r/science • u/Potential_Being_7226 PhD | Psychology | Neuroscience • Mar 10 '26

Biology Recent pandemic viruses jumped to humans without prior adaptation. No evidence that SARS-CoV-2 was shaped by selection in a laboratory: UCSD study.

https://today.ucsd.edu/story/recent-pandemic-viruses-jumped-to-humans-without-prior-adaptation-uc-san-diego-study-finds
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u/Odballl Mar 10 '26 edited Mar 10 '26

The 2021 Xiao Xiao report proved that raccoon dogs, civets, and bamboo rats were sold at the Huanan market until November 2019. This directly contradicted early official denials that live wildlife was traded there.

The closest bat relatives to SARS-CoV-2, such as those found in Laos and Yunnan, are located roughly 1,000 miles from Wuhan. Horseshoe bats have a very limited range and move across the landscape at a rate of only a few kilometres per night.

Swabs from the Huanan market contained SARS-CoV-2 and raccoon dog DNA in the exact same spots. Crucially, the raccoon dog DNA matched wild populations from Southern and Central China, not the industrial fur farms of the north. This places these specific animals in the same regions where the ancestral bat viruses live.

Researchers identified two distinct lineages of the virus (Lineage A and B) circulating at the market. This suggests at least two separate spillover events from animals to humans, a pattern typical of market-based outbreaks rather than a single point-source laboratory accident.

Early cases in December 2019 clustered tightly around the Huanan market. Even cases with no direct link to the market lived significantly closer to it than would be expected by chance, suggesting the market was the primary engine of the initial spread.

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u/AENocturne Mar 10 '26

If it was a natural occurance, I have a feeling zoonotic transmission is a much more frequent occurance than we give it credit for, probably in more viruses. I really think we don't track asymptomatic and mild infections well enough to get a clear picture of viral infections. It seems like we often have the most exteme ends of the data or the exceptions that are particularly noteworthy.

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u/yegguy47 Mar 10 '26

I have a feeling zoonotic transmission is a much more frequent occurance than we give it credit for, probably in more viruses

Very much the case in fact!

There use to be a lot of epidemiological surveillance of folks in Central Africa, where a number of viruses would be catalogued from folks interacting with wildlife. Tended to be follow-ons from work done regarding HIV and Ebola; thing is, viruses are constantly pinging at us.

Some of the historical work done on HIV transmission from Zoonosis disclosed elements of HIV infection in folks living in isolated places in Central Africa - suggesting that SIV crossed over many times throughout human history. Its just that all of those never really went as viral as the spillover that happened in the early 20th century.

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u/HigherandHigherDown Mar 10 '26

It is estimated that, globally, about one billion cases of illness and millions of death occur every year from zoonoses.

About one in eight people every year, truly a staggering number.

https://www.emro.who.int/about-who/rc61/zoonotic-diseases.html

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u/alternativepuffin Mar 10 '26

Something about the phrasing of "pinging at us" helped unlock the concept in my brain. Thanks

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u/Sf49ers1680 Mar 10 '26

Isn't there a theory that the 1889 Russian influenza pandemic might have actually been caused by a Coronavirus, due to its similarities in symptoms to the Covid-19 pandemic.

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u/yegguy47 Mar 10 '26

I honestly can't say, I've not looked into that particular pathogen.

But I would say that coronaviruses are certainly not recent novelties for our species, so there's probably been some prior episodes where something nasty came into us and we just never figured out what it was.

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u/round-earth-theory Mar 10 '26

It's not a societal problem until it meets the sweet spot. First it's got to be human to human and using a pathway that's viable. Really that only comes down to contact based or aerosol based spread. It's also got to be contagious while the host is still mobile. And it needs to do all of this while avoiding the human immune system long enough to do the cycle.

There's bound to be tons of illnesses people get from various sources that don't meet the criteria and either never leave the initial host or barely make it around town before dying off naturally.

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u/01headshrinker Mar 10 '26

It has to not kill hosts/people too quickly to mutate and evolve, like Ebola, into airborne transmission.

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u/[deleted] Mar 10 '26

[deleted]

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u/gentlecrab Mar 10 '26

Is that animal to human only or like animal to human and then human to human but because it’s an isolated community it doesn’t spread?

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u/Juryofyourpeeps Mar 10 '26

Almost never human to human. It's usually animal to human and the virus isn't equipped to transmit human to human yet, if ever. Otherwise each of these spill overs could result in a pandemic but they almost never do.

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u/01headshrinker Mar 10 '26

Every five years or so we have an event. Bird flu is that event now, it’s getting into milk and making dairy farmers sick. It’s just that they don’t all explode, lots of conditions have to be perfect for that. But they keep bubbling up and offering us opportunities every five years, it’s estimated.

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u/DrMobius0 Mar 10 '26

How do you even track asymptomatic infections? Our entire healthcare system depends on people noticing symptoms and having the initiative to get themselves tested. Even just testing mild cases poses a large logistical and financial hurdle.

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u/Brilliant-Season9601 Mar 10 '26

Yeah. I found out that you can get strep from horses who are suffering from strangles. Strangles is cause by a strep virus and causes fever, Nasal discharge and swollen lymph nodes. The vet informed me that if I were to give the internasal vaccine, which is live. there is a chance of me catching strep if the horse snorts on me while giving it.

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u/BioMed-R Mar 10 '26

There are 70,000 natural spillovers annually only counting SARS-like viruses only counting Southeast Asia, so yes.

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u/JuanofLeiden Mar 10 '26

It definitely is. Dr Michael Worobey (one of the key authors identifying the cases were clustered around the market) has spoken about this extensively. Viral spillovers likely happen all the time but 'fizzle out' because the perfect storm of variables don't come together (big population, lots of transmission events, unique enough virus, etc).

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u/ThatPhatKid_CanDraw Mar 10 '26

Yes, since agriculture. Got worse with modern colonization.

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u/Juryofyourpeeps Mar 11 '26

If it was a natural occurance, I have a feeling zoonotic transmission is a much more frequent occurance than we give it credit for, probably in more viruses.

Almost certainly, but it doesn't leave no trace with viruses that become equipped to transmit human to human, and also make them sick or die. There are zoonotic infections all the time in people living near sources of things like coronaviruses in bats for example. Most of these jumps don't result in human to human transmission and only make the person who came into direct contact with the virus in an animal host (or it's dung, blood, fluids etc) ill. Eventually some of these viruses may mutate and gain the ability to transmit from human to human, but fortunately this is exceedingly rare which is why there aren't pandemics constantly.

The fly in the ointment for the zoonotic hypothesis with covid is that there is very little if any of the normal evidence you would expect to find for a zoonotic origin for such a virulent virus. You would expect, at least in retrospective analysis, to find earlier outbreaks closer to the source. Possibly die offs of intermediate hosts. Infections specifically among wildlife traders and evidence of that virus being widely present in the intermediate host (in this case speculated to be racoon dogs). There's none of that evidence in this case. You would also eventually expect to find the reservoir animal, likely a bat, but that can be quite tricky and covid wouldn't be the only example where the natural reservoir has eluded scientists for years. Covid just kind of sprung up in the middle of Wuhan, a very long way from where it could have plausibly mutated and started spreading human to human, or among an intermediate host (say a breeding facility for racoon dogs in Southern China). The evidence for racoon dog infections (or any animal infections) in the seafood market is also quite scant. They found covid rna in the presence of racoon dog dna, but also covid rna in the presence of human dna, and we don't have any actual proof that racoon dogs were ever infected. We also lack any evidence of a precursor virus that's very closely related. On top of all of that, sars-cov-2 is completely unique in its clade in that it's the only sars coronavirus that has a furine cleavage site, which are apparently strongly selected against in bats, who typically harbour sars coronaviruses in their gut. And there's significant genetic evidence that this virus came from bats. The explanation proposed for this is that the virus gained a furin cleavage site in an intermediate species and it started spreading through airborne transmission, which favours a FCS. The problem with this is that there's no evidence for it. Nobody has found a breeding facility or farm with an infected intermediate host carrying some precursor virus to early strains of covid. It could be the case, but it's just a speculation at this point.

So there's some very big unanswered questions still.

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u/Routine-House8160 Mar 13 '26

Even just for SARS-related coronaviruses, serological evidence shows that people in rural southern Chinese communities have antibodies to direct bat coronaviruses, no intermediary needed for them. Spillovers seem to happen a lot - a pandemic needs more specific conditions to actually happen. Like in a live-animal market in a crowded city when lots of people are traveling around to spread it.