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WIV-1 can infect human cells in vitro. No complete human infected with WIV-1 has ever been identified, living or dead. When SARS-1 emerged in humans, cases were

WIV-1 can infect human cells in vitro. No complete human infected with WIV-1 has ever been identified, living or dead. When SARS-1 emerged in humans, cases were concentrated among traders handling civet cats, as were positive antibody tests. That seems to me like a pretty strong case for forward zoonosis, maybe not perfect but certainly stronger than any evidence we have for SARS-CoV-2. I agree there's no evidence for any animal except bats as the reservoir for SARS-1 (or SARS-CoV-2). The intermediate host seems like the important link to show natural origin, though. Genetic engineers can't invent new viruses de novo, only modify existing ones, so a reservoir host must always exist; the question is just how it got from that reservoir to a human pandemic.

sudosysgen 4y ago
If SARS-1 was more infectious and less virulent you wouldn't see cases concentrated amongst traders, would you? If anything, since many of them already have some kind of immunity from previous infection, you would not expect them to even notice being sick before the virus already infected thousands.
- tripletao 4y ago
  I agree that finding the origin of a virus that's less deadly and faster-spreading (like SARS-CoV-2) is a harder problem. Nevertheless: 1. We quickly found pretty good evidence (infected civet cats and raccoon dogs, and infected human traders of those animals) that SARS-1 arose from natural zoonosis, within about a year of its emergence in humans. The later discovery of WIV-1 didn't add to this evidence. 2. We've found no such evidence for SARS-CoV-2. That doesn't mean SARS-CoV-2 definitely arose unnaturally--we've expended a lot more effort looking, but it really is a harder problem. It just means we don't know, and we need to keep looking. Do you disagree?
  - lamontcg 4y ago
    They sterilized the market as a containment protocol for SARS-CoV-2, which eliminated the evidence. With SARS-1 the market was still fully operating when they went looking for the origins. Once the human pandemic kicks off and you find some civets or whatever with the virus, then how do you prove they had it before the humans unless you have lucky lab samples drawn from civets who were infected prior to Dec 2019? You'd need to do something like find civit-adapted SARS-CoV-2 which could be genetically dated to prior to Dec 2019 because there were simply too many mutations to have been backspill from the human pandemic. If the spread in civets started very shortly before the spread in humans then that would likely not be possible at this point. If you could find a virus in civets that was 5 years of genetic drift away from SARS-CoV-2 that would probably work, but that may never have existed. What remains is finding the persistent bat reservoir.
    - tripletao 4y ago
      A civet (assuming hypothetically that's the intermediate host for SARS-CoV-2) infected before Dec 2019 would provide strong genomic evidence of forward zoonosis. A civet infected afterward could still provide that evidence though, if it's by a zoonotic lineage distinguishable from the one that spilled over into humans (if such a lineage exists; you're of course correct it's not guaranteed to). For now that's all academic though, since we've found zero animals infected by any lineage of SARS-CoV-2, excluding animals that we're quite confident were infected directly or indirectly by humans, from the timing, circumstances, and genomic evidence. I don't think your scenario is impossible, and the traders themselves also had good incentive to hide or dispose of suspect animals before anyone could swab them. There's inherently no direct evidence for it, though. It seems like most arguments over the origin of SARS-CoV-2 eventually reduce to arguments over what the Chinese government has concealed, whether deliberately or accidentally as part of their containment protocol. That makes the argument hard to resolve, though there's still considerable unexplored evidence within reach of American or European subpoena, like a search through all available raw sequencer reads between September and December 2019 for contamination from SARS-CoV-2 or related viruses.

sudosysgen 4y ago

If SARS-1 was more infectious and less virulent you wouldn't see cases concentrated amongst traders, would you? If anything, since many of them already have some kind of immunity from previous infection, you would not expect them to even notice being sick before the virus already infected thousands.

tripletao 4y ago
I agree that finding the origin of a virus that's less deadly and faster-spreading (like SARS-CoV-2) is a harder problem. Nevertheless: 1. We quickly found pretty good evidence (infected civet cats and raccoon dogs, and infected human traders of those animals) that SARS-1 arose from natural zoonosis, within about a year of its emergence in humans. The later discovery of WIV-1 didn't add to this evidence. 2. We've found no such evidence for SARS-CoV-2. That doesn't mean SARS-CoV-2 definitely arose unnaturally--we've expended a lot more effort looking, but it really is a harder problem. It just means we don't know, and we need to keep looking. Do you disagree?
- lamontcg 4y ago
  They sterilized the market as a containment protocol for SARS-CoV-2, which eliminated the evidence. With SARS-1 the market was still fully operating when they went looking for the origins. Once the human pandemic kicks off and you find some civets or whatever with the virus, then how do you prove they had it before the humans unless you have lucky lab samples drawn from civets who were infected prior to Dec 2019? You'd need to do something like find civit-adapted SARS-CoV-2 which could be genetically dated to prior to Dec 2019 because there were simply too many mutations to have been backspill from the human pandemic. If the spread in civets started very shortly before the spread in humans then that would likely not be possible at this point. If you could find a virus in civets that was 5 years of genetic drift away from SARS-CoV-2 that would probably work, but that may never have existed. What remains is finding the persistent bat reservoir.
  - tripletao 4y ago
    A civet (assuming hypothetically that's the intermediate host for SARS-CoV-2) infected before Dec 2019 would provide strong genomic evidence of forward zoonosis. A civet infected afterward could still provide that evidence though, if it's by a zoonotic lineage distinguishable from the one that spilled over into humans (if such a lineage exists; you're of course correct it's not guaranteed to). For now that's all academic though, since we've found zero animals infected by any lineage of SARS-CoV-2, excluding animals that we're quite confident were infected directly or indirectly by humans, from the timing, circumstances, and genomic evidence. I don't think your scenario is impossible, and the traders themselves also had good incentive to hide or dispose of suspect animals before anyone could swab them. There's inherently no direct evidence for it, though. It seems like most arguments over the origin of SARS-CoV-2 eventually reduce to arguments over what the Chinese government has concealed, whether deliberately or accidentally as part of their containment protocol. That makes the argument hard to resolve, though there's still considerable unexplored evidence within reach of American or European subpoena, like a search through all available raw sequencer reads between September and December 2019 for contamination from SARS-CoV-2 or related viruses.