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
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.
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