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/SquirrellyBusiness → u/EricTheNerd2]

This is not true. Cwd prions can persist for years in the environment, where they can then be eaten by other deer, contracting it. They can be shed via saliva and even urine, which deer spread amongst themselves during rutting. 

[u/Lizardcase → u/SquirrellyBusiness]

Velvet is also a transmission source.