Prions

Waverly S.
Aug 8, 2025
8 min read

Olin, North Carolina

Have you ever heard of a disease that is caused by a nonliving pathogen, contains no genetic material, and is impossible to survive? Prion diseases, also known as transmissible spongiform encephalopathies (TSEs), which have been documented as far back as 1732, occur when a misfolded protein interacts with regularly shaped proteins, leading other

proteins to misfold and clump together–a process that causes brain damage. Different prion diseases within the same species are caused by differences in the specific way that prion proteins misfold. At this point in time, sixteen prion diseases have been discovered, nine of which affect humans, with the other seven affecting other mammals.

Normal vs. diseased prion structures: green and red coils. Normal shows amino acids in sheet form, diseased shows amino acids in form of beta helix. — An illustration of a typical prion protein compared to a misfolded prion protein.

Prion is short for “proteinaceous infectious particle,” a name created by Stanley Prusiner, whose discovery of prions in 1982 won him a Nobel Prize in 1997. Prion proteins, named after the disease, are actually harmless microscopic proteins that are normally found in the brains of most healthy mammals and are not dangerous unless they misfold. Not much is known about what function prion proteins naturally serve, but their exclusive presence in the mammalian brain means that prion diseases only occur in mammals. Also, since prions are located in the brain, an organ vital for survival, a scientist is unable to confirm that a person has a prion disease until after their death, as attempting to harvest prions from the brain of an infected host would be very dangerous, and could lead to death or further brain damage. For this reason, prion diseases are primarily diagnosed based on possible instances of exposure, family history, and symptoms.

A black-and-white image of elongated structures composed of prions, called prion rods. — A collection of prion rods, structures composed of misfolded prion proteins, within biological tissue.

What makes prion diseases so deadly? The answer lies in the nature of the disease. Most diseases are caused by living organisms, like bacteria and fungi. A key characteristic of a living organism is its ability to die. If a biotic pathogen is deprived of the necessities needed to survive, it will no longer be able to carry out cellular processes, and it will cease to live, which usually eliminates the danger of a disease. However, in the case of a prion disease, the disease is not a living organism, but a molecule, which cannot be killed and requires very little to remain intact inside of the body. The immune system does not recognize the protein, which is created by the human body, as a threat, and does nothing to attack it, and there is no vaccine that can train the immune system to attack a prion. Of

course, there are experimental technologies being developed to destroy dangerous proteins like prions, but, as of today, the only reliable methods to kill prions are heating them to very high temperatures or exposing them to sodium hypochlorite, or bleach. These methods effectively destroy prions, but they still have one major issue: prions tend to reside within the nervous tissue of a living organism. This drawback prevents scientists from destroying prions without killing their mammalian hosts, making a prion disease impossible to cure.

Another very dangerous feature of a prion is its long incubation period. Some prion diseases have been documented to reside in hosts for decades before causing symptoms. Often, by the time a person shows signs of having a prion disease, like difficulty moving and memory loss, their death is very near, usually only months away. Concerningly, in the case of chronic wasting disease (CWD), one of the most contagious prion diseases, the pathogens can also reside in the environment for extended periods of time. Chronic wasting disease is distinct from most other prion diseases in that it can be spread through bodily fluids, including urine, saliva, feces, and blood, as the misfolded proteins are present in these substances. If an infected organism leaves prions in the environment, other creatures that interact with this habitat are at risk of developing the illness. An animal can be asymptomatic for over a year after acquiring CWD, making it difficult for authorities to identify a diseased animal before it is able to spread prions throughout its habitat. CWD is not known to affect humans, but the disease has spread to multiple continents, and many scientists fear the effects that it will cause if authorities cannot keep it from getting worse.

Microscopic view of pink brain tissue with spongiform appearance, showing porous lesions throughout. — The brain tissue of an individual with a prion disease, full of lesions resembling the texture of a sponge.

What, exactly, does a prion disease do to an infected organism? As mentioned in the introduction, another name for a prion disease is a transmissible spongiform encephalopathy (TSE). The reason that a prion disease is called “spongiform” is because the disease creates microscopic holes in the brain tissue of its host, causing the brain of an affected individual to develop a sponge-like appearance. These holes can cause various neurological symptoms, including difficulty moving, memory loss, hallucinations, and personality changes, which tend to rapidly progress after their initial onset. Once a person is diagnosed with a TSE, treatment is focused around symptom management and end-of-life care. There are three ways to categorize prion diseases: sporadic, hereditary (genetic), and acquired.

A prion disease is considered sporadic when a person develops the disease with no clear cause or trigger. In a sporadic prion disease, some of the prion proteins in an individual’s brain suddenly misfold, leading other prion proteins to do the same. Sporadic prion diseases tend to manifest in older individuals, and Creutzfeldt-Jakob disease, the most common TSE in humans, is sporadic in the majority of cases.

A hereditary, or genetic, prion disease occurs when the phenomenon of prion proteins misfolding is the result of a genetic mutation passed down from an individual’s parents. The gene that codes for prion proteins is known as the PRNP gene, and there are more than fifty mutations of this gene that are known to cause prion disease. Unfortunately, many of these mutations are autosomal dominant, meaning that if just one parent has it, the offspring will have a fifty percent chance of inheriting the mutated gene. Many rare TSEs are common in certain families. The gene for fatal familial insomnia, a prion disease, has only been documented in twenty-eight families around the world, and as of 2003, there were only around thirty families known to carry the gene for Gerstmann-Sträussler-Scheinker syndrome, although these figures have varied depending on the study. If a person develops a prion disease as a result of a sporadic genetic mutation, they will likely not pass it down to their offspring, as a sporadic mutation to nervous cells will not affect an organism’s gametes.

Finally, a prion disease is considered acquired when a patient develops a TSE as a result of coming into contact with infected tissue. The most common ways that a person might come into contact with infected tissue are through eating infected meat or undergoing a procedure that uses infected equipment or tissues, although experiments have shown that prions can also be spread through the air in the form of aerosols. Some of the most well-known prion diseases are acquired, such as bovine spongiform encephalopathy, or mad cow disease, a TSE that affects cows and was eventually proved to cause illness in humans.

Graph of Kuru deaths from 1957 to 2011. Red line shows total and under-20 deaths, blue line for males. Deaths decrease over time. — A graph showing the number of deaths caused by kuru from 1957 to 2011.

While scientists do not know for certain, many believe that BSE first started after cows were fed the remains of sheep that had scrapie, another prion disease. Cows with BSE were then consumed by humans, leading to the development of variant Creutzfeldt-Jakob disease, yet another prion disease, which killed hundreds of people. Another well-known acquired prion disease is kuru, which was endemic amongst the Fore people of New Guinea in the 1950s and 1960s. This disease ultimately killed around twenty-five percent of the female population during this time period, and was spread through the ritual consumption of human brain tissue during funerals. Upon learning about this disease, the government of New Guinea discouraged cannibalistic practices among the Fore people. These efforts drastically reduced the number of cases, with the last documented case of kuru in 2009.

Overall, prion diseases are some of the most unique diseases that scientists have ever discovered. The idea of a transmissible disease that contains no genetic material is so novel that some people still debate the true nature of prions to this day. The invariably fatal nature of TSEs is certainly tragic, but we can apply the lessons that we learn from outbreaks to improve medical safety and do our best to prevent more from occurring.

Works Cited

Ashe, K. H., & Aguzzi, A. (2013). Prions, prionoids and pathogenic proteins in Alzheimer disease. In Prion (Vol. 7, Issue 1, pp. 55–59). Prion. https://doi.org/10.4161/pri.23061

CDC. (2024a). About Prion Diseases. In Prion Diseases. https://www.cdc.gov/prions/about/index.html

CDC. (2024b). About Chronic Wasting Disease (CWD). In Chronic Wasting Disease. https://www.cdc.gov/chronic-wasting/about/index.html

Creutzfeldt-Jakob disease: Rare cause of dementia-Creutzfeldt-Jakob disease - Symptoms & causes. (n.d.). In Mayo Clinic. Retrieved March 9, 2025, from https://www.mayoclinic.org/diseases-conditions/creutzfeldt-jakob-disease/symptoms-causes/syc-20371226

Household Bleach Inactivates Chronic Wasting Disease Prions. (2019). In National Institutes of Health (NIH). https://www.nih.gov/news-events/news-releases/household-bleach-inactivates-chronic-wasting-disease-prions

Priola, S. A. (2018). Cell biology of prion infection. In Handbook of Clinical Neurology (pp. 45–68). Elsevier. https://doi.org/10.1016/b978-0-444-63945-5.00003-9

Prion Disease. (2024). In Cleveland Clinic. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/prion-disease

Prion Disease Fact Sheet. (2013). Pennsylvania Department of Health. https://www.pa.gov/content/dam/copapwp-pagov/en/health/documents/topics/documents/diseases-and-conditions/Prion%20Disease%20.pdf

Prion Diseases. (n.d.). In Memory and Aging Center. Retrieved March 24, 2025, from https://memory.ucsf.edu/dementia/rapidly-progressive-dementias/prion-diseases

Prion Diseases. (2015). In www.canada.ca. Government of Canada. https://www.canada.ca/en/public-health/services/diseases/prion-diseases.html

Prion Diseases. (2024). In NIAID: National Institute of Allergy and Infectious Diseases. https://www.niaid.nih.gov/diseases-conditions/prion-diseases

Prion Diseases. (2025). https://www.hopkinsmedicine.org/health/conditions-and-diseases/prion-diseases

Prusiner, S. B. (1998). Prions. In Proceedings of the National Academy of Sciences (Vol. 95, Issue 23, pp. 13363–13383). Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.95.23.13363

Stanley B. Prusiner. (n.d.). In Facts. Retrieved March 24, 2025, from https://www.nobelprize.org/prizes/medicine/1997/prusiner/facts/

Transmissible Spongiform Encephalopathies. (n.d.). National Institute of Neurological Disorders and Stroke. Retrieved March 25, 2025, from https://www.ninds.nih.gov/health-information/disorders/transmissible-spongiform-encephalopathies#toc-types-of-tses

What are Prions? (n.d.). Government of Virginia. Retrieved March 25, 2025, from https://dwr.virginia.gov/wildlife/diseases/cwd/what-are-prions

Zabel, M. D., & Reid, C. (2015). A brief history of prions. In Pathogens and disease (Vol. 73, Issue 9, pp. ftv087–ftv087). Pathogens and disease. https://doi.org/10.1093/femspd/ftv087

CDC. (2024). Clinical Overview of Variant Creutzfeldt-Jakob Disease. In Variant Creutzfeldt-Jakob Disease (vCJD). https://www.cdc.gov/variant-creutzfeldt-jakob/hcp/clinical-overview/index.html

Graph showing the total number of deaths from kuru from 1957, when investigations started, till 2011. (n.d.). ResearchGate. Retrieved April 16, 2025, from https://www.researchgate.net/figure/Graph-showing-the-total-number-of-deaths-from-kuru-from-1957-when-investigations_fig5_312403979from Royal Society Open Science

Haybaeck, J., Heikenwalder, M., Klevenz, B., Schwarz, P., Margalith, I., Bridel, C., Mertz, K., Zirdum, E., Petsch, B., Fuchs, T. J., Stitz, L., & Aguzzi, A. (2011). Aerosols transmit prions to immunocompetent and immunodeficient mice. In PLoS pathogens (Vol. 7, Issue 1, pp. e1001257–e1001257). PLoS pathogens. https://doi.org/10.1371/journal.ppat.1001257

Kuru: Causes, Symptoms and Diagnosis. (2012). In Healthline. https://www.healthline.com/health/kuru

Lai, E. (2003a). Prion Diseases. In Office Practice of Neurology (pp. 512–514). Elsevier. https://doi.org/10.1016/b0-44-306557-8/50081-2

Lai, E. (2003b). Prion Diseases. In Office Practice of Neurology (pp. 512–514). Elsevier. https://doi.org/10.1016/b0-44-306557-8/50081-2

Mathews, J. D. (2008). Review. The changing face of kuru: a personal perspective. In Philosophical transactions of the Royal Society of London. Series B, Biological sciences (Vol. 363, Issue 1510, pp. 3679–3684). Philosophical transactions of the Royal Society of London. Series B, Biological sciences. https://doi.org/10.1098/rstb.2008.0085

Lambert, Z. J., Greenlee, J. J., Cassmann, E. D., & M Heather West Greenlee. (2021). Differential Accumulation of Misfolded Prion Strains in Natural Hosts of Prion Diseases. In Viruses (Vol. 13, Issue 12, p. 2453). Viruses. https://doi.org/10.3390/v13122453

Imran, M., & Mahmood, S. (2011). An overview of human prion diseases. In Virology journal (Vol. 8, pp. 559–559). Virology journal. https://doi.org/10.1186/1743-422X-8-559

Normal and Abnormal Form Of Prion Protein Normal Prion Protein Has Amino Acids in Alpha. (n.d.). Retrieved April 20, 2025, from https://www.researchgate.net/figure/Normal-and-abnormal-form-of-prion-protein-Normal-prion-protein-has-amino-acids-in-alpha_fig1_326330981

Detecting Human Prion Disease. (2015). In National Institutes of Health (NIH). https://www.nih.gov/news-events/nih-research-matters/detecting-human-prion-disease