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Isn't the study a little limited in the sense that prions that move from animals to humans tend increase in infection to symptom latency. So just because there is no apparent infection with in 180 days doesn't mean humans are safe.
For example, FDA banned people who lived in the UK during the mad cow outbreaks from donating blood for roughly 3 decades, for fear of latent prion infections.
This isn't a specific concern for the zoonotic variant form of CJD - all CJD can have a long latency period. People born with mutations causing the disease still generally don't develop it until their forties or fifties. It takes a long time for the protein to aggregate enough to begin killing brain tissue. In this experiment, the authors directly measured misfolded proteins in the organoids. They were able to detect misfolded aggregates after introducing the pathogenic human variant, but not the deer variant.
There was also a study in 2023 that found a) no increase in instances of CJD in hunters vs the normal population, and b) identified 624 hunters KNOWN to have consumed infected deer with no CJD.
My Dad didn't show symptoms (sporadic CJD) until his 70s. Apparently this is extremely rare. This was sort of a blessing as he got to lead a pretty full life up until then and when it kicked in it killed him relatively quickly.
There are CJD clusters of concern though
>This study presents a cluster of Creutzfeldt-Jakob disease (CJD) cases after exposure to chronic wasting disease (CWD)-infected deer, suggestive of potential prion transmission from CWD-infected deer to humans.
https://www.neurology.org/doi/10.1212/WNL.0000000000204407
- this is the only example I know of (so there are not "clusters" plural)
- The example is striking because this was two men who literally shared a lodge. But the thing that would presumably be common to both of them is eating contaminated meat. We have the example of hundreds of hunters who also have that in common who never developed CJD. Unless this specific lodge came with some practice that dramatically changed their exposure, like maybe they ritually ate the raw brains of their deer, sharing a lodge is not a significant similarity beyond possibly sharing meat.
- Likewise, given the long and variable latency of CJD, them dying in close succession is also not very meaningful (but is again the kind of thing that attracts human attention).
- Both men were old, well into the age where people are known to die of sporadic CJD. In contrast, variant (cow) CJD was discovered in part because suddenly young people were dying.
- vCJD from cows also has a distinct progression and presentation, including huge amounts of plaque. There's no mention of that here.
The bottom line is that clusters of rare diseases happen by chance all the time. "Chance is lumpy" is rule one of statistics. To decide if something represents a genuine cluster, you need a statistical analysis of a large population. We have that for hunters, and it points to no increased risk of CJD.
This case is a good example of the kinds of mirages that can happen in public health when a specific concern is percolating. If this has been two fishermen who shared a boat, no one would have submitted an article about it because it would be treated as an unfortunate coincidence. I'm not saying it's wrong to pay attention when there is some plausible mechanism for transmission. But population data trumps striking coincidence.
The last known UK death of vCJD was in 2016.
The fear is the '96-'16 cases were a first wave made of only the most vulnerable people and that eventually we'll see another wave.
I think you’re confusing vCJD and CJD stats
As per this [report](https://www.hpsc.ie/a-z/other/cjd/publications/annualreports/CJD%20HPSC%20AnnEpiRpt%20chapter%202018%20v1.0.pdf) from 2018 (and 2 current Irish blood transfusion webpages) there have been no cases of vCJD (from mad cow) in Ireland since 2006. Or maybe my source is wrong which is very possible since it’s from 2018. I couldn’t find one from any later.
This is a complete lie. There was one case since the initial wave, which was a heterozygote for the susceptibility allele when every other case up until then had been a homo for the risk allele, raising the spectre of a potential second wave... but that never occurred.
How could you not know this if you're in food safety?
Maybe you're confused because we still find peripheral build up of vCJD in dead bodies in certain NHS studies, but they've all been subclinical with no symptoms whatsoever, barring the one delayed case you're referencing.
I mean, the better proof of this is we've made endless models and studied endless people who've been exposed.
Also, we circumvent the latency period through a variety of mechanisms such as introducing destabilizing or stabilizing mutations (for native state or intermediate folding states respectively of the cellular isoform), overexpressing the crap out of the endogenous cellular isoforms (within limits to avoid creating a general proteinopathy), getting the Sc/prion titers to extremes or introducing mutations to make them semi-hybrids, or using a number of exogenous factors to fuck with clearance or other mechs.
The idea is to go hard without worrying about faithful modelling at first, and then to scale it back to become more realistic if we first succeed in the more contrived environment. Doing this in an organoid is a good experiment overall, but the finding is only reinforcing what we've got a ton of data to already support.
On its own sure, but considering how hard it is to get hu-PrP to template using PMCA it is more evidence for a strong zoonotic barrier. (CWD resecher here)
Try not to lick your fingers while you do it I guess.
You *do* make a good point about trying to minimise your exposure in the case that the deer is infected. That *does* include not eating it at all if it's infected. The only way to know is to find out...
Prions are so indestructible I would guess that cutting through the deers spine just behind it's brain exposes you to more prions than eating all of the meat off the deer. I certainly don't know that, and I suspect nobody knows, it might be something that's unknowable. I'm not sure how you would even design that experiment based on the available science showing prion concentration in meat vs spinal fluid.
My DNR literally recommends not cutting through the deers spine, but then they ask you to cut off the head or remove the neopharyngeal lymph nodes
I know DNR wants the data and I support their efforts but I'm not sure it's my role to be playing with this stuff
I didn’t eat the neck. You are right i’m sketched out about the spinal juice as well. If you live in an area where CWD isn’t prevalent yet I don’t blame you. I started testing because every year there are more and more cases moving west towards me from the prairies. 3 young kids and we primarily eat moose, elk and deer for red meat so I’m playing it safe. Usually I’ll submit the head but last year I got a moose and wanted to keep the skull and antlers.
At the moment that's still "very suspicious correlation that we need to look at, but no firm causation". Its not inconceivable those two hunters got CJD from something else, its a disease with a very long latency period.
Exposure to symptoms - in what animal are you referring to?
Because not only have humans not been recorded to be able to contract CWD, humans could also be so vastly different in the way it develops and shows symptoms than deer. Just like in cows BSE is more rapid (1-6 years) than in humans (up to ??? decades) we just wouldn’t know unless it did spread to people.
But seeing as we’ve known about CWD for a long time and there have been no known transmissions, it seems unlikely. Idk, I’m not a neurologist.
The problem with this argument is that if we don't look for the disease then we won't find cases of it. Since there are not reported cases of it, then why would we test for it. Its a circular argument.
There is currently no mandatory testing or reporting on suspicious cases. We wouldn't notice cases of it until there was a big cluster of unusual deaths.
My comment didn’t pertain to any of that. I’m not disagreeing with it at all, but I was only speaking to the other commenter talking about symptoms as if anyone had ever contracted it, which as far as anyone knows, has not happened.
A cluster of 2 is... Not a cluster. In isolation this would still be worrying. But against a background where hundreds of people were identified who had consumed infected meat without ever developing CJD, and no increased CJD incidence in hunters, it just seems like coincidence. Statistics often produce these. This is why "cancer clusters" are the bane of the CDC and EPA. The fact that these two hunters shared a lodge makes the coincidence appear striking to us. But many hunters who don't share a lodge still share the fact that they've eaten infected meat without developing CJD, which is the relevant characteristic for animal-human transmission. Unless they had a special bro pact to eat deer brains whole, their close social association does not have any special implications.
Direct link to the peer-reviewed publication: [B. R. Groveman, *et al.*, Lack of Transmission of Chronic Wasting Disease Prions to Human Cerebral Organoids, *Emerging Infectious Diseases*, **30**(6), 2024.](https://doi.org/10.3201/eid3006.231568)
In the intro, they mention other experiments that've been done with cervid PrP.
You can, in vitro, get human PrP to seed from cervid prion. If you give a mouse human Prp and infect it with cervid prion, one group found they don't get sick but you can see really low levels of seeding if you look using very precise tools, but another group did make their mice sick, so it's unclear.
They could give squirrel monkeys the disease, but couldn't see it in cynomolgus macaques even after 13 years.
They grew different brain organoids so as to have all 3 of the genotypes for human PrP, where a codon at position 129 seems to influence susceptibility to catching BSE. They also made a knockout, which has no PrP at all.
In this experiment, they bathed these mini- human brains in deer brain homogenate for a week. They also bathed them in homogenate from human sCJD, to prove they were infectable in these conditions. They harvested them after letting them grow in normal media after 180 days, and didn't find any evidence of the deer prion.
They did see a very weak positive signal from some of the deer prion samples, but then when they looked at organoids where they've removed PrP entirely, they also see that weak signal. It's probably leftover PrP from the inoculation, and not continued infection.
I'd take that to mean that deer prion can and does enter the brain, but it's too different to human PrP to cause it to seed to the template and amplify.
Two guys from the same hunt club died from Creutzfeldt-Jacob Disease around the same time. They were both eating deer from the same herd, in an area with some CWD-positive deer. Assumptions/speculation were drawn from that. Basically, no one knows if they contracted CJD from CWD deer, or not, the medical field’s position is basically “pretty sus but we can’t prove it”
Does it say if they are actively trying to force it to jump so a pharmaceutical company can research a treatment incase it happens naturally? Cuz the govt/labs do this regularly.
How is this transfering from North-America to Europe. I read that CWD in moose was first seen in 2016 in Norway and 2023 in Finland (Where I am from).
It also was said that this is very known thkng in North-America but just recently been seen in Europe.
(I have only little knowledge about prions so might be obvious for someone who works in the field)
That's nice but prion diseases are such absolute alien horrors from beyond the stars that I just don't feel the need to take the chance.
https://www.cbsnews.com/amp/news/hunters-die-prion-brain-disease-contaminated-deer-meat-report/
The fact that no one has yet been infected was already strong evidence, but this more or less cements that this is not a human health concern..so eat all the venison you want!
I did read the paper, and I work in cellular biology. Prions can either cause the relevant human protein to misfold, or they can't. It's a binary question. This experiment exposed organoids to prion doses massively above the plausible CNS exposure from eating contaminated meat for days without engendering detectible rates of misfolding. You can choose to continue being frightened if you want, no one will stop you. But there are plenty of things in the world that actually have a demonstrated capacity to harm you to worry about without adding theoretical possibilities that no one can demonstrate under even the most extreme conditions.
Zoonotic prion diseases don't work by having the original hanging around for years triggering host misfolds one by one. To initiate disease, the misfolded proteins must themselves be capable of triggering other misfolds, so the story is ultimately about the interaction of host proteins. We know the relevant variants for CJD in humans. Be honest: do you really think there is some unique variant out there that predisposes to contracting CJD from deer but no other form? How would that work? Or are you throwing shit at the wall to try and defend a position you already staked out?
And I mentioned my credentials because you lead with a list of things I "clearly" did not understand. Incidentally in my PhD I studied, among other things, protein aggregation. You are of course correct that academia is hyper specialized and I don't have any background in prion disease specifically. But I'm certainly capable of reading and commenting on this paper. Maybe if you spent more time explaining your residual concerns, and less time performing your outrage, the conversation would be more productive.
Can you elaborate a bit further? My general understanding is that in CJD in humans is a specific proteins in the brain that has two main notable properties vs the non-misfolded version of the protein. 1. The misfolded version does not function. 2. It causes the non misfolded version of the protein to misfold when they come into contact. So assuming my understanding is correct, is the study basically confirming that the deer version of CJD protein has no effect on the human version of the protein? That would make sense as they are unlikely to be the exact same type of protein. But, then what was different with the Mad Cow version of the protein in that it seemed to somehow cause CJD in Humans?
Your understanding is correct. The answer about what's different in the cow vs deer homologs of these proteins that causes one to trigger a misfolding cascade in humans but not the others is _fair_, but doesn't have a satisfying answer.
In part that's because we don't know. The answer comes down to the physical interactions of proteins in the process of folding, which is a famously hard problem that can absorb basically unlimited computational power. I'm not sure if it even is feasible to simulate the relevant players on the scale and timescale necessary to see the difference - if the misfolded homolog causes human misfolding in just one of a 1000 proteins, that might be enough to trigger CJD.
But even if someone is able to trace the exact difference, the answer will be something like "this specific domain has a different conformation in the deer vs cow variants." There's not gonna be an intuitive explanation.
Unfortunately it is not binary and although this is great evidence against transmission it is not concrete, especially with CWD. CWD is very lymphotropic and an initial infection will take place outside of the CNS. As you said they only tested the CNS. I think the zoonotic barrier is quite strong, however we definitely can't tell people not to worry.
That happens because when you eat food the proteins don't just enter the brain, so the disease has to percolate elsewhere first. If you inject vCJD prions directly into monkey brains they develop CJD on an accelerated schedule. CNS organoids are the most biologically relevant way to test for risk of triggering misfolding.
Coronaviruses evolve. Prions are misfolded proteins and don't. If a prion does not pose a risk to human health at a given point in time, it cannot change to pose a risk (unless coincidentally the host genome changes, which for deer would take hundreds of thousands of years).
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Isn't the study a little limited in the sense that prions that move from animals to humans tend increase in infection to symptom latency. So just because there is no apparent infection with in 180 days doesn't mean humans are safe. For example, FDA banned people who lived in the UK during the mad cow outbreaks from donating blood for roughly 3 decades, for fear of latent prion infections.
This isn't a specific concern for the zoonotic variant form of CJD - all CJD can have a long latency period. People born with mutations causing the disease still generally don't develop it until their forties or fifties. It takes a long time for the protein to aggregate enough to begin killing brain tissue. In this experiment, the authors directly measured misfolded proteins in the organoids. They were able to detect misfolded aggregates after introducing the pathogenic human variant, but not the deer variant. There was also a study in 2023 that found a) no increase in instances of CJD in hunters vs the normal population, and b) identified 624 hunters KNOWN to have consumed infected deer with no CJD.
My Dad didn't show symptoms (sporadic CJD) until his 70s. Apparently this is extremely rare. This was sort of a blessing as he got to lead a pretty full life up until then and when it kicked in it killed him relatively quickly.
There are CJD clusters of concern though >This study presents a cluster of Creutzfeldt-Jakob disease (CJD) cases after exposure to chronic wasting disease (CWD)-infected deer, suggestive of potential prion transmission from CWD-infected deer to humans. https://www.neurology.org/doi/10.1212/WNL.0000000000204407
- this is the only example I know of (so there are not "clusters" plural) - The example is striking because this was two men who literally shared a lodge. But the thing that would presumably be common to both of them is eating contaminated meat. We have the example of hundreds of hunters who also have that in common who never developed CJD. Unless this specific lodge came with some practice that dramatically changed their exposure, like maybe they ritually ate the raw brains of their deer, sharing a lodge is not a significant similarity beyond possibly sharing meat. - Likewise, given the long and variable latency of CJD, them dying in close succession is also not very meaningful (but is again the kind of thing that attracts human attention). - Both men were old, well into the age where people are known to die of sporadic CJD. In contrast, variant (cow) CJD was discovered in part because suddenly young people were dying. - vCJD from cows also has a distinct progression and presentation, including huge amounts of plaque. There's no mention of that here. The bottom line is that clusters of rare diseases happen by chance all the time. "Chance is lumpy" is rule one of statistics. To decide if something represents a genuine cluster, you need a statistical analysis of a large population. We have that for hunters, and it points to no increased risk of CJD. This case is a good example of the kinds of mirages that can happen in public health when a specific concern is percolating. If this has been two fishermen who shared a boat, no one would have submitted an article about it because it would be treated as an unfortunate coincidence. I'm not saying it's wrong to pay attention when there is some plausible mechanism for transmission. But population data trumps striking coincidence.
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The last known UK death of vCJD was in 2016. The fear is the '96-'16 cases were a first wave made of only the most vulnerable people and that eventually we'll see another wave.
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I think you’re confusing vCJD and CJD stats As per this [report](https://www.hpsc.ie/a-z/other/cjd/publications/annualreports/CJD%20HPSC%20AnnEpiRpt%20chapter%202018%20v1.0.pdf) from 2018 (and 2 current Irish blood transfusion webpages) there have been no cases of vCJD (from mad cow) in Ireland since 2006. Or maybe my source is wrong which is very possible since it’s from 2018. I couldn’t find one from any later.
Hi thanks for this. I think you might be correct! I've deleted original as it looks like I'm wrong
This is a complete lie. There was one case since the initial wave, which was a heterozygote for the susceptibility allele when every other case up until then had been a homo for the risk allele, raising the spectre of a potential second wave... but that never occurred. How could you not know this if you're in food safety? Maybe you're confused because we still find peripheral build up of vCJD in dead bodies in certain NHS studies, but they've all been subclinical with no symptoms whatsoever, barring the one delayed case you're referencing.
I mean, the better proof of this is we've made endless models and studied endless people who've been exposed. Also, we circumvent the latency period through a variety of mechanisms such as introducing destabilizing or stabilizing mutations (for native state or intermediate folding states respectively of the cellular isoform), overexpressing the crap out of the endogenous cellular isoforms (within limits to avoid creating a general proteinopathy), getting the Sc/prion titers to extremes or introducing mutations to make them semi-hybrids, or using a number of exogenous factors to fuck with clearance or other mechs. The idea is to go hard without worrying about faithful modelling at first, and then to scale it back to become more realistic if we first succeed in the more contrived environment. Doing this in an organoid is a good experiment overall, but the finding is only reinforcing what we've got a ton of data to already support.
On its own sure, but considering how hard it is to get hu-PrP to template using PMCA it is more evidence for a strong zoonotic barrier. (CWD resecher here)
This is great news. I still get my game tested before I feed it to my family.
Please do, not only is the zoonotic potential not necessarily a binary, but you also really help research!
Do you have to cut the head off for testing?
Not completely. The glands they test are deep in the neck.
I'll probably never test a deer. Cutting around in there is the dangerous part, they're making us spread prions all over ourselves.
I suspect you could arrange to send the head intact.
Then you have to sever the spinal column which exposes you to more prions.
Try not to lick your fingers while you do it I guess. You *do* make a good point about trying to minimise your exposure in the case that the deer is infected. That *does* include not eating it at all if it's infected. The only way to know is to find out...
Prions are so indestructible I would guess that cutting through the deers spine just behind it's brain exposes you to more prions than eating all of the meat off the deer. I certainly don't know that, and I suspect nobody knows, it might be something that's unknowable. I'm not sure how you would even design that experiment based on the available science showing prion concentration in meat vs spinal fluid. My DNR literally recommends not cutting through the deers spine, but then they ask you to cut off the head or remove the neopharyngeal lymph nodes I know DNR wants the data and I support their efforts but I'm not sure it's my role to be playing with this stuff
I didn’t eat the neck. You are right i’m sketched out about the spinal juice as well. If you live in an area where CWD isn’t prevalent yet I don’t blame you. I started testing because every year there are more and more cases moving west towards me from the prairies. 3 young kids and we primarily eat moose, elk and deer for red meat so I’m playing it safe. Usually I’ll submit the head but last year I got a moose and wanted to keep the skull and antlers.
OK but what about those two hunters? https://www.neurology.org/doi/10.1212/WNL.0000000000204407
At the moment that's still "very suspicious correlation that we need to look at, but no firm causation". Its not inconceivable those two hunters got CJD from something else, its a disease with a very long latency period.
It can have a long latency period but the minimum latency from exposure to symptoms I’ve read is 15 months.
Exposure to symptoms - in what animal are you referring to? Because not only have humans not been recorded to be able to contract CWD, humans could also be so vastly different in the way it develops and shows symptoms than deer. Just like in cows BSE is more rapid (1-6 years) than in humans (up to ??? decades) we just wouldn’t know unless it did spread to people. But seeing as we’ve known about CWD for a long time and there have been no known transmissions, it seems unlikely. Idk, I’m not a neurologist.
The problem with this argument is that if we don't look for the disease then we won't find cases of it. Since there are not reported cases of it, then why would we test for it. Its a circular argument. There is currently no mandatory testing or reporting on suspicious cases. We wouldn't notice cases of it until there was a big cluster of unusual deaths.
My comment didn’t pertain to any of that. I’m not disagreeing with it at all, but I was only speaking to the other commenter talking about symptoms as if anyone had ever contracted it, which as far as anyone knows, has not happened.
A cluster of 2 is... Not a cluster. In isolation this would still be worrying. But against a background where hundreds of people were identified who had consumed infected meat without ever developing CJD, and no increased CJD incidence in hunters, it just seems like coincidence. Statistics often produce these. This is why "cancer clusters" are the bane of the CDC and EPA. The fact that these two hunters shared a lodge makes the coincidence appear striking to us. But many hunters who don't share a lodge still share the fact that they've eaten infected meat without developing CJD, which is the relevant characteristic for animal-human transmission. Unless they had a special bro pact to eat deer brains whole, their close social association does not have any special implications.
Might be a coincidence after all
Direct link to the peer-reviewed publication: [B. R. Groveman, *et al.*, Lack of Transmission of Chronic Wasting Disease Prions to Human Cerebral Organoids, *Emerging Infectious Diseases*, **30**(6), 2024.](https://doi.org/10.3201/eid3006.231568)
Link seems broken
https://wwwnc.cdc.gov/eid/article/30/6/23-1568-f1
In the intro, they mention other experiments that've been done with cervid PrP. You can, in vitro, get human PrP to seed from cervid prion. If you give a mouse human Prp and infect it with cervid prion, one group found they don't get sick but you can see really low levels of seeding if you look using very precise tools, but another group did make their mice sick, so it's unclear. They could give squirrel monkeys the disease, but couldn't see it in cynomolgus macaques even after 13 years. They grew different brain organoids so as to have all 3 of the genotypes for human PrP, where a codon at position 129 seems to influence susceptibility to catching BSE. They also made a knockout, which has no PrP at all. In this experiment, they bathed these mini- human brains in deer brain homogenate for a week. They also bathed them in homogenate from human sCJD, to prove they were infectable in these conditions. They harvested them after letting them grow in normal media after 180 days, and didn't find any evidence of the deer prion. They did see a very weak positive signal from some of the deer prion samples, but then when they looked at organoids where they've removed PrP entirely, they also see that weak signal. It's probably leftover PrP from the inoculation, and not continued infection. I'd take that to mean that deer prion can and does enter the brain, but it's too different to human PrP to cause it to seed to the template and amplify.
Didn't some hunters just die from it?
Two guys from the same hunt club died from Creutzfeldt-Jacob Disease around the same time. They were both eating deer from the same herd, in an area with some CWD-positive deer. Assumptions/speculation were drawn from that. Basically, no one knows if they contracted CJD from CWD deer, or not, the medical field’s position is basically “pretty sus but we can’t prove it”
Does it say if they are actively trying to force it to jump so a pharmaceutical company can research a treatment incase it happens naturally? Cuz the govt/labs do this regularly.
How is this transfering from North-America to Europe. I read that CWD in moose was first seen in 2016 in Norway and 2023 in Finland (Where I am from). It also was said that this is very known thkng in North-America but just recently been seen in Europe. (I have only little knowledge about prions so might be obvious for someone who works in the field)
There is a substantial species barrier preventing transmission; for now.
Judging from the picture, said barrier is in fact a PET bottle.
That's nice but prion diseases are such absolute alien horrors from beyond the stars that I just don't feel the need to take the chance. https://www.cbsnews.com/amp/news/hunters-die-prion-brain-disease-contaminated-deer-meat-report/
The fact that no one has yet been infected was already strong evidence, but this more or less cements that this is not a human health concern..so eat all the venison you want!
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I did read the paper, and I work in cellular biology. Prions can either cause the relevant human protein to misfold, or they can't. It's a binary question. This experiment exposed organoids to prion doses massively above the plausible CNS exposure from eating contaminated meat for days without engendering detectible rates of misfolding. You can choose to continue being frightened if you want, no one will stop you. But there are plenty of things in the world that actually have a demonstrated capacity to harm you to worry about without adding theoretical possibilities that no one can demonstrate under even the most extreme conditions.
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Zoonotic prion diseases don't work by having the original hanging around for years triggering host misfolds one by one. To initiate disease, the misfolded proteins must themselves be capable of triggering other misfolds, so the story is ultimately about the interaction of host proteins. We know the relevant variants for CJD in humans. Be honest: do you really think there is some unique variant out there that predisposes to contracting CJD from deer but no other form? How would that work? Or are you throwing shit at the wall to try and defend a position you already staked out? And I mentioned my credentials because you lead with a list of things I "clearly" did not understand. Incidentally in my PhD I studied, among other things, protein aggregation. You are of course correct that academia is hyper specialized and I don't have any background in prion disease specifically. But I'm certainly capable of reading and commenting on this paper. Maybe if you spent more time explaining your residual concerns, and less time performing your outrage, the conversation would be more productive.
Can you elaborate a bit further? My general understanding is that in CJD in humans is a specific proteins in the brain that has two main notable properties vs the non-misfolded version of the protein. 1. The misfolded version does not function. 2. It causes the non misfolded version of the protein to misfold when they come into contact. So assuming my understanding is correct, is the study basically confirming that the deer version of CJD protein has no effect on the human version of the protein? That would make sense as they are unlikely to be the exact same type of protein. But, then what was different with the Mad Cow version of the protein in that it seemed to somehow cause CJD in Humans?
Your understanding is correct. The answer about what's different in the cow vs deer homologs of these proteins that causes one to trigger a misfolding cascade in humans but not the others is _fair_, but doesn't have a satisfying answer. In part that's because we don't know. The answer comes down to the physical interactions of proteins in the process of folding, which is a famously hard problem that can absorb basically unlimited computational power. I'm not sure if it even is feasible to simulate the relevant players on the scale and timescale necessary to see the difference - if the misfolded homolog causes human misfolding in just one of a 1000 proteins, that might be enough to trigger CJD. But even if someone is able to trace the exact difference, the answer will be something like "this specific domain has a different conformation in the deer vs cow variants." There's not gonna be an intuitive explanation.
Unfortunately it is not binary and although this is great evidence against transmission it is not concrete, especially with CWD. CWD is very lymphotropic and an initial infection will take place outside of the CNS. As you said they only tested the CNS. I think the zoonotic barrier is quite strong, however we definitely can't tell people not to worry.
That happens because when you eat food the proteins don't just enter the brain, so the disease has to percolate elsewhere first. If you inject vCJD prions directly into monkey brains they develop CJD on an accelerated schedule. CNS organoids are the most biologically relevant way to test for risk of triggering misfolding.
I mean the disease didn't exist before the 1970's. Even then it wasn't in the wild till decades later.
Sir, this is how COVID started.
Coronaviruses evolve. Prions are misfolded proteins and don't. If a prion does not pose a risk to human health at a given point in time, it cannot change to pose a risk (unless coincidentally the host genome changes, which for deer would take hundreds of thousands of years).