-Individual weaned lambs are usually affected approximately two weeks after movement to another pasture or other dietary change

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either event may be associated with prior anthelmintic treatment. - During the early stages affected sheep are blind and become isolated from the group and may wander aimlessly.

- dorsiflexion of the neck (‘star-gazing’).

- Affected sheep are hyperaesthetic to auditory and tactile stimuli which may precipitate seizure activity.

- Dorsomedial strabismus and spontaneous horizontal nystagmus are frequently present in both eyes.

- Trauma to the superficial branch of the facial nerve on the dependent side when recumbent may result in ptosis and drooped ear.

- The condition deteriorates within 24 - 48 hours to lateral recumbency with opisthotonus. Death follows within 3 to 5 days in untreated sheep. 

- Affected areas of the cortex may exhibit a bright white autofluoresence when cut sections of the cerebrum are viewed under ultraviolet light (Wood’s lamp; 365 nm).

This property has been attributed to he accumulation of lipofuchsin in macrophages but not all PEM cases fluoresce.

Definitive diagnosis relies upon the histological findings in the cortical lesions of vacuolation and cavitation of the ground substance with astrocytic swelling, neuronal shrinkage and necrosis. 

- Clinical signs are slowly progressive and arise from involvement of one cerebral hemisphere with contralateral blindness and proprioceptive deficits but normal pupillary light reflexes. 

- Depression common

The vestibular system helps the animal maintain orientation in its environment, and the position of the eyes, trunk and limbs with respect to movements and positioning of the head. Clinical signs depend upon whether there is unilateral or bilateral involvement, and if the disease process involves the peripheral or central components of the vestibular system. Unilateral peripheral vestibular lesions are commonly associated with otitis media and ascending infection of the eustachian tube is not uncommon in growing lambs.

Sheep with unilateral vestibular disease present with a head tilt towards the affected side and horizontal nystagmus with the fast phase directed away from the side of the lesion although the nystagmus may regress with time. Circling behaviour towards the affected side may be present. Eye droop on the affected side is usually present. Ipsilateral facial nerve paralysis frequently results from otitis media causing ptosis and drooping of the ear. 

Confirmation of the diagnosis of cerebellar abiotrophy requires histological demonstration of widespread Purkinje cell degeneration in the cerebellum.

 - Cutaneous stimulation of the skin over the dorsal sacral area (provocative scrapie test) elicits a nibble response in the majority of sheep including manic lip-smacking and swaying of the hindquarters.

Cerebral dysfunction is indicated by an altered mental state with depression and a vacant, detached appearance but hyperaesthesia to visual, auditory and tactile stimuli. Vision and pupillary light reflexes are normal. A common behavioural abnormality observed in the early stage of scrapie is that affected ewes, when stressed such as gathering with a sheepdog, appear to "collapse" and assume sternal recumbency with the neck extended and the head held on the ground for up to five to ten minutes’ duration. In this state the sheep cannot be prompted to regain its feet but will do so unaided soon afterwards and appear normal. 

Cerebellar dysfunction is indicated by postural and gait abnormalities, namely pelvic limb ataxia but with preservation of muscle strength, dysmetria, most commonly hypermetria of the thoracic limbs, and a wide-based stance. The gait abnormalities are most obvious when the animal is made to trot downhill or turn acute angles when hopping with both pelvic limbs is frequently observed. Signs indicative of a brainstem or vestibular lesion are not detected in scrapie. Frequent teeth grinding (bruxism) is a non-specific finding and can be attributed to ruminal impaction with dry fibrous material due to reduced rumination and buffering of rumen contents by saliva leading to acidosis. 

The neurological signs present as head tilt, approximately 5°- 10° from the vertical plane, and circling towards the affected side. These clinical signs result from lesions within the lateral ventricles. Some affected animals may display hypermetria and pelvic limb ataxia. There is a slow deterioration of neurological signs and affected sheep are usually destroyed on humane grounds within two months of initial recognition. 

The initial neurological signs are hypometria with reduced flexion of the distal limb joints, conscious proprioceptive deficits and reduced weight bearing affecting one pelvic limb. These signs can easily be dismissed by the farmer or veterinarian as an upper leg lameness involving either the hip or stifle joints. As the condition progresses, the dorsal surface of the hoof remains in contact with the ground when the leg is weight-bearing with characteristic knuckling of the fetlock joint. 

When correctly performed under local anaesthesia lumbosacral CSF collection is a safe procedure and there are no harmful sequelae. Collection is facilitated when the animal is positioned in sternal recumbency with the hips flexed and the pelvic limbs extended alongside the abdomen.

is the midpoint of the lumbosacral space which can be identified as the midline depression between the last palpable dorsal lumbar spine (L6) and the first palpable sacral dorsal spine (S2). The site must be clipped, surgically prepared and between 1-2 mls of local anaesthetic injected subcutaneously. The needle is slowly advanced at a right angle to the plane of the vertebral column or with the hub directed 5 caudally. It is essential to appreciate the changes in tissue resistance as the needle point passes sequentially through the subcutaneous tissue, interarcuate ligament then the sudden "pop" due to the loss of resistance as the needle point finally penetrates the ligamentum flavum into the extradural space. Once the needle point has penetrated the dorsal subarachnoid space CSF will well up in the needle hub within 2 to 3 seconds. 

Between 1 to 2 mls of CSF is sufficient for laboratory analysis and while the sample can be collected by free flow, it is more convenient to employ gentle syringe aspiration over 10 to 30 seconds. 

raniad CSF flow is blocked by the compressive lesion thus preventing equilibration in the lateral ventricles. Vertebral empyema typically results in CSF protein concentrations 5-10 times normal with a slight increase in white cell count.  

following pathological haemorrhage into the subarachnoid space

needle puncture of blood vessels on the dura,

and particularly the leptomeninges, during the sampling procedure.  

reduction and repair of pelvic limb fractures,

joint lavage,

tibial neurectomy,

vasectomy,

caesarean operation.