Ovine Neurology Flashcards
Classification of neurological disease
- Developmental e.g. swayback
- Infectious e.g. GID, meningitis
* Scrapie (>2 years old, pruritus) and GID (<2 years old, gradual onset, progressive) - Metabolic/Nutritional e.g. CCN
- Toxic e.g. lead poisoning
- Injury e.g. cervical subluxation (rams)
- Peripheral nerve
Common neurological conditions in sheep
- Pregnancy toxaemia
- Hypocalcaemia
- Swayback
- Louping Ill
- GID (in hill flocks)
- Hypomagnesaemia
- Listeriosis
- CCN
- spinal abscesses
- Bacterial meningitis
SCRAPIE
- Notifiable!
- Transmissible encephalopathy (TSE)
- Caused by accumulation of a host protein- protease-resistant prion (PrPsc)
- 256 amino acids, codons vary at 136, 154 &171
- There are 5 alelles - ARR, ARH, ARQ, AHQ, VRQ
- Elicits no specific host antibody response
- Survives on pasture for 2 years
- Resistant to antibiotics
- Main source of infection, in the placenta in lambing
- Dramatically reduced since breeding programmes
- Atypical scrapie - not genetic and not infectious?
Clinical signs of SCRAPIE
- Paresis, ataxia (especially hindlimbs)
- Quadriplegia and recumbency
- Separation from rest of flock
- Depression, anxiety, hyperexcitability
- Head tremor, low head carriage
- Pruritus (‘nibble’ response)
- Weight loss, bruxism, cud-dropping
- No menace response
- Usually sheep >2 years old.
Diagnosis of Scrapie
- Detection of PrPsc in brain PME
- Isolation of PrPsc in biopsy of lymphoid tissue (tonsillar tissue or rectal mucosa)
Maedi Visna
The Maedi is the respiratory form and the Visna is the neurological form.
- Neurological (VISNA)
- cachexia and chronic wasting
- Visna is much less common than maedi
- Usually <2 years of age
- Ataxia, paretic and drag a leg (hind legs more often affected, can be all 4), depression, head tilt, tremors, blind
- DDX - listeriosis, GID, spinal abscess, scrapie
Important, but only common in hill or upland flocks (3-4% flocks positive and increasing).
SWAYBACK
Congenital swayback (Enzootic Ataxia)
- copper deficiency in mid-late pregnancy in hill ewes
- lots of stillbirth, small weak lambs with fine head tremors
- lambs bright, but weak on hind legs (swaying gait)
- fine boned and dull coats
- diagnosis - histo on brain and spinal cord - cavitation of cerebral white matter and internal hydrocephalus.
- <6mg copper/kg DM brain or <10mg copper/kg liver
Delayed swayback
- Normal at birth by progressive pelvic weakness 2-4 months
- demyelination in spinal cord
Prevention:
- Inject chelated copper or CuO needle or gice glass bolus in mid pregnancy
- BUT NOT to Texel or Scottish Black Face sheep or other continental breeds as highly susceptible to copper toxicity.
- much more common in highland flocks.
GID/ Coenurosis cerebralis
Larval stage of Taenia multiceps
- This is zoonotic and causes a lot of disease in Shepherds!
- Life cycle completes when the dog (definitive host) ingests sheep brain
- Acute coeneurosis - seen 10 days after turning onto land HEAVILY contaminated with dog faeces. Pyrexia, listlessness and head aversion. Death 4-5 days later with neuro signs.
- Chronic coenurosis - more common in growing sheep 6-18 months. V rare >3yrs. Slow onset. 2-6 months from larval hatching to migration and neuro signs.
GID clinical signs
Cerebral cortex (80% cases)
- Head-pressing and depression
- loss of menace response
- Blindness in contralateral eye
- Contralateral proprioceptive deficits
- Wide compulsive circling towards side of cyst - if superficial
- Narrow circling away from cyst - if deep
Vestibular
- head tilt towards affected side
Cerebellar (10% cases)
- dysmetria, ataxia, wide based stance
- bilateral postural deficits
- rapid deterioration
*8% cases there are cysts in multiple locations
GID/ Coenurosis - control
Control:
- Worm dogs every 6 weeks and remove all carcasses
Surgery is possible
- give corticosteroids to decrease post-surgical brain oedema
- cerebrum - trephine 1-2cm lateral to midline and rostral to coronal suture line
-
cerebellum - trephine midline between nuchal line and suture between occipital and parietal bones
- drain and remove cyst wall and protoscolices with forceps
- post-op analgesia and antibiotics
Euthanasia is the best option in 99% cases!
LOUPING ILL
- This is zoonotic!
- tick-transmitted Arbovirus belonging to the tick-borne encephalitis complex (TBE)
- in-coordination, paralysis, convulsions, death
- mainly seen in sheep (also humans, cattle, goats, pigs, horses etc)
-
Diagnosis:
- serology for antibody to the virus
-
Treatment:
- none
-
Prevention:
- Vaccination
- Dipping in Organophosphate
- Reduces risk but does not induce immunity
Poisoning
Oxalate Poisoning:
- All beet crops concentrate oxalate in their leaves so grazing can be dangerous
- Symptoms are the same as for hypocalcaemia, as is the treatment.
- Prevention - limit % of diet that is leaf by strip grazing of lifting crop to feed just the bulb
- Can control by giving another source of long fibre and restricting access with electric fence to fodder beet.
Diagnosing Neurological Disease (site of lesions)
Cerebellar syndrome
- Ataxia and hypermetria (high-stepping)
- Head tremor and high head carriage
- Jerky movements and intention tremors
- Usually bilateral proprioceptive defects or ipsilateral and circle towards
Generalised: daft lamb (hypoplasia), border disease, scrapie
Localised: GID, abscess
Diagnosing Neurological Disease (site of lesions)
Cerebral Syndrome:
- Mental state/behaviour change - compulsive walking, circling, jaw movements
- stupor, depression, hyperaesthesia, opisthotonus, head-pressing, head deviation
- Contralateral proprioceptive defects
- Contralateral blindness (normal PLR)
- Circling towards superficial lesions and away from deeper.
Generalised: CCN/PEM, bacterial meningitis, pregnancy toxaemia, scrapie
Localised: GID, abscess
Diagnosing Neurological Disease (site of lesions)
Vestibular Syndrome
- Head tilt with falling, rolling or cicling
- Nystagmus
E.g. middle or inner ear infection
Nb - facial nerve VII and sympathetic nerves to eye run close to middle ear so associated with facial nerve paralysis and horners syndrome (miosis, ptosis, 3rd eyelid), normal PLR and menace.
Diagnosing Neurological Disease (site of lesions)
- Depression and cranial nerve deficits
- Ipsilateral hemiparesis
- Circling (VIII) - abducens
- Facial paralysis (VII)
- cheek muscle paralysis and decreased sensation (V)
- Abnormal respiratory patterns (respiratory centre in medullar)
E.g. LISTERIOSIS
Diagnosing Neurological Disease (site of lesions)
Midbrain:
- depression, coma, limb rigidty, opistotonus, normal vision with strabismus and mydriatic pipil
e.g. hepatic envephalopathy, cranial trauma (not common)
Hypothalmic:
- altered behaviour/mental state
- hyperaesthesia, aggression, disorientation
- impaired vision, dilated, poorly responsive pupils
- appetite and thermoregulation affected
e.g. pituitary gland tumours and abscesses (not common in sheep)
