I’ve read of accounts of “Kuru” and from what I’ve read the diseases caused by prions generally have a long incubation period, and that it can take a very singular prion to cascade into a complete disease.
In: Biology
You *generally* don’t consume the nerve tissues of other humans. This does put a bit of a barrier into the usual way one can catch a case of neurodegenerative prions.
Then you pretty much already know. Prion diseases are barely contagious in terms of R0, the average number of people that an infected person goes on to infect (which needs to be at least >1 for the disease to keep spreading).
Prions are scary stuff. We know how to kill bacteria, and we’re starting to get a handle on viruses. But prions straight up aren’t alive in the first place -they’re literally just snippets of protein that are folded the wrong way- and that makes them much harder to destroy. Ordinary disinfection and even cooking don’t work on them.
However, not being alive has its disadvantages. Because prions aren’t alive, they can’t respond to stimuli, and because of that, they can’t adapt to changes in their environment: they are what they are, and they can’t become anything else. And that means prions can’t evolve new ways to spread. They live in brain tissue and act on brain tissue, and to date the only known way for them to spread is through contact with brain tissue (or with things that have been in contact with brain tissue; prions being hard to destroy give them an advantage here). It’s very hard to make an epidemic happen under those conditions.
Prion diseases just aren’t contagious enough to cause an epidemic/pandemic. Kuru originated in a group that practiced cannibalism, and it spreads through direct contact with brain tissue. It’s not like COVID, where you can get sick simply from being around an infected person. Unless you’re eating human brains on a regular basis, there’s basically no risk of you ever getting kuru.
Prions haven’t caused a human epidemic mainly because they don’t spread easily between people, have a long incubation period, and are quite rare. Unlike viruses, prions require direct contact with infected tissue for transmission, which is uncommon in most societies. The long incubation period means symptoms take years to show, reducing the risk of spread. Additionally, strict control measures, especially in food industries, have been implemented to prevent outbreaks, such as those seen with mad cow disease. So, despite their potential for harm, the unique characteristics of prions and our preventive efforts have kept large-scale outbreaks at bay.
Human prion diseases have three etiologies: sporadic, genetic, and acquired. Unlike scrapie in sheep and chronic wasting disease in deer, human prion diseases don’t appear to be spread environmentally – variant CJD from mad cows disease being the major exception. So human to human transmission is limited to a few select cases (kuru via burial cannabilism, and a few cases of vCJD spread via medical procedures). High risk surgical procedures (tonsillectomies and appendectomies in particular) have shifted to using disposable instruments to reduce this risk.
There is also a strong genetic component to prion disease resistance – heterozygosity (different amino acids) at codon 129 of the human prion protein gene (PRNP) is known to confer relative resistance to both sporadic and acquired prion diseases. In kuru, heterozygosity is associated with older patients and longer incubation times. All of those who developed vCJD were in the methionine homozygotic category (having the same methionine amino acid at codon 129). Variations in other codons are also protective against prion disease development. This was observed in Papua New Guinea where specific variants were protective against kuru. Statistical data suggests that ~50% of the human population fall into a category where a prion disease is unlikely to develop during their normal lifespan, and another ~25% only develop a prion disease with a late onset. That still leaves ~25% of the population at risk of rapid prion disease development, but this suggests that an epidemic is unlikely.
Because every instance of “Mad Cow” disease have been quickly curtailed. Entire herds where a single cow had it were killed off and not consumed
Most people don’t eat the brain or spine at all, especially Americans. Now that there has been a prominent scare the industry has taken precautions to minimize the risk of transmission. Prions can spontaneously form, it’s a bit like cancer but more rare. Things need to be very contagious in order to become plagues
I believe that the most common prion for humans is Crutchfield-Jacob’s Disease. IF a hospital allows a patient with CJD into an operating room, there’s a number of precautions taken, including sealing the room for a period of time after before cleaning.
One of my coworkers with housekeeping would assist family that ran a funeral home, and had a client who had passed with CJD, and they explained that out of precaution, their only option was straight to cremation with no visitation out of precaution.
While they can randomly form in anyone at any time, they usually don’t. They’re incredibly rare. And while it can be passed by consuming infected tissue, how often do you eat human nervous tissue? I have eat to do that, so my chances are really low.
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