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Where did SARS-CoV2 come from? (a THREAD)
The answer is... We don't know! (you should get used to it). But we can hypothesize. Let's tackle the first thing: laboratory escape is not supported by any evidence we have. (1/n)
The answer is... We don't know! (you should get used to it). But we can hypothesize. Let's tackle the first thing: laboratory escape is not supported by any evidence we have. (1/n)
Quite the contrary, our knowledge about coronaviruses and evidence we have so far points in the direction of a natural host.
That is not the first epidemic caused by a coronavirus (look up SARS and MERS) and scientists were expecting something like that to happen again (2/n)
That is not the first epidemic caused by a coronavirus (look up SARS and MERS) and scientists were expecting something like that to happen again (2/n)
Have you seen the quote 'Every disaster movie starts with someone ignoring a scientist'? Yeah...I should ask for a t-shirt like that for my birthday.
Bats are natural reservoirs of coronaviruses and we have many hints which point at them to be our source.(3/n)
Bats are natural reservoirs of coronaviruses and we have many hints which point at them to be our source.(3/n)
The closest genetic match found so far between SARS-CoV2 and other coronaviruses was one found in bats. Although we are still not sure if the similarities are close enough. (4/n)
There is a chance that in fact, original spillover happened between bats and some other animal and then our mystery animal and human.
(5/n)
(5/n)
Long co-evolution between a pathogen and a host can lead to lower pathogenic effects (but don't get all excited about the current pandemic yet, and that our coronavirus will get less pathogenic. That takes years if not decades, and in fact can go both ways). (6/n)
The perfect intermediate host should not have any symptoms upon infection. As some of you remember another theory that appeared in the media some time ago was that SARS-CoV2 came from the pangolins. (7/n)
Genetic links were weaker than in the case of a bat. Apart from the receptor-binding domain, which seems to be really similar to the one found in the human virus. But pangolins seem to get sick and die when infected with SARS-CoV2 (8/n)
and there were no coronaviruses found in pangolins in their natural population... Of course, that doesn't mean that they can't be intermediate hosts, but it makes it more unlikely. (9/n)
Similarities between coronavirus found in confiscated pangolins and humans might be caused by recombination (when two related viruses exchange parts of their genetic material), or convergent evolution (independent evolution of similar traits in different species).
(10/n)
(10/n)
What's the answer then? When will we know? I wish I can tell you but there is a strong chance that we will never know. Several years passed since the big Ebola outbreak and we still do not know where the spillover happened even with this pathogen(11/n)
We knew that pandemic will happen sooner or later. Urbanization and deforestation are stresses which have shown to destroy the natural balance in the ecosystem and promote the appearance of new pathogens in the human and livestock population. (12/n)
Huge livestock industries and animal trade give the virus an opportunity to jump to new species.
It is extremely important to prevent future outbreaks and knowledge about primary reservoirs would help but for now, we should do the things we can(13/n)
It is extremely important to prevent future outbreaks and knowledge about primary reservoirs would help but for now, we should do the things we can(13/n)
We need global international surveillance of the epidemic threats. And we need to invest in science. I just hope that we can learn from what have happened and it will be a wake-up call. And people will stop ignoring scientists;) But also in this case, only time will tell.(14/n)
if you want to know more about the possible sources of SARS-CoV2 here is a very nice review @sci_questions :) https://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(20)30348-7?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0169534720303487%3Fshowall%3Dtrue&fbclid=IwAR2ej6grR0V3GNyFhLXD390Vfj48P8TCBD31aQUnNHwXeV9Mfj-cxbc-S3Mby
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