NS06 - Prions

Biomedical Sciences III

What does the term “prion” stand for?

Prion stands for proteinaceous infectious agent.

Do prions contain nucleic acid?

No, prions contain no nucleic acid.

What is the normal cellular form of the prion protein?

PrPC – a GPI-linked, membrane-bound protein that modulates membrane protein function in the brain.

What is the infectious form of the prion protein?

PrPSc – a protease-resistant, hydrophobic, fibril-forming protein that lacks nucleic acid.

How does PrPSc differ structurally from PrPC?

PrPSc has a beta-sheet structure, while PrPC has an alpha-helical structure.

What model explains prion proliferation?

The template-mediated protein refolding model.

How does PrPSc propagate?

It binds to PrPC, converting it into PrPSc, which then aggregates into amyloid fibrils.

What is the result of prion aggregation in the brain?

Formation of spongiform vacuoles, leading to neurodegeneration.

Do prions trigger an immune response?

No, prions cause no inflammation and no immune response.

What is the incubation period for prion diseases?

It can be very long, sometimes exceeding 30 years.

How are prions transmitted?

Through ingestion, injection, direct brain infection, inheritance, or sporadic mutation.

• Most commonly sporadic mutation

What tissues are high-risk for prion transmission?

CNS tissue, pituitary, and eye tissue (e.g., corneal transplants).

Are prions easily destroyed by standard sterilization?

No, they are extraordinarily resistant to inactivation.

What are CDC-recommended sterilization methods for prions?

1N NaOH or full-strength bleach for 1 hour, followed by autoclaving at 134°C for 60 minutes.

Are prions destroyed by UV light, alcohol, or formalin?

No, prions are not reliably destroyed by these methods.

What are the major human prion diseases?

Creutzfeldt-Jakob Disease (CJD), Variant CJD (vCJD), Fatal Familial Insomnia (FFI), Gerstmann-Sträussler-Scheinker (GSS), and Kuru.

What are the three modes of prion disease acquisition?

Sporadic (85–90%), Genetic (10–15%), and Acquired (1–3%).

What is the median age of death for classic CJD?

Around 68 years old.

What are the symptoms of CJD?

Dementia, behavioral changes, myoclonus, ataxia, blindness, and rapid progression to death.

What is the median duration of illness for CJD?

4–5 months after symptom onset.

How is CJD diagnosed definitively?

Post-mortem brain examination.

What is vCJD linked to?

Consumption of BSE-contaminated beef (Mad Cow Disease).

What is the median age of death for vCJD?

Around 28 years old.

How does vCJD differ from classic CJD?

Younger age, longer illness duration (14 months), psychiatric symptoms, and delayed neurological signs.

What is the incubation period for vCJD?

10–15 years.

Where were most vCJD cases reported?

United Kingdom.

What are the major animal prion diseases?

Scrapie (sheep/goats), Bovine Spongiform Encephalitis (BSE) (cattle), Chronic Wasting Disease (CWD) (deer/elk), and Kuru (humans via cannibalism).

What is Chronic Wasting Disease (CWD)?

A prion disease in deer, elk, moose, causing weight loss, stumbling, and neurologic symptoms.

Has CWD been reported in humans?

No confirmed cases, but animal studies suggest potential risk.

What is the infection rate of CWD in wild populations?

10–25%, up to 80% in captive herds.

Why are prions difficult to control microbiologically?

They are protease-resistant, lack nucleic acid, and do not elicit immune responses.

What precautions are taken in medical settings for prion exposure?

Use of disposable instruments, incineration, and rigorous sterilization protocols.