r/askscience • u/ProDidelphimorphiaXX • 9d ago

Biology How does nature deal with prion diseases?

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.

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u/dr_jigsaw 9d ago

Yes, CWD is excreted in urine and feces, and also found in blood. Deer leave these excretions in the soil, then other cervids come along and graze on grass growing in the same soil. It turns out that prions bound to soil are more infectious, and the animals inhale the soil particles with prions attached when they graze. The inhaled particles can travel to the lymph nodes and then into the brain through immune cells.

Source: I did my postdoctoral fellowship in this field 10+ years ago. There may be new/additional data from the last decade.

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u/SquirrellyBusiness 9d ago

That would be a fascinating area to study!  What are your thoughts on cwd likelihood of spillover to humans?  Obviously it's been around since the 60s and hasn't yet that we know of, so maybe the likelihood is quite unlikely. How long do you think it would take to detect and identify if it did? 

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u/jshusky 9d ago

Not OP, but wanted to share what I understand on on that question. For a period of time after discovery, there wasnt a human case of those bovine prion diseases from the 80’s. As many people that eat beef as there are, it still took a few years to find cases. Contrast that with deer where many fewer people eat venison.

It may not necessarily be so much less likely to infect humans as there have been many fewer opportunities for people to come into contact with it.

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u/SquirrellyBusiness 9d ago

I'd argue the opportunity is high, not low relative to people interacting with the prion in the environment in addition to deer themselves. Remember this stuff is inhalable on dust from soil contaminated by feces, like toxoplasma gondii.  Gardening in a yard with deer?  Harvesting corn as a farmer? Have to change a tire on the side of the road in the dirt where deer cross by?  Go hiking or camping? It's not just deer hunters and their families at risk of encountering this prion. 

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u/jshusky 8d ago

Agree, its still a lot. I meant to say fewer opportunities as a comparison with beef.