Submitted by matrixadmin- t3_zy43wl in askscience
Wouldn't bats have the virus which was then presumably transmitted to humans? Then how come we haven't found natural reservoirs of the virus in bats or other animals yet?
Maybe the reservoirs disappear or are simply too small or isolated to find?
Many coronaviruses that are extremely closely related to SARS-CoV-2 have been found in bats - both before the COVID outbreak, and after.
Coronaviruses in bats don’t tend to exist as clear, unambiguous, stable populations. There’s extensive recombination and rapid evolution, and the many small semi-distinct populations of bats means that there are many small, transient populations of coronaviruses in these populations.
On top of that, it’s probable that SARS-CoV-2 isn’t strictly a bat virus - coronaviruses recombine rapidly and readily, and recombination with a non-bat coronavirus is likely for both SARS and SARS-CoV-2 (pangolins, in the case of SARS-CoV-2). So there’s no reason to believe that SARS-CoV-2 exactly ever circulated in bats.
So the notion that it should be easy, or even possible, to identify exactly the same virus in bats over many years is obviously mistaken. Nevertheless, many very close relatives of SARS-CoV-2 have been found in Asian bats, including several that seem to be very capable of replicating in humans and that share the receptor specificity of SARS-CoV-2.
> We found that the receptor-binding domains of these viruses differ from that of SARS-CoV-2 by only one or two residues at the interface with ACE2, bind more efficiently to the hACE2 protein than that of the SARS-CoV-2 strain isolated in Wuhan from early human cases, and mediate hACE2-dependent entry and replication in human cells, which is inhibited by antibodies that neutralize SARS-CoV-2. … Our findings therefore indicate that bat-borne SARS-CoV-2-like viruses that are potentially infectious for humans circulate in Rhinolophus spp. in the Indochinese peninsula.
-Bat coronaviruses related to SARS-CoV-2 and infectious for human cells
It’s important to remember that there are vast numbers of bats, and that they have been very superficially sampled. In spite of this, it’s been very easy to find these close hits, showing that these very dangerous, human-preadapted viruses are very common in bats.
Virologists have been warning about this for decades, specifically calling out that the next pandemic was likely to arise from bat coronaviruses. It shouldn’t be surprising that the prediction actually came true.
Thanks for the explanation. Since you’re a virologist what steps should we take to prevent another coronavirus pandemic?
That's a different question that should be asked separately, it's a public health question, not a virology question, and it shouldn't be limited to coronaviruses.
Ok
Bat origin is an unproven theory. One possibility is that the virus originated in bats and was passed to another animal where it evolved to become SARS-CoV-2.
Bats have really interesting immune systems which are really good at combating viruses. For this reason they may make a good candidate for viruses to evolve and jump to another species.
And since bats are so good at fighting off viruses the original virus would no longer exist.
Technical sidenote: keep in mind that COVID-19 is the disease associated with the virus which is called severe acute respiratory syndrome coronavirus-2 or SARS-Cov-2.
Edit: added "severe acute respiratory syndrome"
I would edit that to remove "coronavirus-2 or" -- it's not nearly the second coronavirus ever detected and I don't think it's ever been referred to by that label (other than in your comment). Wikipedia says "Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2)" -- you can't just drop the first 4 words.
Thanks, didn't mean to omit. Added.
It's very tricky to find a natural reservoir of a coronavirus like this. You might want to compare with SARS 1, where a very similar virus was found in palm civets being sold for food at the time of the outbreak. But that was a combination of luck and extensive testing. The civets are likely to have been an intermediate step, hosting the virus after it left bats and before it entered humans. But remember, viruses are constantly mutating, so the virus in the civets wouldn't necessarily be the same as the virus in the bats or the people.
Anyway, why can't we do this with SARS 2? Because when the outbreak happened, China locked down their wet markets and killed most of the animals, which means there was very little sampling done. This probably means we'll never know exactly what path the virus took to get from bats to people.
>killed most of the animals, which means there was very little sampling done
Is that a normal procedure? I would imagine that getting as much samples as possible would be a priority, especially since wuhan has a lot of research facilities.
There is no normal procedure for the outbreak of a pandemic like Covid-19. Everything was kind of going crazy.
If you want to take the more charitable view, you could say the Chinese government was desperate to stop the virus from spreading and put a much higher priority on wiping out potential sources of infection (eg, the animals) and preventing spread (by locking down) than in getting researchers moving around to sample those animals before they were killed.
If you were going to be less charitable, you might say the Chinese government maybe didn't want conclusive proof to be found that it's mess of wet markets had, predictably, caused another zoonotic disease outbreak and was quite happy to see all the potential evidence killed off before it could be sampled....especially by any independent outside researchers.
One thing that's worth noting is that while it's academically interesting to know the exact path and intermediate hosts that covid took to get into people, it's actually not that important from a public health perspective. We know the broad strokes pretty well even without having all the intermediate steps perfectly filled in.
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Several studies over the past two years have found deer to be a covid reservoir
https://scholar.google.com/scholar?q=covid+deer+reservoir
There are plain english explainers on the NPR website but not sure if non-study links are allowed in this sub
I’ve heard about a lot of animals becoming covid reservoirs like minks but was referring to the reservoir or animal that it came from.
Note that that is not the question that you actually asked--in fact, it is much different, because even if "bats have the virus" that wouldn't tell us which bats were the original source ... surely the answer you're looking for as to "which animal" isn't simply "bats".
Precision is important in science. Speaking of which: COVID-19 is a disease. You presumably want to know about the origin of the virus, SARS-CoV-2. This distinction is particularly relevant to your question because an animal might well harbor the virus without having any disease symptoms, or it could have disease symptoms different from those that present in humans.
As for the origin: note that it took 14 years from the first case of SARS-1 until the originating bat population was stumbled upon. For numerous reasons, such a discovery may well never happen for SARS-CoV-2. (One of those possible reasons is something I dare not mention here, but you're likely to run across it if you google "Alina Chan".)
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BackStrict977 t1_j23vhg6 wrote
Some perspective you might need here:
1- It's not feasible to screen all the virus present in a bat population. If you tried you'd likely find many new virus no one ever described and still only know a small subset of the viral population within the bat population.
2- Vírus won't stay still and remain the same. The sars-cov-2 we have today is different from the one we first described and that would also apply to it's ancestors. Even if we find this ancestor it wouldn't be a 100% match. Parasites adapt to their hosts and sars-cov-2 jumped the species barrier at least once and maybe twice. The simple fact that a virus is in different hosts put new selective pressures on them.
3- We have find similar virus in the wild. The RaTG13 has around 96% identity to sars-cov-2 genome. This is not enough to say that one came from the other but shows that we can find some similar things if we look closely to betacoronavirus populations in bats.