Ovine neurology Flashcards
List development neurological diseases of sheep
- Swayback
- Dandy Walker malformation (hydrocephalus)
- Daft lamb cerebellar hypoplasia
Give examples of infectious neurological diseases of sheep
- Bacterial: meningitis, abscesses
- Viral: border disease
- Parasitic: gid
Give an example of a metabolic/nutritional cause of neurological disease in sheep
Cerebrocortical necrosis
Give an example of traumatic cause of neurological disease in sheep
Cervical subluxation due to fighting
Give examples (name, diagnosis) of neurological diseases that have an onset that is:
a: immediate
b: in minutes
c: minutes to hours
d: hours
e: hours to days
f: days
g: weeks to months
a: cervical injury, group fighting
b: hypomagnaesaemia, response to treatment
c: hypocalcaemia, response to treatment
d: cerebrocortical nercosis/polioencephalomalacia, opisthonus and response to treatment
e: pregnancy toxaemia (urine ketones and blood BHB), louping ill (tick area and time of activity), listeriosis (silage fed, possibly scour)
f: spinal abscess, progressive, increased WBC, crossover from polymorphic to lymphocytes
g: scrapies (>2yo and excessive pruritus), gid (<2yo gradual onset and progressive)
What are your differentials for a young lamb with a neurological condition from birth, that is mentally normal?
Swayback, Border disease
What are your differentials for a young lamb that is affected from birth and is mentally abnormal?
- Dystocia injury
- Border disease
- Cerebellar hypoplasia
- Severe swayback
What are your differentials for a young lamb, affected within a few weeks of birth with a neurological conditions, that is mentally normal?
- If ataxic: delayed swayback, spinal abscess
- If stiff: tetanus
What are your differentials for a young lamb, affected within a few weeks of birth with a neurological conditions, that is mentally abnormal?
- Meningitis
- Encephalitis
What are your differentials for a young lamb, affected within a few days of birth with a neurological conditions?
- If pyrexic: meningitis, encephalitis
- If treated for above and fails to feed: hypothermia, hypoglycaemia
- If subnormal temp on presentation: hypothermia, hypoglycaemia
What is your most likely differential for a growing lamb, with sudden onset paresis, mentally normal?
Cervical injury, especially in rams
What is your most likely differential for a growing lamb with sudden onset coma, opsithotonous, or strabismus?
Cerebrocortical necrosis
What is your most likely differential for sudden onset ataxia, coma, paralysis, in a growing lamb in a tick area?
Louping ill
What is your most likely differential for sudden onset cerebellar signs in a growing lamb?
Space occupying lesioin e.g. gid cyst, abscess
What are your most likely differentials for a growing lamb with gradual onset neurological signs, that is mentally normal?
- Delayed swayback
- Spinal abscess
What are your most likely differentials for a growing lamb with gradual onset cerebral or cerebellar signs?
Space occupying lesion e.g. gid cyst, abscess
What is you most likely differential for an adult/number of adults with sudden onset coma, blindness, episthotonus and strabismus?
Cerebrocortical necrosis
What are your most likely differentials for a group of ewes late in pregnancy with neurological signs?
- Hypocalcaemia
- Pregnancy toxaemia
What is your most likely differential for a group of lactating ewes showing sudden onset neurological signs?
Hypomagnasaemia
What is your most likely differential for a group of sheep with sudden onset neurological signs that are silage fed?
Listeriosis
What is your most likely differential for a group of sheep with sudden onset neurological signs that are in a tick area?
Louping ill
What is your most likely neurological differential for an adult sheep displaying gradual onset abnormal behaviour, ataxia and pruritus?
Scrapie (usually >2yrs)
What are your most likely differentials for a sheep showing gradual onset cerebral or cerebellar signs?
- Gid
- Abscess
- Maedi visna
What is the main source of infection with scrapie?
Placenta in lambing environment
Compare typical and atypical scrapie
Classical dramatically reduced due to breeding programs, but atypical probably not genetic and may not be infectious
Describe the clinical signs of scrapie in sheep
- Paresis and ataxia, esp. hindlimbs
- Quadriplegia, recumbency
- Separation from flock
- Depression, anxiey or hyperexcitability
- Head tremor, low head carriage
- Pruritus
- WEight loss, bruxism, cud dropping
- No menace response
- Usually >2yo
Outline the diagnosis of scrapie in sheep
- Detection of PrPsc in brain on post mortem
- Isolation of PrPsc in biopsy of lymphoid tissue (tonsillar tissue or rectal mucosa)
What is Maedi Visna?
2 forms of disease, visna is neurological disease, maedi is respiratory. Visna less common than Maedi in the UK
Compare maedi and visna
- Visna commonly accompanied by cachexia and chronic wasting
- Visna commonly younger than maedi (<2yo)
Describe the neurological signs of maedi visna
- Ataxia, paresis, drag a leg
- Hind legs often affected more than front but all 4 can be involved
- Depression, head tilt, fine tremor of lips
- Occasionally may appear blind
List the differential diagnoses for maedi visna and how is it diagnosed?
- Listeriosis
- Aberrant larval migration
- Spinal abscess/mass
- Scrapie
- Diagnosis by PM
What are the 2 forms of swayback?
Congenital and delayed
Compare the susceptibility of sheep breeds to swayback
- Only common in hill/upland flock
- UK breeds more susceptible e.g. Scottish Blackface vs continental breeds e.g. Texels
Describe congenital swayback (cause, signs, diagnosis)
- Copper deficiency due to little extra feed in mid-late pregnant hill ewes
- Signs: stillbirth, small weak lambs with fine head tremors, may be bright but weak on HLs, stumbling/swaying gait, fine bones and dull coats
- Histopath on brain and spinal cord showing cavitation of cerebral white matter and internal hydrocephalus, <6mg copper/kg DM brain or <10mg copper/kg liver
Describe delayed swayback (cause and signs)
- Normal at birth but progressive weakness of pelvic limbs at 2-4mo
- Demyelination and reduced myelin synthesis in spinal cord
How can delayed swayback be prevented?
- Injection of chelated copper
- Glass bolus in mid pregnancy (not for Texel or other continental breeds and primitive breeds, copper toxicity sensitive)
What is gid?
Infestation with Coenuris cerebralis, the larval stage of taenia multiceps
When does acute coenurosis occur in sheep?
10 days after turning onto land heavily contaminated with dog faeces
Describe the clinical signs of acute coenurosis in sheep
- Pyrexia, listlessness and head aversion
- death 4-5 days after neurological signs
Describe the clinical signs of chronic coenurosis in sheep, affecting the cerebral cortex
- Head pressing and depression
- Loss of menace response
- Blindness in contralateral eye
- Contralateral proprioceptive deficits
- If superficial: wide compulsive circling towards side of cyst
- If deep: narrow circling away from cyst
Describe the clinical signs of chronic coenurosis in sheep, affecting the vestibular system
Head tilt towards affected side
Describe the clinical signs of chronic coenurosis in sheep, affecting the cerebellum
- Dysmetria, ataxia, wide-based stance
- Bilateral postural deficits
- Rapid deterioration
Describe the prevalence of coenurosis in different brain regions
- 80% cerebral cortex
- 10% cerebellar
- 2% vestibular
- 8% mutliple locations
Describe the development of chronic coenurosis
- More common in growing sheep (6-18mo), very rare >3yo
- Insidious onset with slowly progressive focal lesion
- 2-6mo from larval hatching to migration and onset of neurological dysfunction
What is the signficance of coenurosis in sheep?
Zoonotic, and dog is intermediate host
What is Louping ill?
Tick transmitted Arbovirus belonging to tick-borne encephalitis complex
Describe the clinical signs of Louping ill
- Affects brain
- Causes varying degrees of incoordination, paralysis, convulsions, death
- Mortality as high as 100% in naive animals
What species can be affected by Louping ill?
- Primarily sheep
- Humans, cattle, goats, pigs, horses, farmed red deer, llamas, dogs and wild red grouse can be affected
Describe the diagnosis of Louping ill
- Serology for antibody to virus
- Most commonly diagnosed in lambs and yearlings in areas where Louping ill is endemic
- Most common when susceptible sheep first moved to Louping ill area
Describe the treatment and prevention of Louping ill in sheep
- No treatment
- Prevent by vaccination
- Dipping in OPs reduces risk but does not induce immunity
What are the most common poisonings leading to neurological in sheep?
- Lead
- Plant e.g. Bracken
- Oxalate
What is Bracken poisoning in sheep?
Ptaquiloside toxicity, causes “Bright Blindess”
Describe the clinical signs of Bracken poisoning in sheep
- Tapetal hyperreflectivity
- Permanent blindness and characteristic alert attitude
- Poor response of pupils to light
- Ophthalmic exam in advanced cases shows narrowing of arteries and veins, pale taeptum nigrum with fine cracks and spots of grey
- Bone marrow suppression
- Haemorrhage
- Immunosuppression
- Urinary tract neoplasia
Describe the histological apperance of the retina in sheep affected by Bracken poisoning
Severe atrophy of retinal rods, cones and outer nuclear layer that is most pronounced at the tapetal portion of the retina
How does oxalate poisoning occur in sheep?
- Contained in feed crop
- All beet crops concentrate oxalate in the leaves so feeding of tops as well as bulb can be dangerous
Describe the clinical signs of oxalate poisoning and the treatment and prevention
- Symptoms and treatment same as for hypocalcaemia
- Prevention by limiting % of diet that is the leaf of beet plants by strip grazing or lifting crop to just feed the bulb
Describe the clinical signs of cerebellar syndromes in sheep and give generalised and localised diseases that may cause this
- Ataxia, hypermetria, head tremor, high head carriage, jerky movement, intention tremors, usually bilateral proprioceptive defects or ipsilateral and circle towards
- Generalised: cerebellar hypoplasia, border disease, scrapie
- Localised: gid, abscess
Describe the clinical signs of cerebral syndromes in sheep and give generalised and localised diseases that may cause this
- Mental state/behaviour change, stupor, depression, hyperaesthesia, opisthotonus, head pressing, head deviation, contralateral proprioceptive defects, contralateral blindness (but normal PLR), circling towards superficial and away from deep lesions
- Generalised: CCN/PEM, bacterial meningitis, pregnancy toxaemia, scrapie
- Localised: gid, abscess
Describe the clinical signs of vestibular syndromes in sheep and give diseases that may cause this
- Head tilt with falling, rolling or circling, nystagmus
- Middle or inner ear infection (often also facial nerve paralysis and Horners syndrome)
Describe the clinical signs of pontomedullary syndromes in sheep and give diseases that may cause this
- Depression, cranial nerve deficits, ipsilateral hemiparesis, circling (VIII), facial paralysis, cheek muscle paralysis and decreased sensation, abnormal resp patterns (resp centre in medulla)
- Listeriosis
Describe the clinical signs of midbrain syndromes in sheep and give diseases that may cause this
- Depression, coma, limb rigidity, opisthotonus, normal vision with strabismus and mydriatic pupil
- Disease: hepatic encephalopathy, cranial trauma (uncommon in sheep)
Describe the clinical signs of hypothalamic syndromes in sheep and give diseases that may cause this
- Altered behaviour/mental state, hyperaesthesia, aggression, disorientation, impaired vision, dilated, poorly responsive pupils, appetite and thermoregulation affected
- Diseases: pituitary gland tumours and abscesses (not common in sheep)
What would facial nerve damage look like in a sheep?
- Drooped ear, eyelid and lips
- Food packing in cheek
Compare the strabismus that occurs with oculomotor, trochlear and abducens nerve damage
- III: lateral strabismus
- IV: dorso-medial strabismus
- VI: medial strabisumus
What would damage to the trigeminal nerve look like in a sheep?
- Decreased facial sensation
- Dropped jaw
- Saliva pooling
- Food packing in cheek
What is a common outcome of damage to the glossopharyngeal, vagus and accessory nerve in sheep?
Dysphagia
What nerve, when damaged, would lead to tongue paralysis?
Hypoglossal
Outline a prevention and treatment plan for gid in sheep
- Worm dogs every 6 weeks and remove carcasses from yard
- Surgery possible
- In 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
- Incise the dura mater and tissue filled hole, drain and remove cyst wall and protoscolices with forceps
- Provide post-op analgesia and antibiotics
- Corticosteroids to reduce post surgical brain oedema
- Euthanasia is the most rational option in 99% cases
