Prions

Question 1

Prion diseases list

Answer 1

1. Kuru
2. Creutzfeldt-Jakob disease (CJD),
3. variant CJD (vCJD)
4. Gerstmann-Sträussler-Scheinker syndrome (GSS)
5. fatal familial insomnia (FFI)
6. variably protease-sensitive prionopathy (VPSPr)

Question 2

Prion pathogenesis

Answer 2

Neuro degenerative disorder

Prion protein — The normal (cellular) prion protein, PrPC, is a membrane-bound glycophosphatidylinositol-anchored protein found on both neuronal and nonneuronal cells in normal human brains.

Function - unclear. ?copper homeostasis.

Conversion of PrPC to PrPSc — The abnormal prion protein, PrPSc (so-designated after scrapie), is a conformational isomer of PrPC. PrPSc exists primarily as a beta-pleated sheet resulting from an as yet uncharacterized conformational alteration.

It is hypothesized that the initiating PrPSc molecule is derived from an exogenous source in acquired prion diseases (ie, iatrogenic CJD [iCJD], variant CJD [vCJD], and kuru), while mutations are invariably detected within the gene encoding PrP in familial forms.

Neurotoxicity- PrPSc appears to be neurotoxic, as accumulation of this protein or fragments of it in neurons leads to apoptosis and cell death.

Question 3

Prion diagnostics

Answer 3

1. Immunoblotting – Western blot analysis following proteinase K digestion is commonly used to detect disease-causing prion protein (PrPSc) in brain tissue
2. Real-time quaking-induced conversion – A similar assay, called real-time quaking-induced conversion (RT-QuIC), uses shaking instead of sonication to amplify minute levels of PrP by inducing pathologic seeding activity
3. Protein misfolding cyclic amplification

Question 4

vCJD

Answer 4

Acquisition of BSE by consumption of infected meat/ transfusion of blood from infected individuals (only vCJD).

232 cases worldwide - most from UK.

Incubation - very long and so asymptomatic for long time.

Mean age of onset - 29 compared to much later in sCJD.

Clinical - depression, sensory symptoms, cerebellar ataxia, myoclonus, dementia

Diagnostics: MR, CSF 14-3-3 protein, CSF real-time quaking-induced conversion (RT-QuIC)

Tonsillar tissue PrPSc detected on Western blot.

No treatment- ?Pentosan polysulfate (low-molecular weight heparinoid) case reports of prolonging life

Question 5

Kuru

Answer 5

Prototype human prion disease

Endemic in Papua New Guinea among the Fore linguistic group

transmitted from person to person by ritual cannibalism

Incubation - up to 50 years

Clinical - Tremors (Kuru = shivering), sedentary stage, Dementia, Frontal release signs, Death

Question 6

Prion/TSE Lab containment

Answer 6

Transport: Cat B UN3373

High risk tissues include brain, spinal cord, dura mater, posterior eye, pituitary, cranial nerves and ganglia.
- CL3

Medium risk tissues include spinal ganglia and olfactory epithelium, and in the case of VCJD: tonsil, spleen, appendix, thymus and gut associated lymphoid tissues - CL3

Low risk tissues include all others, most notably any patient-derived fluids like CSF, blood, urine, saliva - General Protective measures only.

For asymptomatic “at-risk” patients - general protective measures.

Cleaning and decontamination: As many of the standard methods of decontamination cannot ensure complete inactivation of prions and/or proteopathic seeds, the emphasis must be on prevention of spillages, single use equipment and the removal of the agent by specific cleaning protocols.

Spillages or contamination with low risk human biofluids can follow standard local procedures.

WHO recommended methods for prion destruction are exposure to a hypochlorite solution containing a final concentration of >20,000 ppm free chlorine or 1M NaOH for 1 hour at room temperature.

If this is not possible, alternatives:

Autoclave at ≥134oC for ≥20 minutes

Exposure to high concentrations of ionic detergents in aqueous solution at elevated temperature, eg >2% w/v SDS at >45°C

Exposure to strong chaotropes such as guanidine hydrochloride (>5M) or guanidine isothiocyanate (>3M).

Treatment with high concentrations of broad specificity alkaline proteases, eg proteinase K at >1mg/ml.

Question 7

Iatrogenic CJD

Answer 7

Administration of hormones prepared from human pituitary glands and dura mater preparations, and one case has been reported associated with a corneal graft

vCJD - one case blood transfusion.
Preventive methods employed:
1. Leucodepletion of blood products
2. Import of FFP & cryoprecipitate from US
3. People who underwent transfusion after 1980 are excluded from donations

Question 8

CJD/TSE IPC in hospital & OT

Answer 8

NO isolation needed

Standard precautions for low risk tissue handling including blood and CSF

Spillages cleaned using standard methods except in medium/high risk tissue - sodium hypochlorite 10,000 ppm.

Clinical waste incinerated

Bed linen washed & dried as per usual

Sharp injury HCW - bleed and wash wound/ irrigate eye or mouth. Report and monitor - no intervention.

Theatre measures:
1. Use theatre for procedures
2. Last case
3. Minimum number of staff
4. Disposables encouraged

High & medium risk: surgical instruments: Single-use or Destroy or Quarantine for re-use exclusively on the same patient