's binding mechanism evolved in bats. Conversely the Covid's closest know relative, RaTG13 can't bind efficiently to human ACE2 so neither have much chance to jump directly between species.

Another important factor is that the changes that allow Covid to bind to human ACE2 appear to come from a Pangolin virus Pangolin-CoV-2019 via a recombination event. This event could have occurred in some animal other than a Pangolin, but it must have involved exposure to a Pangolin.

The scenario where the recombination happened in yet another species would require 2 different viruses to jump species and infect the same individual which is less likely than one virus jumping to a Pangolin then recombining with a virus that commonly infects Pangolins.
I've read conflicting things on this. Some assert that the pangolin is just a victim rather than a vector...but I am not knowledgeable enough to compare theories. They have a 2013 bat virus in Yunnan, and an early 2019 pangolin virus from a confiscation in Guangdong that are most similar to the human virus. What happened in late 2019 though remains unknown. That bat virus doesnt infect that pangolin and infected pangolins did not transmit to their human carers over months of close proximity (or so they said).

The lab in Wuhan created chimeras to replicate how it could jump to humans (paper was in 2015). They had animals there with in vivo experiments. Not much is said about that since the pandemic began. I take their word when virologists say they can tell when things are spliced into a genome, and that Covid has no evidence of it.

There are a lot of pieces missing. Might be too late to find them now.

Last edited by Sherkeu; 25th February 2021 at 01:24 PM.
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