Prion diseases

Question 1

What causes a prion disease?

Answer 1

The change of normal cellular protein from Prp(C) to PrP(BSE/SC)

Question 2

Describe the mechanism of prion disease development

Answer 2

Question 3

List some prion diseases of animals

Answer 3

1. Bovine spongiform encephalopathy (mad cow disease)
2. Scrapie

Question 4

What is the incubation period of BSE?

Answer 4

2-8 years

Question 5

How is BSE transmitted?

Answer 5

1. Ingestion of bone-meal contaminated with mutated prion
2. Spontaneous mutation (less common in BSE)

Question 6

Which animals are more prone to infection with BSE?

Answer 6

Young animals (<6 months), but clinical signs do not appear until 3-8 years old

Question 7

Where do prions from BSE replicate once in the body?

Answer 7

In the Peyer’s patches of the ileum

Question 8

How does BSE develop (pathogenesis)?

Answer 8

1. Ingestion
2. Replicates in Peyer’s patches of ileum
3. Transported via PNS to CNS
4. Accumulates in brain

Question 9

Can sheep and goats get BSE?

Answer 9

Yes, but much less likely! More likely to suffer from scrapie

Question 10

What are the different forms of clinical disease of BSE in cattle?

Answer 10

1. Neurological disease
2. Atypical BSE

Question 11

Describe the typical clinical signs of neurological BSE

Answer 11

• Gait abnormalities
  
  • Hind limb ataxia and hypermetria
• Hyperresponsive to stimuli
• Tremors
• Behavioural changes - AGGRESSION
• Non-specific signs

Question 12

Describe the typical clinical signs of atypical BSE

Answer 12

• Inactivity
• Mental dullness
• Low carriage of head
• Kyphosis
• Sudden falling
• Hyper-responsivity to tactile stimuli (but not light or sound)

Question 13

What are the histopathological changes seen in BSE?

Answer 13

Neuronal vacuolation and non-inflammatory spongiform changes in the grey matter

Question 14

How do we diagnose BSE?

Answer 14

1. Necropsy and histopathology
2. Immunoblotting
3. Immuno-histochemistry
4. ELISA, western blot

Question 15

Why can we not use serology to diagnose BSE?

Answer 15

As the body recognises the BSE as “self-protein” and so no Ab are made

Question 16

How do we treat BSE?

Answer 16

We don’t - cull!

Question 17

List some preventative measures related to BSE control

Answer 17

• OIE reportable
• Cull cohort - any who received same feed
• Specific risk material
  
  • Taken from ALL animals >3 years old
    
    • Entire head with skin and ear tag
    • Medulla obongata
  • Slaughterhouse
    
    • All animals >72 months
    • All emergency slaughters >48 months
    • All animals >48 months showing ANY suspected clinical signs
• Cannot feed bone meal or blood meal

Question 18

Which sheep are most commonly affected by scrapie?

Answer 18

Cheviots

Suffolk

Question 19

What is the incubation period of scrapie?

Answer 19

2-5 years

Question 20

How is scrapie transmitted?

Answer 20

• Neonates - licking and ingesting foetal membranes and fluid
• Direct contact
• Contaminated fomites
• Mutation

Question 21

What are the typical clinical signs of scrapie in sheep?

Answer 21

• Separation from flock
• Hyper-excitability and hyper-metria
• Ataxia, incoordination, blindndess, convulsions
• Intense pruritus - anorexia
• Death in 2-6 weeks after clinical signs appear

Question 22

How is scrapie diagnosed?

Answer 22

1. Clinical signs
2. Immuno-histochemistry
3. Histopathology
   
   1. Brain and spinal cord
4. Western blot
5. Immunohistochemistry

Question 23

Describe the slaughterhouse monitoring of scrapie?

Answer 23

• 10 samples from each farm
• Entire head of animal or brainstem
• Taken from animals >18 months old OR
• From animals with >2 erupted permanent incisors