Current European surveillance regulations for scrapie, a naturally occurring transmissible spongiform encephalopathy (TSE) or prion disease in sheep and goats, require testing of fallen stock or healthy slaughter animals, and outline measures in the case of confirmation of disease. An outbreak of classical scrapie in a herd with 2500 goats led to the culling of the whole herd, providing the opportunity to examine a subset of goats, take samples, and examine them for the presence of disease-associated prion protein (PrP Sc) to provide further information on scrapie test sensitivity, pathology, and association with prion protein genotype. Goats were examined clinically prior to cull, and the brains examined post mortem by Bio-Rad ELISA, a rapid screening test used for active surveillance in sheep and goats, and two confirmatory tests, Western blot and immunohistochemistry. Furthermore, up to 10 lymphoid tissues were examined by immunohistochemistry. Of 151 goats examined, three (2.0%) tested positive for scrapie by ELISA on brain, confirmed by confirmatory tests, and a further five (3.3%) were negative by ELISA but positive by at least one of the confirmatory tests. Only two of these, both positive by ELISA, displayed evident signs of scrapie. In addition, 10 (6.6%) goats, which also included two clinical suspects, were negative on brain examination but had detectable PrP Sc in lymphoid tissue. PrP Sc was detected most frequently in the medial retropharyngeal lymph node (LN; 94.4% of all 18 cases) and palatine tonsil (88.9%). Abnormal behavior and circling or loss of balance when blindfolded were the best clinical discriminators for scrapie status. None of the goats that carried a single allele in the prion protein gene associated with increased resistance to scrapie (Q 211 , K 222 , S 146) were scrapie-positive, and the percentage of goats with these alleles was greater than expected from previous surveys. Significantly more goats that were scrapiepositive were isoleucine homozygous at codon 142 (II 142). The results indicate that the sensitivity of the applied screening test is poor in goats compared to the confirmatory tests as gold standard, particularly for asymptomatic animals. Sensitivity of surveillance could be improved by testing retropharyngeal LN or palatine tonsil in addition to brain.

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The aim of this study was to apply a back-calculation model to Great Britain (GB) classical scrapie surveillance data, and use this model to estimate how many more cases might be expected, and over what time frame these cases might occur. A back-calculation model was applied to scrapie surveillance data between 2005 and 2019 to estimate the annual rate of decline of classical scrapie. This rate was then extrapolated to predict the number of future cases each year going forward. The model shows that there may be yet further cases of classical scrapie in GB. These will most likely occur in the fallen stock scheme, with approximately a 25% probability of at least 1 further scrapie positive, with a very low probability (~0.2%) of having up to three additional scrapie positives. This highlights the difficulty of completely eliminating all further cases, even in the presence of very effective control measures.

Certain genotypes of sheep have been identified to increase their susceptibility (the VRQ allele) or resistance (the ARR allele) to classical scrapie. This study aim was to assess the spatio-temporal pattern of the ARR and VRQ alleles in GB and to explore the risk factors associated to their presence. Data was collected from the GB scrapie surveillance program, the sheep and goat inventory survey (GB census survey) and the agricultural survey for the period 2002-2015. Spatio-temporal trends of genotypes were assessed through the use of choropleth maps, spatial cluster and linear regression analyses. Multivariable mix-effect logistic regression analyses were performed to investigate the association between the resistant or susceptible genotypes, and breeds, farm purpose, animal purpose, surveillance stream, country location and herd size. The results show a significant upward trend in the frequency of most resistant ARR alleles (1.15% per year, 95%CI: 0.76-1.53) and significant downward trend of most susceptible VRQ alleles (-0.40% per year; 95%CI:-0.69 to-0.10]. The trend continue after the termination of the national scrapie control plan in 2009. Breeds such as Herdwick (OR=0,27; 95%CI: 0.15-0.48), Shetland (OR=0.21; 95%CI: 0.12-0.37), Swaledale (OR=0.56; 95%CI: 0.45-0.71), Scottish blackface (OR=0.53; 95%CI: 0.41-0.70) and Welsh Montain (OR: 0.61; 95%CI: 0.45-0.81) were identified with lower odds ratios of having the resistant ARR allele, while Beulah speckled face (OR=1.73; 95%CI: 1.14-2.61), Jacob (OR=2.98; 95%CI: 1.46-6.53), Lleyn (OR=2.91; 95%CI: 1.27-6.66) and Suffolk (OR=2.15; 95%CI: 1.66-2.78) had higher odds ratios of having the ARR allele. Other risk factors associated to presence of ARR allele were finishing farms (OR=1.18; 95%CI:1.06-1.32) and farms in Scotland (OR=0,78; 95%CI: 0.74-0.84) and in Lowland grazing areas (OR=1.52; 95%CI: 1.39-1.67). Risk factors associated with presence the VRQ genotype were farms in Scotland (OR=0,85; 95%CI: 0.77-0.93) and breeds such as Herdwick (OR=2.05; 95%CI: 1.02-4.14), Shetland (OR=4.29; 95%CI: 2.31-7.28) and Sweledale (OR=1.53; 95%CI: 1.11-2.10). For the most resistant genotype, two significant spatial clusters were identified: a high-risk cluster in the southwest of GB (RR=1.51, p<0.001) and a low-risk cluster in northern GB (RR=0.65, p<0.001). For the most susceptible genotypes, one significant high-risk cluster was identified in Wales (RR = 2.89 and p=0.013).

Multiple controls established during the bovine spongiform encephalopathy (BSE) epidemic were not solely applied to BSE in cattle, but were implemented for scrapie in sheep and goats due to concerns over the occurrence of BSE in sheep. In the absence of BSE in sheep being observed, control measures for prion diseases are now being evaluated to ensure they remain proportionate to risk. This risk assessment, aims to estimate, by use of stochastic simulation, the impact of reducing controls for Specified Risk Materials (SRM) from sheep at abattoir. Three scenarios have been included: 1) current list of SRM; 2) brain and spinal cord of adult sheep; and 3) the brain of adult sheep. Results indicate the total amount of infectivity passing through British abattoirs is highest for atypical scrapie with nearly 3,500,000 Ovine Oral (OO) ID per year. The majority of this infectivity enters Category 1 waste for incineration, with only 13,000 OO ID per year within edible products. Under Scenario 2, an additional 4000 OO ID per year would be classified as edible products from the lifting of restrictions on the distal ileum of adult sheep. However, if SRM removal was limited to brain, an additional 110,000 OO ID per year would be permitted into edible products with the lifting of restrictions on the spinal cord of adult sheep. For classical scrapie, there is a mean estimate of infectivity of 30,000 OO ID per year at abattoir. This is lower than for atypical scrapie due to the lower occurrence of this disease in Great Britain. However, more infectivity is destined to reach the food chain as the disease is peripherally distributed in the carcase. The highest contributor to the total amount of infectivity consumed per year is the intestines (duodenum and jejunum). If SRM removal is limited to the brain and spinal cord of sheep over 12 months of age, there is an approximate mean increase from 19,000 to 21,000 OO ID per year diverted to edible products. If the SRM list is restricted to brain only, this increases to over 23,000 OO ID per year. For the potential of sheep-BSE, there is a very low estimate of 29 OO ID per year in total from carcases entering abattoir, due to the potential very rare occurrence of this disease. Given changes in SRM regulations there is a change of an additional 4 OO ID per year being diverted to edible products.