Prion Disease

• Prion diseases are also knowns as transmissible spongiform encephalopathies (TSEs).
• They are a group of fatal neurodegenerative diseases which occur in a number of species, including man.
  • For example:
    • Bovine spongiform encephalopathy (BSE) in cattle
    • Scrapie in sheep
    • Chronic wasting disease in elk
    • Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker disease (GSS), fatal familial insomnia (FFI) and kuru in man
• TSEs have a long incubation period, making them difficult to diagnose.

Aetiology

• The aetiology of prion diseases is still highly controversial.
  • However, an abnormal isoform of the host-encoded prion protein (PrP) is seen in the brains of affected animals.
    • The normal host PrP changes its structure into the disease-associated form PrPSc.
  • The abnormal proteint (PrPSc) accumulates as amyloid fibrils in nervous tissue.
• The agent appears to be highly resistant.

Pathology

Gross

• Prion diseases cause NO GROSS LESIONS.

Histological

• TSEs typically cause what is known as the "microscopic triad":
  1. Spongiform change.
     • Vacuolation of neurons.
     • Particularly in nuclei.
  2. Astrogliosis
  3. Amyloid plaques
     • These are not always seen.