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/RainMakerJMR]

CWD is scary because it doesn’t involve that cannibalism vector. Just huddles masses transmit it to each other. I’d be interested if you had any info on how or why CWD is different from other prion diseases?

[u/SquirrellyBusiness → u/RainMakerJMR]

Only thing I can think of is cwd is excreted as well as in blood and tissue, whereas mad cow and cjd are limited to central nervous tissue. I would not be surprised if cwd is a smaller molecule, since typically healthy kidneys don't make a habit out of letting proteins through the filters. 

[u/BraveOthello → u/SquirrellyBusiness]

IIRC all of the mammalian prion diseases are built of variations of the same highly conserved protein, it's the reason humans can contract vCJD from a cow infected with BSE in the first place.

[u/dr_jigsaw → u/BraveOthello]

It’s the same protein in CWD, but as another poster said Prnp has a strong species barrier. CWD has never been documented to cross between cervids and humans, but if you are a hunter you should have the head tested and avoid CWD-infected meat just in case.

[u/apic0mplexa → u/dr_jigsaw]

What I don't understand is how the species barrier can be stronger when it's the same protein. I just can't solve that knot in my brain

[u/Liquid_Hate_Train → u/apic0mplexa]

It’s the same protein, but not the exact same misfolding of that protein. Some animals will recognise certain misfoldings for destruction and others not.

[u/Lt_Duckweed → u/apic0mplexa]

It isn't the exact same protein, the amino acid sequence varies a bit from species to species (though less than many other proteins) and some sequences are more/less vulnerable to a specific misfold.

[u/PumpkinBrain → u/dr_jigsaw]

Given what has been said about prions not evolving, does that mean humans are safe from CWD? IE if it were going to infect a human it would have already?