TSEs Flashcards
What causes TSE disease
infectious prion protein
All animals, including humans have a PRP gene that codes for protease resistant proteins aka prion proteins.
PRPc (PRP cellular) can change into different PRPs e.g. PRPSc which is scrapie
PrPc and PrPSc have an identical amino acid sequence (primary structure) but they differ in conformation (tertiary structure)
PrPSc is partially resistant to digestion. In a normal cell, PrPc is constantly made and digested; PrPSc is not digested and so accumulates – leading to cellular pathology and disease.
PRPSc, replicates causing disease and trigger PRPc around it to convert to sc too
Characteristics of TSE disease
- Long incubation
- Progressive disease, invariably fatal
- Cell death in brain gives rise to holes in the brain hence spongiform texture
- no sign of infection
Why is there no sign of infection in the brain with TSEs?
Disease is caused by your own proteins therefore there is no……
signs of fever or inflammation
No antibody response
No signs of a pathogen with a genome
These are what we look for with ID = why still not fully understood
No sign of infection!
Clinical signs of scrapie
Ataxia, tremors, rubbing, scratching, loss condition and death 1-3 months
irritation
repeated rubbing and scratching of flanks and hindquarters against objects
nibbling or grinding of teeth when rubbing themselves or when rubbed firmly on the back
continued scratching of the shoulder or ear with a hind foot
unusual or agitated nibbling of the feet, legs or other parts of the body
excessive wool loss or damage to the skin
changes in behaviour
becoming excitable
drooping ears
increased nervousness or fear response
lagging behind
aggression
depression or vacant stare
changes in posture and movement
trembling (mainly of the head)
unusual high stepping trot in early stages
severe lack of coordination
stumbling
standing awkwardly
weak hind legs unable to stand later clinical signs weight loss death
What to do if suspect scrapie?
You must immediately inform your local Divisional Veterinary Office or Scrapie Section
A DEFRA Veterinary Officer (VO) should visit within 48 hours to examine the suspected sheep.
Incubation period of scrapie
2-5 yrs
How do sheep catch scrapie?
Vertical - mother to offspring (in utero)
Pseudo-vertical - parent to offspring (lambs infected at birth from infected birth tissue
Horizontal- adult to adult/ lamb (infected sheep spread to naive adult sheep)
Contaminated land- adult to adult/lamb (land where infected sheep used to live)
Iatrogenic - adult to adult/lamb (needle contamination)
Progression to disease is under strong genetic control.
What is seen in scrapie distribution that is different in BSE in cattle
Scrapie PrPSc is widely disseminated in sheep tissues; this is not seen for BSE in cattle
Can all sheep get scrapie?
some have PrP alleles that make resistance or susceptible
15 possible combinations highest risk group is genotype VRQ/VRQ
national scrapie plan 2 main components
- Scrapie-free farms (voluntary scheme)
Lambs and sheep genotyped at no cost to see what they were, under condition that those bearing VRQ allele will be culled. – removIng susceptible from healthy flock - Scrapie-infected farms (compulsory scheme).
Slaughter of entire flock (with later restocking) OR compulsory genotyping of entire flock, followed by culling of all animals encoding VRQ (except ARR/VRQ
BSE in cattle characterised by
ataxia, nervous or aggressive behaviour, loss of condition and death 1-6 months
Incubation period BSE in cattle
5+ yrs
How is BSE transmitted?
oral route (MBM) - eating BSE material
What controls do they put in place to prevent BSE risk to consumers
Specified risk material control - remove parts of the animal most likely to contain BSE from food chain
no cattle to enter food chain over 30 months old
What is the only naturally transmitted TSE?
Chronic wasting disease = only TSE of wild populations
