How does nature deal with prion diseases?

[u/ProDidelphimorphiaXX]

Wasn’t sure what to flair.

Prion diseases are terrifying, the prions can trigger other proteins around it to misfold, and are absurdly hard to render inert even when exposed to prolonged high temperatures and powerful disinfectant agents. I also don’t know if they decay naturally in a decent span of time.

So… Why is it that they are so rare…? Nigh indestructible, highly infectious and can happen to any animal without necessarily needing to be transmitted from anywhere… Yet for the most part ecosystems around the world do not struggle with a pandemic of prions.

To me this implies there’s something inherent about natural environments that makes transmission unlikely, I don’t know if prion diseases are actually difficult to cross the species barrier, or maybe they do decay quite fast when the infected animal dies.

[u/EricTheNerd2]

There is a fundamental flaw with your assumptions: prions are not terribly infectious. Animals with prions die off pretty quickly and to catch the disease you must consume the misshapen protein directly. It isn't like Covid where someone coughs and spreads it.

And once the host dies, unless something consumes it pretty soon thereafter, the prions won't be spreading.

[u/The_Frostweaver → u/EricTheNerd2]

I thought prions could survive for a a long time?

[u/ElysiX → u/The_Frostweaver]

"A long time" is relative. Misfolded proteins are still proteins, and proteins rot.

[u/throwawaystedaccount → u/ElysiX]

But isn't there an entire ecosystem of insects, rodents and scavengers that eat carcasses?

With so many different species feasting on that prion infected body, one would assume it would spread somewhat?

EDIT: Other answers in this thread clarify this to an extent.

EDIT2: Thank you for all the answers!

[u/MsNyara → u/throwawaystedaccount]

Each animal order and clade uses different proteins, and uses them in different ways and extent. This generally means that you need the same specie of animal scavenging the dead animal fresh, and then when such a scavenger dies, it also needs to be eaten by a similar scavenger. Generally this chain does not repeat for long and the prion is dead.

It can also be transmitted by blood and fluids, but just if the protein is used in the tissues it is getting contact at. This will be extremely specific in nature and potentially wipe an animal's family or geographical limited group, or nothing happens (aside the source individual dies).

It would be a fairly common disease if it was not for the fact that such protein misfold already just happens once every a couple hundred million living beings every a dozen years or so, so it really does not have much chances to spread outside farming, among farm animals.

[u/CoffeeFox → u/MsNyara]

So, hypothetically, let's say there was a blanket ban on using slaughterhouse byproducts in cattle feed: would it follow that BSE/mad cow disease be expected to die off on its own?

[u/MsNyara → u/CoffeeFox]

Bingo. It would stop altogether. If we did not use water contaminated by poop bird to pluck off feathers then we would not need to cook poultry neither, among a few other things that we do or that happens exclusively due to industrial farming being the way it is, since our demand is higher compared than the arable land available per human, which is just a fifth part of an hectare, which is just enough for 10kg of meat per person per year, not 60kg, or 120kg like in the US.

So to produce that surplus of meat, practices like this must be done to optimize space use. Or we would reduce our demand for meat, or have 6 times less humans (worldwide), any works.

[u/LotusMoonGalaxy → u/throwawaystedaccount]

There was a paper published, I wanna say in the last 6 months, that found that cougars intestines were capable of destroying deer wasting disease prions. So in a "natural world", nature does have ways of preventing cross contamination in species. And that's just mammal to mammal predation. Insects and birds have different everything which again, would prevent cross species contamination. Part of the chronic wasting deer problem is that there isn't enough predation, enough food and overcrowding so deer are spreading it faster than prions usually spread.

[u/MATlad → u/LotusMoonGalaxy]

Looks like a few papers coming out of that research group!

https://scholar.google.com/scholar?q=cougar+intestine+chronic+wasting+disease

[u/throwtrollbait → u/ElysiX]

Nah bro. Prions are so resistant to this that they might as well be immune. They've found a few weird microbes that can break them down, kind of. They remain infective for at least several years in soil in natural conditions.

But these bastards are so terrifyingly stable that even burning them is tricky. Like, incineration needs to be north of 900C for an extended period of time. Aluminum, brass, and bronze all melt before prions stop being infectious prions.

[u/ElysiX → u/throwtrollbait]

Everything filters down one way or another, and oxygen is the death of all.

Trying to sterilise medical tools is not the same situation as a damp forest floor. Yes the soil will be contaminated, but not forever. Every time that something eats it, it will either be destroyed, made smaller, or kill what ate it and possibly multiply a bit. But the chance that that thing gets eaten by something up the food chain rather than down is small. So eventually it ends up destroyed or so deep in the soil that nothing can reach it and it eventually decomposes.

[u/throwtrollbait → u/ElysiX]

As I mentioned, in the case of CWD, prions are infectious for years in soil under natural conditions.

Sure, they will eventually decay, one way or another, but that might happen years after their host species has gone functionally extinct.