This episode concludes the virology section with an agent that defies traditional classification: the prion. Drawing from Murray’s Chapter 56, it explores infectious disease caused not by bacteria or viruses, but by misfolded protein.

Prions lack nucleic acid. Instead, a normal cellular protein (PrPᶜ) undergoes conformational change into a pathogenic isoform (PrPˢᶜ). This altered structure induces further misfolding in neighbouring proteins, creating a cascade of abnormal accumulation.

The result is spongiform degeneration of neural tissue, leading to rapidly progressive neurodegenerative disease. Conditions include:

* Creutzfeldt–Jakob disease (sporadic, familial, variant)

* Kuru

* Gerstmann–Sträussler–Scheinker syndrome

* Fatal familial insomnia

Prions are uniquely resistant to conventional sterilisation methods, requiring specialised decontamination protocols.

Conceptually, prion disease challenges central assumptions of microbiology - infection without genome, replication without nucleic acid synthesis. Clinically, diagnosis is difficult and treatment remains supportive.

Key Takeaways

* Prions are misfolded infectious proteins

* No nucleic acid is involved

* Disease involves progressive neurodegeneration

* Transmission may be sporadic, inherited, or acquired

* Standard sterilisation methods are insufficient

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