What is a Prion?

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The term "prion" is derived from proteinacious infectious particles and refers to the pathogen that causes transmissible spongiform encephalopathies (TSEs).

Abnormal (misfolded) prions - Medical microbiology animations


This small infectious particle is a disease-causing form of a protein called cellular prion protein (PrPc). PrPc is mainly found on the surface of cells in the central nervous system (CNS), but it is also located in other bodily tissues. Although the specific role of PrPc is not clear, studies suggest that this protein plays a protective role in cells and helps them respond to oxygen deficiency.  

A prion is composed of an abnormally folded protein that causes progressive neurodegenerative conditions, with two of the most notable being Bovine spongiform encephalopathy (BSE or mad cow disease) seen in cattle and livestock and Creutzfeldt-Jakob disease (CJD) seen in humans.

These misfolded proteins do not multiply in the host organism that they infect. Instead, they affect the brain structure by acting as a template, inducing proteins with normal folding to convert to the abnormal prion form.

These newly formed misfolded proteins, in turn, act as further templates for the conversion of more normal proteins, leading to an exponential accumulation of prions in the tissue of the CNS. These abnormally folded proteins form plaques which are thought to cause "entanglement" of neurofibrils and interfere with synapse function.

Image Credit: Crystal Eye Studio / Shutterstock.com

The nerve cells are eventually damaged and lost, which causes tiny vacuoles to form in the brain. These give the brain a sponge-like appearance under the microscope, hence the term spongiform disease arose.

This leads to brain damage and the symptoms of prion disease, which include impaired brain function, changes in personality, memory, and behavior, intellectual decline, and movement abnormalities, particularly ataxia. These symptoms usually develop during adulthood and worsen over time, eventually causing death within several years or even a few months.

Prion features

Prions are smaller than viruses and can only be seen through an electron microscope when they have aggregated and formed a cluster. Prions are also unique in that they do not contain nucleic acid, unlike bacteria, fungi, viruses, and other pathogens.

Prions are therefore resistant to procedures that destroy pathogens by breaking down nucleic acid. Furthermore, because these particles are an abnormal version of a normal protein that is already coded for in the body, they do not trigger a host immune response, as other pathogens do.

The normal prion protein is thought to be made up of flexible coils referred to as alpha helices; however, in the abnormally folded form, these helices are stretched out into densely packed structures called beta-sheets. Cellular enzymes referred to as proteases can break down the normal protein; however, prion proteins are unfortunately resistant to this and subsequently accumulate in the brain tissue as they replicate.

Prion-like behavior can also be seen in certain types of fungi. These fungal prions have been studied extensively to provide clues as to how prions affect mammals, although fungal prions are not harmful to their host.

Prion discovery

In the late 1960s, research showed that the agent that causes sheep TSE or scrapie was highly resistant to deactivation by ultraviolet and ionizing radiation, both of which are therapies that would usually destroy any pathogens that contained nucleic acid. However, the nature of these particles was still unclear, which led scientists to make various suggestions including proteins, membrane fragments, small DNA viruses, and polysaccharides.

Some researchers decided that whatever the nature of the agent was, it did not depend on nucleic acid to reproduce. In 1982, Stanley B. Prusiner from the University of California in San Francisco published an article in Science describing the process of purifying the scrapie-causing agent and he described a protein.

Prusiner wrote in the article, "Because the novel properties of the scrapie agent distinguishes it from viruses, plasmids, and viroids, a new term "prion" was proposed to denote a small proteinaceous infectious particle that is resistant to inactivation by most procedures that modify nucleic acids." Prusiner’s discovery led to him being awarded the Nobel Prize in 1997.


  1. https://www.cdc.gov/
  2. www.nhs.uk/.../Introduction.aspx
  3. https://www.uclh.nhs.uk/
  4. http://ghr.nlm.nih.gov/condition/prion-disease
  5. http://www.bseinfo.org/priondefinition.aspx

Further Reading

Last Updated: Oct 29, 2022

Sally Robertson

Written by

Sally Robertson

Sally first developed an interest in medical communications when she took on the role of Journal Development Editor for BioMed Central (BMC), after having graduated with a degree in biomedical science from Greenwich University.


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  1. jerry Rogers jerry Rogers United States says:

    Where are prions found ? in the soil ? if so can you test for prions?

  2. Lyle Zoerman Lyle Zoerman United States says:

    My concern is in creating GMO foods that may have the same result as prions. It took decades to discover, and it still takes maybe 2 decades to diagnose after initial infection. If a GMO creates a prion or prionlike folded protien, it could decimate a population before discovery.

    • Bill Board Bill Board United States says:

      The modifications inherent within GMOs are highly specific and specialized within their targeted function, specifically limited to areas of plant growth cycles, and resistance to specific organisms, ie, molds or pests.  The ingestion of these foods are broken down within human digestion, such that their constituent molecular bases are synthesized the same as any food. Food not absorbed is simply excreted.  The possibility of say... oncogene synthesis, or horizontal gene transfer and the genesis of prions from plants modified isn't plausible as there is no chain mechanism to enable this.

  3. Jim Strange Jim Strange Australia says:

    Is it possible for earth to be seeded with prions from comet and cosmic dust. I.e. can they survive interstellar or solar radiation?

  4. Mohamed Pasha Mohamed Pasha Saudi Arabia says:

    why prions attack only nervous tissue

  5. Candi Carter Candi Carter United States says:

    Does anyone know if Prions are in any way related to Morgellons? I ask because I helix shaped blue fiber came out of my sons cheek, after a bath and rub with tea tree and coconut oil. Oh, and we've hall had viral like symptoms since October of Last year (2015).

  6. Kenneth Letterman Kenneth Letterman Brazil says:

    Prions do not, I presume, survive at high temperatures or in acidic environments, or do they? They must be specific to nervous tissue like enzymes and the chaperonin proteins. Is there a relation between prions and enzyme creation, activation, or denaturation? What of all the proteins related to enzyme complexes? Pro-enzymes, pre-enzymes...

  7. Kenneth Letterman Kenneth Letterman Brazil says:

    Chaperonin proteins are involved in promoting the correct folding of proteins so that aggregation does not occur. What if the chaperonins themselves were somehow destroyed but functioned well enough to induce misfolding?

  8. Evans Muthomi Evans Muthomi Kenya says:

    your articles always help me with my studies

  9. Michael Pereira Michael Pereira United States says:

    A prion is a small virus, a harmful enzyme, composed of just s few amino acids, like substance P.

  10. Husain Janu Husain Janu Islamic Republic of Pakistan says:

    Any one give answer prions are rna virus or dna viras

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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