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Transmissible spongiform encephalopathies (TSEs) & neurological…
Transmissible spongiform encephalopathies (TSEs) & neurological disease in ruminants
TSEs
Aetiology
Prion diseases causing progressive CNS neurodegeneration.
Not highly contagious, but are transmitted through ingested of contaminated feed (swill feeding).
Main TSEs of concern are BSE and 'Scrapie' in sheep and goats.
Clinical signs
BSE
Apprehension, ataxia, hyper-/hypoesthesia, altered behaviour.
Scrapie
Pruritis, ataxia, hyper-/hypoesthesia, altered behaviour.
Diagnosis
Brain tissue samples using longitudinal/transverse craniotomy, cranial capping or spooning.
Obex (+/- eye & lumbar spinal cord) fixed in 10% formalin
As part of full PM, also sample: liver, kidney, heart, lung, spleen, LNs, serum (can be used to Dx IBR, SBE, botulism), whole blood (EDTA + smear), brain/kidney smears, GIT contents.
Prevention/surveillance (TSEFAP)
Program that functions: surveillance, quarantine/control of imported animals/products, Ruminant Feed Ban and legislation.
Annual collection of sheep/cattle brains for testing, banned importation of cattle from BSE-affected countries, banning swill feeding and ensuring all imported cattle are examined by Food Standards Australia and New Zealand.
Restricted animal material (RAM) is defined as any material taken from a vertebrate animal other than tallow, gelatin, milk products or oils. It includes rendered products, such as blood meal, meat meal, meat and bone meal, fish meal, poultry meal and feather meal, and compounded feeds made from these products.
Nutritional causes of neurological disease
Hypovitaminosis A
Sulfur toxicity
Urea toxicity
Salt poisoning
Corynetoxicoses
Staggers (phalaris, paspalum and ryegrass)
Nitrate-nitrite toxicity
Pb toxicity
Cyanotoxicoses (BG algae)
Bacterial causes of neurological disease
Listeriosis
L. monocytogenes enters wounds (usually buccal) and ascends via the trigeminal nerve to produce acute meningoencephalitis.
Typically unilateral lesions (circling etc)
Botulism
C. botulinum produced neurotoxin that causes ascending paralysis of striated/smooth muscle
Tetanus
Refer to clostridial disease chart
Metabolic causes of neurological disease
Pregnancy toxaemia
Hypocalcaemia/hypomagnesaemia
Acidosis (potantially)
Important exotic diseases
TSEs
Rabies
Visna virus
Coernurosis (GID)
Ovine encephalomyelitis
Aujesky's disease (herpesvirus)