The Clinical Neurology of Scrapie in Irish Sheep

Abstract

One hundred twenty-nine sheep with scrapie were identified from 20 flocks in which scrapie previously had been confirmed. Physical and neurologic examinations were performed on all animals. Videotape recordings were made and reviewed to assess gait. These procedures were repeated in 46 sheep at 2-to 3-week intervals until recumbency or inappetence necessitated euthanasia. Confirmation of scrapie was made by histopathologic and immunohistochemical examinations of brain tissue. The clinical signs most frequently recorded in the 129 animals on initial presentation were hindlimb ataxia (71%), head tremor (61%), altered mental status (57%), positive nibble reflex (51%), crouching posture (51%), teeth grinding (44%), low head carriage (38%), body condition score (BCS) Ͻ1.5 (38%), and conscious proprioceptive deficits of the hindlimbs (36%). Progression of the disease was characterized by an increase in the frequency and severity of ataxia, weakness and hypermetria of the hindlimbs, a decreasing sway response, a decreasing extensor response to thoracolumbar pressure, and a reduction in the BCS. No effect of farm of origin on the clinical presentation could be shown. The presence of a nibble reflex was strongly associated (P Ͻ .0005) with prion protein (PrP) genotypes AA 136 RR 154 QH 171 and AA 136 RR 154 QQ 171 . Logistic regression modeling of groups with associated clinical signs showed that animals with a crouching posture (odds ratio [OR], 20.036) and an abnormal yield to thoracolumbar pressure (OR, 7.117) were at increased risk of ataxia. Pruritus (OR, 0.168) was negatively associated with ataxia. Pruritus (OR, 4.974) and teeth grinding (OR, 4.279) were associated with a positive nibble reflex.

Clinical findings in two cases of atypical scrapie in sheep: a case report

“…Pruritus is a clinical sign usually associated with classical scrapie but its occurrence can vary significantly. In a recent study in Ireland, only 25% of 129 examined sheep displayed pruritus [2] whilst other studies in Italy and the UK reported pruritus in approximately 85% of 550 sheep [1] and 86% of 35 sheep [17] respectively. Ataxia was observed in 79.5% of 116 scrapie-affected sheep in Ireland and in 80% of sheep in the Italian study [1], whilst it was seen in all 35 sheep in the UK [17].…”

“…Ataxia was observed in 79.5% of 116 scrapie-affected sheep in Ireland and in 80% of sheep in the Italian study [1], whilst it was seen in all 35 sheep in the UK [17]. The reason for this variation is poorly understood but it may be the effect of genotype [2], breed or strain, which are thought to be the cause for the variation in the neuropathology in classical scrapie [18-20]. …”

“…Although signs of pruritus, such as rubbing, scratching or nibbling parts of the body, were neither reported by the farmer nor observed at VLA, and large areas of alopecia were not present, case 05/377 displayed a positive scratch response, characterised by rhythmical head movements when the dorsum was scratched. A positive scratch response has been associated with teeth grinding and pruritus in classical scrapie [2]; teeth grinding was observed only once in case 05/377 during the observation and thus may not be significant. Case 05/377 was nervous whilst case 06/008 appeared to have a subdued mental status.…”

“…In addition, tremors and loss of weight or bodily condition are frequently displayed. Pruritus resulting in alopecia is most frequently observed, and the "nibble reflex" where sheep respond to scratching of the dorsum with characteristic lip and tongue movements, is often used as a test for pruritus [2]. (See Additional file 1: Movie 1 as an example of a positive scratch test in classical scrapie).…”

Diagnosing limb paresis and paralysis in sheep

“…Paresis and ataxia, especially of the hindlimbs, are common clinical signs (Healy andothers 2003, Jeffrey andGonzalez 2007); quadriplegia and recumbency are seen at a later date. Other clinical signs include separation from the rest of the flock, depression, anxiety or hyperexcitability, head tremor, low head carriage, pruritus (including a 'nibble' response to stimulation of the back), weight loss, bruxism, cud-dropping and an absent menace response (Healy andothers 2003, Konold andPhelan 2014). Most of the sheep that are affected are more than two years of age (Jeffrey and Gonzalez 2007).…”