prions - Emily Flashcards
What is the protein-only hypothesis?
Prions self-replicate without nucleic acid by converting a normal protein into a misfolded, infectious form
What is a prion?
A proteinaceous infectious particle
______ and ______ _______ protein encoded by the same chromosomal gene
Scrapie; cellular prion
What happened to mice that had the PrP gene knocked out?
They were resistant to prion infection
What are the hypothesized functions of the PrP(c) membrane glycoprotein?
-Synaptic transmission
-Circadian rhythm
-Copper transport/release
-Signalling
-Neuroprotective
What are the biochemical characteristics of PrP(c)?
-Alpha-helical
-Soluble
-Proteinase K sensitive*
-Not infectious*
What are the biochemical characteristics of PrP(Sc)?
-B-sheet that can aggregate and form fibrils
-Insoluble
-Partially proteinase K resistant*
-Infectious*
Once PrP(c) has been converted to PrP(Sc) in the infected host, is it different in its primary structure/amino acid sequence?
NO!!!
What is the normal cellular prion protein called?
PrP(c)
Can the host make antibodies against prions?
No it cant
What are the two most important differences between viruses and prions?
-Viruses contain genetic info; prions DON’T
-Viruses illicit an immunological response (inflammatory, antibodies). Prions do not cause an adaptive immune response (no antibodies, no T-cell activation)
What do viruses contain that is different than prions?
Viruses contain DNA/RNA, protein, and sometimes a lipid coat. Prions are ONLY protein
What can viruses be deactivated by and what can prions be deactivated by?
Viruses: UV light, formaldehyde, alcohols, autoclaving at 121C
Prions: Bases that denature proteins (urea, guanidinium, salts, NaOH)
What are some important implications for diagnosis of prion disease?
Can’t use PCR or antibody detection!
What do diseases caused by prions have in common?
-Fatal
-Transmissible/infectious
-Spongiform neurodegeneration
-Long incubation time
-Short clinical phase (6 months to a year then will die)
-No treatment or prophylaxis :(
What are 3 common findings on histopathology of brain tissue infected with a prion disease?
-Spongiosis
-Gliosis
-PrP(Sc) deposition
What are 3 common methods of diagnosing prion diseases?
-Immunoblot
-ELISA
-Immunohistochemistry/histopathology
What materials can be used for diagnosing prion diseases?
-Mainly brain homogenates (obex of brain stem after dying)
-Biopsies of rectoanal mucosa-associated lymphoid tissue or retropharyngeal lymph node (before dying)
What is another potential diagnostic test that can be used for detecting prion diseases that hasn’t been approved yet?
RT-QuIC (real-time quaking induced conversion)
What is the benefit of using RT-QuIC if it was approved?
It can detect PrP(Sc) in smaller amounts than ELISA can detect
How does RT-QuIC work?
Purified recombinant PrP produced in bacteria are mixed with the sample of infectious PrP(Sc) and Thioflavin T (fluorescent) and shaken up. The fluorescent stuff binds to amyloid fibrils and emits fluorescence
What are the 3 etiologies of prion diseases?**
- Sporadic (most common)
- Inherited
- Acquired
What gene contain SNP mutations that can cause inherited prion diseases?
PRNP gene
What are the 3 most common prion diseases in animals?
- Scrapie
- BSE (bovine spongiform encephalopathy)
- CWD (chronic wasting disease)
What are the clinical signs of classical scrapie in sheep and goats?
-Behavioural changes
-Incoordination
-Tremor
-Ataxia*
-Pruritus* (most common sign)
What is the incubation period of classical scrapie?
2-5 years
How long is the clinical phase of classical scrapie?
weeks to 6 months
Where can prion proteins be shed with classical scrapie?
-Urine
-Saliva
-Feces
-Milk
How can classical scrapie be spread?
Through horizontal and vertical transmission
What is atypical scrapie/Nor98?
A sporadic form of scrapie that happens in older sheep
What are the main differences between classical scrapie and atypical scrapie?
Classical:
-Pruritus common
-Infectious
-Distributed in brainstem
Atypical:
-Pruritus uncommon
-Not contagious
-Distributed in cerebrum/cerebellum
What are the main clinical signs of atypical scrapie?
Ataxia
Incoordination
What have some sheep farmers been trying to select for in their breeding?
Sheep that have a SNP in the PrP gene that have resistance to scrapie
Are genotypes that are resistant to classical scrapie still susceptible to atypical scrapie?
Yes!
How is BSE transmitted?
Through ruminant-derived meat and bone meal
Is BSE infectious?
NO! There is no prion shedding in BSE
What material is used for testing for BSE?
Obex of brainstem
What is the incubation period for BSE?
2-8 years
Is BSE transmissible to humans and other species?
Sure is
What are behavioural changes seen in cows infected with BSE?
-Nervousness
-Anxiety
-Teeth grinding
-Frequent nose licking
-Tremors
What are sensory symptoms seen in cows infected with BSE?
Hypersensitivity to:
-Light
-Noise
-Touch
What changes in locomotion are seen in cows with BSE?
-Ataxia in hind limbs
-Pacing
-Hypermetria
-Cannot get up after laying down
What structures are included in specified risk material for BSE?
-Spinal cord
-Dorsal root ganglia
-Trigeminal ganglia
-Brain
-Retina
-Tonsil
-Distal ileum (peyers patches)
What is the strongest evidence for the origin of BSE?
That it emerged from atypical scrapie
How can BSE be acquired?
-Experimentally (injected into brain)
-Naturally (consuming BSE contaminated foods)
What species is resistant to BSE?
Dogs
What is it called when a human gets infected with BSE?
Variant Creutzfeldt-Jakob disease (vCJD)
What are the major differences between sporadic CJD and vCJD?
sCJD:
-Dementia
-Median death at 68 years
-No florid plaques in histo
-PrP(Sc) only in CNS
vCJD:
-Ataxia, psychiatric symptoms
-median age at death 28 years
-Florid plaques present
-Involvement of LRS (lymphoreticular system) (appendix) and can spread through blood transmission
Which cows get sent for testing for BSE?
-Animals >30 months that are dead, down, dying or diseased
-Any cattle exhibiting clinical signs of BSE
What is the testing procedure in Canada for BSE?
- Initial test (immunoblot, ELISA)
- Non-negative tests go to CFIA Lethbridge for same test
- Positive again -> CFIA confirmatory testing (IHC, OIE western blot)
If BSE has been confirmed on a farm, what happens?
The farm and any farms in between have to be examined for identification of equivalent risk animals
-Born 1 year before/after BSE animal = culled + tested
-Exposed to same feed as BSE animal during first year of life = culled + tested
What is atypical BSE?
-Sporadic form of BSE
-Affects older cows (>8 years)
-Low frequency
-Found in countries at very low risk for food borne classical BSE
What is the most problematic/contagious prion disease in animals?
Chronic wasting disease (CWD)
What species are affected by CWD?
-Elk
-Mule deer
-White-tailed deer
-Moose
-Reindeer/caribou
-Also farmed animals!
How is CWD transmitted?
Horizontally and vertically; typically through oral infection from contaminated soil
What is the incubation period for CWD?
23 months - 4 years
How long does the clinical phase of CWD last?
4 months to a year
What are some signs of CWD? (they are all unspecific)
-Weight loss
-Behavioural changes (deer lose fear of humans)
-Depression/isolation
-Hypersalivation
-Teeth grinding
-Incoordination
-Difficulty swallowing
-Extreme thirst and urination
-Pneumonia
What contributes to the efficient horizontal transmission of CWD?
Extra-CNS distribution and excretion of CWD prions
Is CWD increasing in Alberta wildlife?
Ya and it’s increasing a lot (~17% prevalence rn)
Explain the protein-only hypothesis again pls
Prions are self-replicating infectious proteins, consisting of misfolded isoform PrP(Sc) of cellular prion protein PrP(c)
What are the 3 main things that distinguish prions from viruses?
- No genetic info
- No immunological response (no antibodies)
- Inactivation by bases
What are the 3 etiologies of prion disease again?
- Sporadic
- Inherited (genetic)
- Acquired
What are the currently used diagnostic assays for prion diseases?
-ELISA
-Western blot/immunoblot
-Detection of PrP(Sc) with proteinase K digestion
-Brain homogenates (obex)
-Rectoanal mucosa associated lymphoid tissue and retropharyngeal lymph node biopsies (scrapie and CWD only)
