Transmissible Spongiform Encephalopathies Flashcards
What is TSE in sheep?
Scrapie
What is TSE in cattle?
BSE
What is TSE in deer?
CWD
chronic wasting disease
What is TSE in humans?
variant Creutzfelt-Jakob disease
What causes TSE?
*PRP - protease resistant protein
*PRPc + PRPsc = identical amino acid sequence but different tertiary structure
*PRPsc converts PRPc into itself - PRPsc is partially resistant to digestion + accumulates = disease + death
What are the characteristics of TSE?
- Long incubation period
- Progressive and invariably fatal
- Holes in brain give spongiform texture
- No signs of fever
- No signs of inflammation
- No antibody response
- No signs of a pathogen with a genome
- No sign of infection
What are the clinical signs of scrapie?
*Ataxia
*Tremors
*Rubbing / scratching
*Loss of condition
*Death in 1-3 months
What is the incubation period of scrapie?
2-5 years
How can sheep catch scrapie?
*Vertical
*Pseudo-vertical
*Horizontal
*Contaminated land
*Iatrogenic
How does Vertical transmission of scrapie occur?
Mother to offspring
*in utero
How does Pseudo-vertical transmission of scrapie occur?
Parent to offspring
*Lambs infected at birth - from infected birth tissues
How does horizontal transmission of scrapie occur?
Adult to adult / lamb
*Infected sheep spread infection to naive adult sheep in same flock
How does contaminated land transmission of scrapie occur?
Sheep catch scrapie on land where infected sheep used to live - decades before
How does Iatrogenic transmission of scrapie occur?
Needle contamination
What are the important PrP alleles in
UK sheep?
What codons are disease linked with scrapie?
*ARR - resistance
*AHQ - resistance with VRQ
*ARQ - susceptibility
*ARH - susceptibility with VRQ
*VRQ - susceptibility
Codons = 136, 154 + 171
(ARR = Alanine coded at 136, aRginine coded at 154 + 171)
What is the highest risk genotype?
VRQ/VRQ
most cases = ARQ/VRQ - common genotype
What are the clinical signs of BSE?
*Ataxia
*Nervous / aggressive behaviour
*Loss of condition
*Death in 1-6months
What is the incubation period of BSE?
5 years or more
What is the most common transmission route of BSE?
Oral route
Why were dairy cattle more predisposed to BSE?
Ate more ‘meat + bone meal’ (MBM)
What were the BSE controls to prevent transmission?
- 1988: ban on the use of ruminant-derived protein in ruminant feedstuffs; aka “The Ban”
- 1990: ban on the use of Specified Bovine Offals in all animal feed (including pet food) in GB
*1994: ban on the use of mammalian protein in ruminant feed stuffs; - 1996: prohibited the feeding of mammalian Meat and Bone
Meal (MBM) to all farmed livestock including fish and horses; aka “The Real Ban” - 2001: Europe-wide ban on the feeding of processed animal protein to food-animals.
What were the BSE controls to prevent risk to consumers?
- Specified risk material control – remove parts of animal most likely to contain BSE from food chain
- Removed brain and spinal cord [brain was often used as thickener – cheaper than eggs!]
- Later, removed beef-on-the-bone
- Ban on ‘mechanically-recovered meat’ from rendering plants
- Used in burgers, sausages, pies and mince
- Over 30 months rule – no cattle to enter food chain if over 30 months old
What is the only naturally transmitted TSE?
Chronic wasting disease in deer
CWD
What is the incubation period of CWD?
16 months
What are the clinical signs of CWD?
*Loss of condition
*Standing apart from herd
*Listlessness
*Ataxia
*Nervousness
*Excessive drinking + urination
What is a common cause of death of CWD?
Aspiration penumonia
How is CWD transmitted?
Urine + saliva infectious
= deer shed infectious prions ono herbage which is the eaten by other deer
What are the clinical signs of vCJD?
- psychiatric: depression, anxiety, delusions, hallucinations;
- Neurological: ataxia, chorea (dance-like motion of twisting & turning), myoclonus (involuntary muscle spasm), dementia
How was human to human transmission of vCJD reduced?
- Restrictions on use of UK blood for transfusions
- Disposable surgical equipment
- Non-sharing of contact lenses
