93. Infectious encephalopathies, scrapie, encephalopathy of minks. Flashcards
Tse affects CNS?
TSE affects CNS
- Slowly progressing
- Degenerative
- No inflammation
- Always fatal
Infectious Encephalopathies characteristics?
Infectious Encephalopathies
Characteristics
- Central nervous system
- Slow, no inflammation, degenerative processes
- Worldwide occurrence
Infectious encephalopathies etiology?
Etiology
- Virus, virino, autoimmune disease
- Prion: proteinaceous infectious particles
- 27-30 kDa protein
- Physiological prions
‣ Role is not completely known, maybe forming and maintaining long-term memory
‣ Numerous copies in neurons
‣ Continuous format and breakdown
- Pathogenic prions
‣ Structural differences
‣ Extremely good resistance against proteases, heat and disinfectants
‣ The pathogenic prions trigger the misfiling of the physiological prion proteins in a chain reaction-like process
• Origin
- Mutation is sporadic
- Infection
- Atypical prion strains
Pathogenesis of infectious encephalopathies?
Pathogenesis
- Infection: per os, im, sc, ic
- Intestine, intestinal lymph nodes
- Nerve endings in intestinal wall
- Passes along neurons (1 mm/day), n. splanchnicus, n. Vagus
- Brain and spinal marrow
- React with normal prior on cell surface
- Neurons, myocytes, B-lymphocytes
- Structural changes to normal prions
- Aggregation ➝ internal proteases unable to decompose ➝ accumulation and formation of amyloid plaques ➝
degeneration/death of cells
- Pass through peripheral nerves, eyes, tongue and nasal mucosa
- Mutation: pathogenic when it enter another species
- Infection
- Inherited: human familial accumulation
- Genetic predisposition
Pathology and diagnosis of infectious encephalopathies?
Pathology
- No pathological lesions
- Vacuolisation of nerve cells, amyloid plaques
Diagnosis
- Epidemiology, clinical signs: suspicion only
- Histopathology, EM, IHC
- Amyloid plaques
- Vacuolisation in neutron and grey matter
- Electron microscopy: detection of PrP threads ➝ BSE fibrils of different structure, SAF (scrapie-associated fibrils)
- Immuno-methods to detect prions ➝ IF, ELISA, Western blot, IHC
- Prions are not immunogenic in host but with hyperimmunisation, monoclonal antibodies can be prepared against them
Scrapie Occurrence?
Scrapie
Occurrence
- Worldwide, except Australia and New Zealand
- Less frequent, genetic resistance
- Atypical scrapie in Norway
- Sporadic everywhere including Australia and New Zealand ➝ found in epidemiological surveys
- Distinct anatomical localisation: cerebellum
- Distinct prion protein pattern
Epidemiology of scrapie?
Epidemiology
• Natural hosts: sheep, goat, mouflon
- Animals 1.5-5 years
- Long-lasting presence in flocks
- Disease carriage: tonsils, lymph nodes, intestine, nasal discharge shedding with excreta
- Frequency of occurrence increases with mixing of animals of different age groups
- Genotype
- Can be sporadic
Pathogenesis of scrapie?
Pathogenesis
- Infection: per os, close contact
- Excretes ➝ intestine ➝ spleen, lymphoreticular tissues, lymph nodes, tonsils
- Shedding with excreta, discharge, amniotic fluid and foetal membranes
- Atypical scrapie, not present in lymphoreticular tissues ➝ no shedding
Clinical signs of Scrapie?
Clinical signs
- 1.5-5 year old animals
- Changes in general behaviour
- Nervous symptoms: head tremors, nervousness
- Itching (not present in atypical form)
- Frequent bicycling with tongue movements, water consumption
- Motor disorders
- Ataxia, hypermetria, weakness, weight loss
- Death
Pathology and diagnosis of Scrapie?
Pathology
• Like other TSEs, atypical: different localisation
Diagnosis
- Like other TSEs
- Atypical: different prion structure and immunodiagnostic pattern
Prevention of Scrapie?
Prevention
- Notifiable disease
- Breeding of genetically resistant lineages
- Resistant rams: PrP gene dominant
- Culling, individual genotyping possible
- Slaughtered sheep older than 18 months ➝ obligatory test
Distribution and epidmiology, pathogenesis of Mink encephalopathy?
Distribution
- Rarely seen
- In mink herds only
Epidemiology, Pathogenesis
- Feeding with prion-contaminated meat (cattle, sheep)
- Per os infection
- Neither vertical, nor horizontal spread
- No shedding
- Animals older than 1 year
Clinical signs and prevention, Control of encephalopathy of minks?
Clinical signs
- Incubation: 6-9 months
- Changes in general behaviour
- Scattering of faeces
- Hypersensitivity
- Nervousness, somnolence
- Tail arching like squirrels
- Ataxia, convulsion, tremor, weight loss
- Death
Prevention, Control
- Culling
- Feeding of meat with no prion risk
