A paired case-control study of risk factors for scrapie in Irish sheep flocks.

We did a case-control study of the association of several animal, flock and management factors with scrapie in Irish sheep flocks. The characteristics of 61 sheep flocks with at least one laboratory-confirmed case of scrapie (1990-1998) were compared to 61 flocks with no history of scrapie and matched by geographical location and attending veterinary surgeon. The 61 scrapie-affected flocks were from the database of known scrapie flocks in the Republic of Ireland at the start of the study. In conditional multiple logistic regression, factors associated with increased odds of scrapie in a sheep flock were (i) larger breeding-flock size, (ii) purchasing replacement sheep through the market, (iii) spreading sheep compost on the land and (iv) disposing of the placenta in the compost. Factors associated with decreased odds of scrapie were (i) using cattle slurry on the land and (ii) feeding proprietary concentrates to lambs.

The clinical neurology of scrapie in Irish sheep.

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) < 1.5 (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 < .0005) with prion protein (PrP) genotypes AA136RR154QH171 and AA136RR154QQ171. 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.