[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other viruses and prions](https://durgical.com/en/microbiology/groups/other-viruses-and-prions/) › Prions

[Microbiology](https://durgical.com/en/microbiology/) · [Other viruses and prions](https://durgical.com/en/microbiology/groups/other-viruses-and-prions/)

# Prions

- Virus
- Non-enveloped (naked)
- Exam priority: medium

Not viruses: misfolded proteins that bend normal ones out of shape and destroy the brain; they survive routine sterilisation.

Updated 2026-11-01

Also called: agents of the spongiform encephalopathies

## Key points

- Prions are NOT viruses: no nucleic acid and no envelope; they are misfolded protein.
- Rapidly progressive dementia with myoclonus: think Creutzfeldt-Jakob disease.
- Brain with vacuoles (spongiform) and no inflammation.
- They survive routine autoclaving and usual disinfectants: special protocol for neurosurgical instruments.
- In hospital, standard precautions are enough: not spread by casual contact.

## At a glance

**Shape**
Protein aggregates and fibrils

**Genome**
None: a prion has no nucleic acid, it is protein only (PrPSc)

**Envelope**
Non-enveloped (naked)

**Type**
Misfolded prion protein rich in beta sheets; not a virus

**Stain**
Immunohistochemistry for PrP in brain tissue

## Morphology

- Normal prion protein (PrPc) sits on the neuron membrane
- The abnormal form (PrPSc) has the same sequence but another shape and forces the normal one to change
- Forms aggregates resistant to proteases, heat and many disinfectants

## Transmission

- Sporadic, with no known cause: the commonest form of Creutzfeldt-Jakob disease (CJD)
- Inherited, through mutations in the PRNP gene
- Iatrogenic: dura mater grafts, corneal transplants, human-derived growth hormone and contaminated neurosurgical instruments
- Dietary: beef from cattle with bovine spongiform encephalopathy (variant CJD); kuru from ritual cannibalism in Papua New Guinea
- Not spread by casual contact

**Reservoir:** Humans themselves (sporadic and inherited cases); cattle in variant CJD

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Chain conversion of the normal protein into the abnormal one
- Neuron death and vacuoles in the brain (spongiform change), without inflammation
- No immune response: no fever, no CSF white cells and no useful antibodies

## Diseases it causes

- Sporadic, inherited, iatrogenic and variant Creutzfeldt-Jakob disease [Prion diseases (Creutzfeldt–Jakob) →](https://durgical.com/en/conditions/prion-diseases/)
- Kuru, fatal familial insomnia and Gerstmann-Sträussler-Scheinker syndrome [Prion diseases (Creutzfeldt–Jakob) →](https://durgical.com/en/conditions/prion-diseases/)

## Clinical picture

- Dementia that progresses very fast, over weeks or months
- Myoclonus (muscle jerks), ataxia and visual disturbances
- The variant affects young people, with early psychiatric symptoms and pain on touch
- Always fatal

## Diagnosis

- MRI: diffusion hyperintensity in cortex, caudate and putamen
- EEG: periodic sharp-wave complexes
- Cerebrospinal fluid: RT-QuIC and 14-3-3 protein
- Confirmation by examination of brain tissue

## Treatment

No treatment cures or slows the disease; care is supportive and palliative.

Drug class only; doses and regimens are set by the clinician from the current guideline.

## Prevention

- High-infectivity tissues are brain, spinal cord and eye
- Instruments that touch them need a special protocol (chemical treatment with sodium hydroxide or hypochlorite plus autoclaving) or are discarded and incinerated; routine sterilisation is not enough
- Control of bovine spongiform encephalopathy in the meat chain
- Deferral of at-risk blood and organ donors

## Memory aid

"The prion is a bad influence": one twisted protein talks its neighbours into twisting the same way, and an ordinary autoclave cannot straighten it.

## Test yourself

Think of the answer, then tap the question to see it.

## Why are prions not viruses?

They have no nucleic acid, capsid or envelope: they are proteins with an abnormal fold.

## Which clinical triad suggests Creutzfeldt-Jakob disease?

Very rapidly progressive dementia, myoclonus and typical MRI or EEG changes.

## Why do neurosurgical instruments used on a patient with CJD need a special protocol?

Because prions survive routine sterilisation; chemical treatment plus autoclaving is used, or disposable material is incinerated.

## Which isolation precautions does a hospitalised patient with CJD need?

Standard precautions only, because it does not spread by casual contact or by the respiratory route.

## Which exposure is linked to variant Creutzfeldt-Jakob disease?

Eating beef from cattle with bovine spongiform encephalopathy.

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## Related

- [Rabies virus](https://durgical.com/en/microbiology/rabies-virus/)
- [Measles virus](https://durgical.com/en/microbiology/measles-virus/)
- [JC polyomavirus](https://durgical.com/en/microbiology/jc-polyomavirus/)

## Related conditions

- [Prion diseases (Creutzfeldt–Jakob)](https://durgical.com/en/conditions/prion-diseases/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Other viruses and prions](https://durgical.com/en/microbiology/groups/other-viruses-and-prions/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [About Prion Diseases | Prions | CDC](https://www.cdc.gov/prions/about/index.html) (CDC, 2024); [Infection Control for CJD | Classic CJD | CDC](https://www.cdc.gov/creutzfeldt-jakob/hcp/infection-control/index.html) (CDC, 2024).

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Representative model, for educational purposes only.

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