Transmissible Spongiform Diseases Flashcards
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
Name 5 ways prions can be shed from the body
- Nasal secretions
- Saliva
- Secretion in milk/ Colostrum
- Excretion via faeces or urine
- Contamination with the environment e.g via the placenta/ gestational tissues
What is the pathological finding of TSE?
- metabolic dysfunction of neurons and neural cells caused by the conversion of normal cellular prion protein to an abnormal form and the accumulation of this in neurons, neural cells and extracellularly within the neuropil
What are the potential differentials for scrapie?
- Paratuberculosis
- Endoparasites
- Cobalt deficiency
- External parasites, photosensitivity
- Rabies
- Toxins
What causes classical BSE?
Consumption of contaminated feed
Where is atypical BSE usually identified?
Only identified in older bovines when conducting intensive surveillance
How is chronic wasting disease usually spread
- Horizontal transmission by direct contact and the environment, including fomites
- vertical transmission has been documented in some species
What are the three areas of the brain you could sample for BSE?
- Nucleus of the solitary tract
- Nucleus of the spinal tract of the trigeminal nerve
- Dorsal motor nucleus of the vagus nerve
What is the main control/ Prevention for TSE?
- There is no known treatment
- Disease is progressive and ultimately fatal
What three TSE controls are in place?
- The feed ban
- Specified risk material control
- Bon on mechanically recovered meat
What three TSE legislations are in place?
- Legislation 999/2001- rules for prevention, control of TSE in livestock
- TSE regulations 2018
- TSE and animal by-product amendment regulations 2019
What is the passive surveillance of TSE?
- animal with clincial signs is reported to the APHA
- such cases are often slaughtered and brain is examined
What is the active surveillance for TSE?
- Testing cattle since July 2001
- Testing sheep and goats since january 2002
- Conducted a survey in 2007 and 2008
What happens if you suspect BSE?
- report to the APHA (notifiable)
- potentially movement restriction
- identification of cohort and offspring animals
- herd restrictions may be lifted
- offspring culled
What are the best ways of controlling scrapie?
- Scrapie monitoring scheme
- Genetic screening for resistance
- Buying resistant animals
- Make sure milk is from herd taht are scarpie free/ have been continually monitored
- Remove fetal membranes= source of infection
