Prion disease (transmissible spongiform encephalopathy)

Pathophysiology and mechanism

Prion diseases arise when the normal host prion protein (commonly called PrP) adopts an aberrant, beta-rich conformation that is partly resistant to degradation. The abnormal form acts as a template and promotes conversion of native PrP into the same misfolded state, leading to accumulation of insoluble aggregates and progressive neuronal damage. This process is distinct from conditions caused directly by a mutant gene product, although some prion diseases are associated with inherited variants in the prion protein gene.

Key features include long incubation periods, regional vulnerability of the brain, formation of amyloid or non-amyloid aggregates, and a spectrum of so-called "strains" that differ in clinical and pathological patterns despite identical amino acid sequence. Species barriers and strain characteristics influence transmissibility between species and affect public health risk.

Clinical presentation and diagnosis

Most human prion diseases primarily affect the brain and nervous system. Common clinical features are rapidly progressive dementia, ataxia, behavioral or personality change, visual disturbances and involuntary jerks (myoclonus). Neuropathology typically shows neuronal loss, spongiform vacuolation and abnormal prion protein deposition.

Diagnosis is based on clinical evaluation supported by neuroimaging, electrophysiology and laboratory tests. Brain MRI can show characteristic signal changes, electroencephalography may show periodic complexes in some forms, and cerebrospinal fluid or nasal brushings can be tested for surrogate biomarkers and for misfolded prion protein using highly sensitive techniques such as seed amplification assays. Definitive diagnosis historically relies on neuropathological examination at biopsy or autopsy.

Forms, transmission and epidemiology

Human prion diseases include sporadic Creutzfeldt–Jakob disease (sCJD), inherited prion disorders linked to PRNP variants, iatrogenic cases from contaminated medical materials, and variant CJD associated with exposure to infected animal products. Animal prion diseases include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle and chronic wasting disease in cervids. Transmission can occur through contaminated tissues, surgical instruments, transplanted materials or dietary exposure under specific conditions.

• Incidence: Sporadic forms are rare but occur worldwide; sCJD is estimated to affect on the order of one case per million people each year in many regions.
• Iatrogenic risks have declined due to improved safeguards and screening.
• Public health responses focus on surveillance, safe handling of biological materials and measures to limit exposure to potentially contaminated animal products.

Treatment, decontamination and research

No proven curative therapy exists for most prion diseases; clinical management is supportive and palliative. Because prions lack conventional nucleic acids and are unusually resistant to routine sterilization, specialized decontamination protocols and instrument-handling policies are required to reduce transmission risk. Research continues on sensitive diagnostics, the molecular basis of strain diversity, host factors that influence susceptibility and potential therapeutic strategies aimed at stabilizing the normal conformation or enhancing clearance of abnormal protein.

Historical context and public health

The modern prion concept arose from efforts to explain diseases such as kuru and sheep scrapie and was advanced by experimental and theoretical work that emphasized a protein-only infectious agent. Outbreaks and iatrogenic cases in the 20th century led to regulatory changes in blood donation, tissue handling and agricultural practices. Ongoing surveillance and public health measures remain important to limit known routes of exposure and to detect emerging risks.

For introductory summaries and technical reviews, see general overviews on disease features, discussions of genetic influences, and resources addressing the molecular basis and clinical management of prion disorders. For background on the concept and biology of prions consult sources about prion biology and about how these agents differ from bacteria and other infectious organisms with conventional genomes or metabolism.