Thursday, April 16, 2020

Shining some light on the natural origin theory of SARS-CoV-2

I am going out on a limb here, since genetics has evolved quite a bit in the decades since I studied it.  I would appreciate readers to comment on arguments pro and con the natural evolution theory of SARS-CoV-2.

While SARS-Cov-2 might have evolved naturally, from bats, pangolins and civets, I have trouble seeing that as very likely.

First, the SARS-CoV family of beta coronaviruses apparently do not cause illness in the bats with whom they coexist. There might even be a symbiotic relationship.  There is no evolutionary advantage for these viruses, which are not normally exposed to humans, to accrue features that provide additional virulence in humans.  

Second, the vast majority of random mutations, in any species, lead to reduced, not enhanced virulence.  There is no survival benefit gained by features that are of no use in a bat milieu.  Additional virulence factors probably means more RNA is needed during reproduction, which would also put the mutated virus at a competitive disadvantage. 

Third, the reason I feel strongly about this is that the SARS-Cov-2 virus has, compared to the original (2003) SARS-CoV virus,  acquired multiple features that have enhanced its virulence for humans.

These are:

1.  The prolonged ability to infect others, even when the infected person is asymptomatic or presymptomatic, extending to the period after they have apparently recovered.  The 2003 SARS (which I will refer to as SARS-1) patient became contagious only when they had symptoms, it is said.

2.  The 3 orders of magnitude greater viral titres in the nasopharynx of affected individuals, compared to titers reported from SARS-1

3.  Increased virulence in terms of the increased number of organs the virus is able to infect (a.k.a. enhanced tissue tropism) of SARS-2 compared to SARS-1

4.  Not certain about this one, but there is limited evidence that SARS-2 persists a bit longer on environmental surfaces than SARS-1.

It seems that none of these features would help a bat virus outcompete its viral competitors.  Together, the presence of multiple, additional virulence factors would presumably require even more RNA, putting the mutated bat virus at a considerable disadvantage to its peers.

Update April 29:  Newsweek has been delving into "gain of function" (which means increasing the virulence of a pathogen) coronavirus research in Wuhan, China which might have contributed to the formation of SARS-CoV-2... and the interesting fact (which I posted about here) that the US government provided financial support for this research.  Newsweek's pieces were posted April 27, and 29.  My other pieces questioning the origin of SARS-CoV-2 are here and here.


Anonymous said...

Democracy Now had a long interview with Peter Daszac who takes a different view. He basically said, if I understood him correctly, that there is no way the virus started in a laboratory.
The transcript is up at DN. I'd like to hear your appraisal.

Meryl Nass, M.D. said...

Peter Daszac directs EcoHealth Alliance. This organization was a pass-through for funding that came from USAID's Predict program and went to Dr.Zhengli Shi's laboratory, via EHA.

He says he worked and collected bats with the researchers in Wuhan. His livelihood depends, in part, on such programs continuing. Little surprise he would be so adamant that the source of the virus was not a lab he had funded and worked with.

SBH said...

Safety concerns at WIV

SBH said...

PS Shi is a "she."

Meryl Nass, M.D. said...

I was referring to Peter Daszac in my comments, not to the female Chinese coronavirus lab director. He has worked with her lab and provided funding for her lab.

J.C. on a bike said...

Please check the blog Harvard to the BigHouse, and my YouTube summary of this story here:

Thanks! You are right! We started covering the primary literature supporting this theory in Jan.