9 - Prion Diseases Flashcards
(56 cards)
Why is BSE a one health issue? CWD?
BSE: agricultural, industry generation, distribution of infectious prions
CWD: transport of infectious animals, environmental reservoir of infectivity
How are prions unique pathogens?
They are acellular, non-living and are disease-specific protein structure (do not have their own genome)
The cellular prion protein is present in… What gene is it encoded by?
in all mammals
Encoded by prion protein gene (PRNP)
What happens when there is a prion infection? How (3)
Conversion of normal to misfolded (abnormal) prion protein
- presence of misfolded (prion mechanism)
- spontaneously
- PRNP gene alterations
How can the PRNP gene alteration affect likelihood of misfolding?
Changes in normal prion protein
Makes conversion to misfolded more or less likely depending
Healthy vs disease-causing prion protein
PRP^c (healthy): enriched in a-helices, glycoprotein cell surface, metal homeostasis, necessary for prion infection
PRP^TSE: same a.a. sequence, enriched in B-sheets, partially resistant to proteinase K digfestion
What is the difference between a prion and a prion protein?
Prion: infectious, transmissible protein agent
Prion protein: non-infectious form (PrP^C), infectious form (PrP^TSE, Sc, etc)
Slides 9-12
Look
What species can be affected by prion diseases? Which are not?
Sheep, cervids, mink, camel, cats, humans, cows, mice
Not: horses, dogs
Three categories of human prion diseases
- Acquired:
- kuru
- variant creutzfeldt jakob disease (vCJD)
- Iatrogenic CJD - Familial:
- familial CJD
- fatal familial insomnia
- gerstmann-straussler-scheinker syndrome - Idiopathic (sporadic)(85%):
- sporadic CJD
- sporadic fatal insomnia
Explain the basic of prion diseases
- spongiform degeneration
- transmissible (not all contagious)
- infection highest in brain and spinal cord. Also lymphatic
- accumulation of PrP^TSE, BSE, etc
- long incubation period
- extended preclinical stage
- fatal, no cure
- resistant to inactivation
Prion infectivity in hamsters, cattle, deer
Hamsters: 1-10 billion infectious units
Cattle: 1-10 million infectious units/gram of brain tissue
Deer: unknown
What are prions resistant to?
- chemical inactivation (acids, base, detergent)
- standard sterilization methods (autoclaving/medical sterilization: 120C 20 min)
- common UV and gamma irradiation levels
How do we inactivate prions?
Extreme conditions
- 1 N NaOH
- autoclaving at 134C for 1 hour
How do we detect prion diseases
- postmortem
- brain tissue
- distinguish abnormal protein from normal (infectious agent)
- clinical behaviour / characteristics (but occur late in disease)
Antibody response not useful
How long is the preclinical stage in deer? Cattle? Sheep? Humans
Deer (CWD) = years
Cattle (BSE) = years
Sheep (scrapie) = years
Humans (CJD) = decades
How do you distinguish normal from abnormal prions
Expose them to proteinase K, abnormal form is resistant
Slides 23-27**
Commercial detection kits for prions
Western blot or ELISA
government restrictions in place on purchase
What are PMCA and RT QuIC
PMCA: protein misfolding cyclic amplification
RT QuIC: real time quaking induced conversion
Highly sensitive technologies for detection of PrP^SC. Required expensive equipment and lab expertise.
Slide 30
Similarities and differences between PMCA and RT QuIC
Both can amplify detectable levels of abnormal prion proteins form small amounts of starting material
Both require PrP^c
PMCA uses PrP^c source from brain homogenate whereas RT-QuIC uses PrP^c from recombinant sources
Which prion diseases are transmissible? Contagious?
Transmissible: all
Contagious: scrapie & CWD
Characteristics that distinguish diff prion diseases
- contagious?
- length of incubation period
- clinical symptoms
- PK resistance
- size of PK resistant proteins
- distribution and size of spongiform lesions in brain
- interspecies transmission
Sheep scrapie vs BSE
Both transmissible from brain tissue
Sheep scrapie also contagious (sheep to sheep)
First recorded scrapie case in UK? Canada?
UK: ~1700
Canada: 1938
