Transmissible Spongiform Diseases Flashcards
(38 cards)
What is the infectious agent that causes Transmissible Spongiform Diseases?
Prions
Name 4 things that prion can resist degredation by
- High Temperatures
- UV and ionising radiation
- Formaldehyde Treatment
- Proteases
What causes TSE
In terms of the prion
An infectious agent (protein) in a misfolded form
How do prions primarily spread?
Via horizontal transmission e.g saliva, blood, urine
What is the pathogenesis of the diseased/ beta form of the prion?
- Alters proteins
- Changes their conformation and turn sthem into diseased proteins
Name three characteristics of the beta sheet folding pattern
- resistant to proteases
- Aggregate and accumulate as an insoluble amyloid in neurons and neuropil
- Form large amyloid and fibrous plaques
- cause neuronal dysfunction
What happens when the activated prions enter the nervous system
they act as this transcription template
What is their general pathogenesis?
- Ingested by the small intestine
- Use M cells to enter peyers patches and dendritic cells
- Spreads through lymphatic nodules and the spleen
- Prions are then released from the dendritic cells and then enter the nervous endings in the lymphoid tissue
- Spread throughout the CNS
What is the pathogenesis of Scrapie prions?
specific to scrapie
- Amplify in large numbers in the lymphoreticuar system before spreading to the brain via the ANS
What is the pathogenesis of BSE prions?
specific
- Colonise MALT
- Spread via the ANS to the CNS
- Amplify in large numbers in the CNS and PNS
What do the macroscopic lesions of TSE look like?
- Intracytoplamsic vacuoles in neurons and neuropil
- Neuronal loss
- Gliosis
- Absence of leukocytic inflammation
What are the clinical signs of classical scrapie
- Pruritus, neurological signs (e.g ataxia)
- It is infectious
What are the clinical signs of atypical scrapie?
- Neurological signs but typically no pruritus and wool loss
- Sporadic/ Spontaneous (not transmissible in field situations)
Where are atypical scrapie lesions predominantly found?
In the cerebellum rather than the medulla oblongata
What agents cause atypical BSE?
Caused by H and L type agents
* naturally sporadic occuring form
What are the general clinical signs of BSE?
- Nervous/ Aggressive Behaviour
- Depression
- Hypersensitivity
- Abnormal posture
- Lack of coordination
- Weight loss
- Decreased Milk production
classical and atypical are not clinically distinguishable
What is the mode of transmission of Variant Creutzfeld-Jakob disease?
- Consumption of bovine meat products contaminated with BSE prion
- Blood transfusion from asymptomatic infected donor
- Ultimately fatal (no vaccine or treatment available)
What animals are affected by Chronic Wasting Disease?
- Cervids, Including deer, elk and moose
- also found in both wild and farmed deer
What arew the clinical signs of chronic wasting disease?
- Early- subtle changes in behaviour and weight loss
- Ataxia
- Repetitive walking
- Hyperexcitability
- Difficulty swallowing
- oesophageal dilation
- progressive weight loss
What three ways can you diagnostically test for BSE?
- Rapid Screening ELISA
- Western Blot
- Immunohistochemistry
brain or lymph nodes
What part of the brain would you sample?
Obex
Why would you test the obex for BSE?
These tracts are the ones where misfolded prion proteins accumulate
What is the over 30 months rule?
BSE does not develop fully in cattle until they are older. As a safeguard, a ban on cattle older than thirty months being sold as food in the UK was introduced from 1996 until November 2005.
Name 4 ways prions can enter the body
- Inhalatiom
- Via skin lesions
- in-utero transmission to the developing fetus
- ingestion
