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VETM 422: Virology > prions - Emily > Flashcards

prions - Emily Flashcards

1
Q

What is the protein-only hypothesis?

A

Prions self-replicate without nucleic acid by converting a normal protein into a misfolded, infectious form

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2
Q

What is a prion?

A

A proteinaceous infectious particle

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3
Q

______ and ______ _______ protein encoded by the same chromosomal gene

A

Scrapie; cellular prion

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4
Q

What happened to mice that had the PrP gene knocked out?

A

They were resistant to prion infection

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5
Q

What are the hypothesized functions of the PrP(c) membrane glycoprotein?

A

-Synaptic transmission
-Circadian rhythm
-Copper transport/release
-Signalling
-Neuroprotective

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6
Q

What are the biochemical characteristics of PrP(c)?

A

-Alpha-helical
-Soluble
-Proteinase K sensitive*
-Not infectious*

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7
Q

What are the biochemical characteristics of PrP(Sc)?

A

-B-sheet that can aggregate and form fibrils
-Insoluble
-Partially proteinase K resistant*
-Infectious*

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8
Q

Once PrP(c) has been converted to PrP(Sc) in the infected host, is it different in its primary structure/amino acid sequence?

A

NO!!!

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9
Q

What is the normal cellular prion protein called?

A

PrP(c)

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10
Q

Can the host make antibodies against prions?

A

No it cant

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11
Q

What are the two most important differences between viruses and prions?

A

-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)

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12
Q

What do viruses contain that is different than prions?

A

Viruses contain DNA/RNA, protein, and sometimes a lipid coat. Prions are ONLY protein

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13
Q

What can viruses be deactivated by and what can prions be deactivated by?

A

Viruses: UV light, formaldehyde, alcohols, autoclaving at 121C

Prions: Bases that denature proteins (urea, guanidinium, salts, NaOH)

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14
Q

What are some important implications for diagnosis of prion disease?

A

Can’t use PCR or antibody detection!

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15
Q

What do diseases caused by prions have in common?

A

-Fatal
-Transmissible/infectious
-Spongiform neurodegeneration
-Long incubation time
-Short clinical phase (6 months to a year then will die)
-No treatment or prophylaxis :(

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16
Q

What are 3 common findings on histopathology of brain tissue infected with a prion disease?

A

-Spongiosis
-Gliosis
-PrP(Sc) deposition

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17
Q

What are 3 common methods of diagnosing prion diseases?

A

-Immunoblot
-ELISA
-Immunohistochemistry/histopathology

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18
Q

What materials can be used for diagnosing prion diseases?

A

-Mainly brain homogenates (obex of brain stem after dying)
-Biopsies of rectoanal mucosa-associated lymphoid tissue or retropharyngeal lymph node (before dying)

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19
Q

What is another potential diagnostic test that can be used for detecting prion diseases that hasn’t been approved yet?

A

RT-QuIC (real-time quaking induced conversion)

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20
Q

What is the benefit of using RT-QuIC if it was approved?

A

It can detect PrP(Sc) in smaller amounts than ELISA can detect

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21
Q

How does RT-QuIC work?

A

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

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22
Q

What are the 3 etiologies of prion diseases?**

A
  1. Sporadic (most common)
  2. Inherited
  3. Acquired
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23
Q

What gene contain SNP mutations that can cause inherited prion diseases?

A

PRNP gene

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24
Q

What are the 3 most common prion diseases in animals?

A
  1. Scrapie
  2. BSE (bovine spongiform encephalopathy)
  3. CWD (chronic wasting disease)
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25
Q

What are the clinical signs of classical scrapie in sheep and goats?

A

-Behavioural changes
-Incoordination
-Tremor
-Ataxia*
-Pruritus* (most common sign)

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26
Q

What is the incubation period of classical scrapie?

A

2-5 years

27
Q

How long is the clinical phase of classical scrapie?

A

weeks to 6 months

28
Q

Where can prion proteins be shed with classical scrapie?

A

-Urine
-Saliva
-Feces
-Milk

29
Q

How can classical scrapie be spread?

A

Through horizontal and vertical transmission

30
Q

What is atypical scrapie/Nor98?

A

A sporadic form of scrapie that happens in older sheep

31
Q

What are the main differences between classical scrapie and atypical scrapie?

A

Classical:
-Pruritus common
-Infectious
-Distributed in brainstem

Atypical:
-Pruritus uncommon
-Not contagious
-Distributed in cerebrum/cerebellum

32
Q

What are the main clinical signs of atypical scrapie?

A

Ataxia
Incoordination

33
Q

What have some sheep farmers been trying to select for in their breeding?

A

Sheep that have a SNP in the PrP gene that have resistance to scrapie

34
Q

Are genotypes that are resistant to classical scrapie still susceptible to atypical scrapie?

A

Yes!

35
Q

How is BSE transmitted?

A

Through ruminant-derived meat and bone meal

36
Q

Is BSE infectious?

A

NO! There is no prion shedding in BSE

37
Q

What material is used for testing for BSE?

A

Obex of brainstem

38
Q

What is the incubation period for BSE?

A

2-8 years

39
Q

Is BSE transmissible to humans and other species?

A

Sure is

40
Q

What are behavioural changes seen in cows infected with BSE?

A

-Nervousness
-Anxiety
-Teeth grinding
-Frequent nose licking
-Tremors

41
Q

What are sensory symptoms seen in cows infected with BSE?

A

Hypersensitivity to:
-Light
-Noise
-Touch

42
Q

What changes in locomotion are seen in cows with BSE?

A

-Ataxia in hind limbs
-Pacing
-Hypermetria
-Cannot get up after laying down

43
Q

What structures are included in specified risk material for BSE?

A

-Spinal cord
-Dorsal root ganglia
-Trigeminal ganglia
-Brain
-Retina
-Tonsil
-Distal ileum (peyers patches)

44
Q

What is the strongest evidence for the origin of BSE?

A

That it emerged from atypical scrapie

45
Q

How can BSE be acquired?

A

-Experimentally (injected into brain)
-Naturally (consuming BSE contaminated foods)

46
Q

What species is resistant to BSE?

A

Dogs

47
Q

What is it called when a human gets infected with BSE?

A

Variant Creutzfeldt-Jakob disease (vCJD)

48
Q

What are the major differences between sporadic CJD and vCJD?

A

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

49
Q

Which cows get sent for testing for BSE?

A

-Animals >30 months that are dead, down, dying or diseased
-Any cattle exhibiting clinical signs of BSE

50
Q

What is the testing procedure in Canada for BSE?

A
  1. Initial test (immunoblot, ELISA)
  2. Non-negative tests go to CFIA Lethbridge for same test
  3. Positive again -> CFIA confirmatory testing (IHC, OIE western blot)
51
Q

If BSE has been confirmed on a farm, what happens?

A

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

52
Q

What is atypical BSE?

A

-Sporadic form of BSE
-Affects older cows (>8 years)
-Low frequency
-Found in countries at very low risk for food borne classical BSE

53
Q

What is the most problematic/contagious prion disease in animals?

A

Chronic wasting disease (CWD)

54
Q

What species are affected by CWD?

A

-Elk
-Mule deer
-White-tailed deer
-Moose
-Reindeer/caribou
-Also farmed animals!

55
Q

How is CWD transmitted?

A

Horizontally and vertically; typically through oral infection from contaminated soil

56
Q

What is the incubation period for CWD?

A

23 months - 4 years

57
Q

How long does the clinical phase of CWD last?

A

4 months to a year

58
Q

What are some signs of CWD? (they are all unspecific)

A

-Weight loss
-Behavioural changes (deer lose fear of humans)
-Depression/isolation
-Hypersalivation
-Teeth grinding
-Incoordination
-Difficulty swallowing
-Extreme thirst and urination
-Pneumonia

59
Q

What contributes to the efficient horizontal transmission of CWD?

A

Extra-CNS distribution and excretion of CWD prions

60
Q

Is CWD increasing in Alberta wildlife?

A

Ya and it’s increasing a lot (~17% prevalence rn)

61
Q

Explain the protein-only hypothesis again pls

A

Prions are self-replicating infectious proteins, consisting of misfolded isoform PrP(Sc) of cellular prion protein PrP(c)

62
Q

What are the 3 main things that distinguish prions from viruses?

A
  1. No genetic info
  2. No immunological response (no antibodies)
  3. Inactivation by bases
63
Q

What are the 3 etiologies of prion disease again?

A
  1. Sporadic
  2. Inherited (genetic)
  3. Acquired
64
Q

What are the currently used diagnostic assays for prion diseases?

A

-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)

VETM 422: Virology (20 decks)

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