The most well-known legend surrounding prions is that they are a "curse from god for eating one's kind" or "god's ban on genes," but scientific advancements have shown that this may not be true.
In the 18th century, scrapie was discovered in Germany; the disease caused some sheep to exhibit maniacal behaviors, such as desperately rubbing back against surrounding objects until they finally starved themselves to death. What’s worse, the symptoms are spreading.
In the 1950s, in Papua New Guinea, a disease called kuru was found in the Formosa tribe. The patients appeared to have involuntary movement, ataxia, muscle stiffness, and other neurological disease symptoms. A ritual persisted in the Formosa tribe where relatives shared the brain tissue of the dead at their funerals, and researchers gradually discovered that kuru disease was primarily spread through the consumption of the neural tissue of the deceased. American scientists Daniel Culhope and Stanley Brown were awarded the 1976 Nobel Prize in Physiology or Medicine for their contributions to Prion's Disease, particularly for their research on kuru, and their experiments demonstrated that microorganisms had nothing to do with kuru.
The first cases of mad cow disease, which manifested itself as a neurological disorder similar to kuru, appeared in the United Kingdom in the late 1900s. The disease soon ravaged cattle, which were then massively culled and thrown into high-temperature incinerators, still, proved to be of little help with controlling the pandemic. Shortly afterward, many people in the UK experienced symptoms similar to the mad cows and died in convulsions. The common feature of these patients was that they had consumed beef from diseased cattle, and autopsies revealed that the brains of these dead people had become riddled with holes. With the UK being an exporter of beef, the disease of unknown origin quickly spread internationally and aroused much panic.
In 1982, American neuroscientist Stanley extracted a new pathogen from the brains of sheep suffering from scrapie—not a virus or a bacterium, but a protein molecule with no DNA or RNA—and named it a proteinaceous infectious particle. Prion was translated as "protein virus" in Chinese—where the term "virus" indicates infectiousness only—and has been used ever since. Because of their inability to replicate themselves, prions are currently not considered to be a form of life by mainstream academia.
But how can proteins cause diseases? Proteins that perform biological functions have a precise, restricted spatial conformation, and a prion is a misfolded protein. PrPSc interacts with PrPc (normal protein) and induces a change in spatial conformation by converting PrPc into PrPSc, which is the same as an autocatalytic enzyme. This chain reaction continues, like the development of a pyramid scheme, constantly developing downlines. A large number of normal PrPc proteins are converted, while the misfolded PrPSc aggregates form amyloid
deposits, destroying the normal function of the tissue, and ultimately resulting in neuronal death. With the neuronal disruption, the PrPSc will be absorbed by the surrounding neurons, and eventually, a large area of neuron death, forming a "spongy brain" phenomenon. The phenomenon of a "spongy brain" resembles a form of cancer at the protein level. Later studies have found similar protein-related mechanisms behind many neurodegenerative diseases, including mad cow disease, Creutzfeldt-Jakob disease, lethal familial insomnia, and Pattinson's disease.
How can prions be just proteins and have such infectious properties? Thanks to human interventions: during the 20th century, Britain made feeding supplements out of inedible parts of the cows and sheep, their brain marrow, bones, and entrails, and this type of man-made cannibalism ultimately led to the fall of the British pastures. It is not accurate to say that prions are the "ban from God against cannibalism," however, since individuals who ate the tissues of a cow that carried mad cow disease ended up infected—clearly not a case of cannibalism—but the pandemic brought about by prions poses substantial concerns for us.
References
Baiardi, Simone, et al. “Recent Advances in the Histo-Molecular Pathology of Human Prion Disease.” Brain Pathology (Zurich, Switzerland), vol. 29, no. 2, Mar. 2019, pp. 278–300. PubMed, https://doi.org/10.1111/bpa.12695.
Piñar-Morales, Raquel, et al. “Human Prion Diseases: An Overview.” Medicina Clinica, vol. 160, no. 12, June 2023, pp. 554–60. PubMed, https://doi.org/10.1016/j.medcli.2023.03.001.
---. “Human Prion Diseases: An Overview.” Medicina Clinica, vol. 160, no. 12, June 2023, pp. 554–60. PubMed, https://doi.org/10.1016/j.medcli.2023.03.001.
Shim, Kyu Hwan, et al. “Prion Therapeutics: Lessons from the Past.” Prion, vol. 16, no. 1, Dec. 2022, pp. 265–94. PubMed, https://doi.org/10.1080/19336896.2022.2153551.
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