7. Prionoses, BSE and Scrapie Flashcards
What are prions? Describe
Prions are a self-replicated protein structure with very special properties.
- They are NOT a virus.
- They are modified into accumulated abnormal folded host-prion protein –> “Protein folding disease” causing neuronal degeneration due to triggered cell death.
- Proteins are resistant to most treatments and disinfectants.
- Rapidly progressive and always fatal.
!!!! The protein that prions are made of “PrP”, is found throughout the body, in both healthy animals and humans
Talk about “good and the bad” prion proteins and their short pathogenesis
Prp = protein that becomes prions.
PrpC - good protein. Normal cellular protein that can replicate into copies of prions (PrpSc). The normal cellular protein is found on the surface of neurons.
PrpSc - bad protein and resistant to proteases
Cannot be degraded in the body and accumulates in the tissue
What does misfolded prions cause?
TSE (Transmissible spongiform encephalopathies
= Chronic, neurodegenerative, fatal disease.
Spongiform = brain looks like a sponge
Name diseases caused by prions
- Creutzfeldt-Jakob disease (CJD) - humans
- Bovine Spongiform encephalophathy (BSE) “Mad cow disease” - OIE. Zoonotic if infection is spread to brain and spinal cord
- Scrapie - Sheep & goats. OIE
- Feline Spongiform encephalopathy (FSE) - Cat
- Chronic wasting disease (CWD) - wild ruminats
What are two important things to mention about BSE
OIE + zoonotic
Assumed to be zoonotic due to its assumed link with the emergence of variant CJD in man
What agent are causing BSE?
Prions
What are susceptible host for BSE?
Cattle
What does BSE cause in host?
Neurological degeneration.
2 forms:
- Classical –> after ingestion of prion contaminated feed
- Atypical –> spontaneously occurence
How is BSE transmitted?
Horizontal - Ingestion of infected meat or bone (horizontal)
Cattle from beginning infected from feed.
Spontaneously or transplacental transmission but low levels.
What is the pathogenesis of BSE?
Ingestion of meat/bone –> tonsils and peyer’s patches ro replicate
Migrate to PNS –> CNS then affecting spinal cord, nerves and brain tissue.
Once infected –> infected for life!
It is a slow development and IP in cattle can last between 2 - 8 years.
Once clinical signs starts to appear it is “too late”, animal will die
Clinical signs of BSE
- Behavioral changes
- Light or external sensitivity
- Nervous or aggressive behavior
- Pruritus
- Good appetite but still wasting!
- Postpartum put them higher at risk
- High lifting limbs and muscle/ limb incoordination, loosing balance, falling etc.
How is BSE diagnosed?
Only post-mortem
Sample: Spinal cord, brain stem or whole head with skin taken at slaughter house or at farm - BY VET.
- Look at brain and sponge appearance
- Western blotting/Immuno blotting (one line is positive)
- Rapid test ELISA –> detect prions (+)
- Confirmatory test to confirm presence or if earlier shown an undoubtful result
What is treatment for BSE and Scrapie?
No treatment! Kill animal, report to OIE
BSE - When clinical signs appear the disease is too far developed. The brain tissue is too damaged and not possible for brain to regenerate.
Animal dies shortly after showing clinical signs or if detected should be killed.
How can BSE and Scrapie be prevented?
- By having closed herd systems
- Not feeding bone and meat meal.
- Kill infected animal.
- Not mix animals
- Burning of dead animals, disinfection with hypochloride
“Cohort” - Animals born in same herd and stays for 12 months together. Animals has to be separated, necropsy done within 48h
What is an important thing to mention about Scrapie?
Its OIE-listed
What are typical risk materials for BSE during sampling?
Spleen, intestine, brain, eyes, tonsils and spinal cord in animals older than 12 months.
Each organ must be removed and marked that they have not been in contact with meat sold for meat consumption.
What is the agent responsible for causing Scrapie?
Prions
What are susceptible hosts for Scrapie?
Sheep and sometimes goat
What does Scrapie cause in host?
Neurological degeneration.
2 forms:
- Classical
- Atypical scrapie –> Believed to have spontaneous occurence and without pruritus
Believed it is some genetic predisposition in some individuals.
What is transmission of Scrapie?
Horizontal - eating bone and meat from infected animal, eating/licking infected placenta or milk.
Spontaneous occurence
Vertical - Period of parturition or in transplacental
Transmission in sheep and goat is by licking of infected placenta, vertically, formites,through skin damages, vaccination, and to some degree genetic predisposition.
What is pathogenesis of Scrapie?
Ingestion of virus –> tonsils and lymphoid tissue to replicate –> entry of PNS and neural tissue of small intestine –> CNS (spinal cord and medulla oblongata)
Incubation period: Up to 5 years and once clinical signs appear they live 3 months up to 1 year. Death is always 100%
Virus can be detected in CNS (brain and spine), tonsils,
ln, saliva, spleen, muscle, and placenta.
What are clinical signs of Scrapie?
Pruritus - scratching to objects, loss of wool and coat
CNS - ataxia, behavioral change (leaving its flock) nervousness, excitement, convulsions, incoordination, tremors.
How is Scrapie diagnosed?
Only from dead animals
- Look at brain and sponge appearance
- Western blotting/Immuno blotting (one line is positive)
- Rapid test ELISA –> detect prions (+)
How can Scrapie be prevented?
- Having a closed herd
- Kill infected or suspected animals (not in US)
- Separate placenta from other animals fast
- Don’t give meat or bone meal.
What is scrapie?
A form of TSE (transmissible spongiform encephalitis) caused by prions (self-replicated proteins using host cellular proteins for conversion to prion proteins, called PrPsc).
A neurodegenerative disease found worldwide, but mainly in Europe and USA
