Case-control study on the use of pituitary-derived hormones from sheep as a potential risk factor for the occurrence of atypical scrapie in Great Britain

MRI changes observed in a case of atypical scrapie in a 7-year-old Herdwick ewe

Atypical scrapie is a transmissible spongiform encephalopathy that is rarely diagnosed in living animals. In March 2022, a 7-y-old Herdwick ewe was referred to the Scottish Centre for Production Animal Health and Food Safety because of circling behavior and ill thrift. The ewe had a low body condition score, was obtunded, with a wide-based stance of the pelvic limbs, and was circling to the left. Hematologic, biochemical, and CSF analyses were unremarkable, but postmortem magnetic resonance imaging (MRI) findings were consistent with diffuse, bilateral, and symmetrical atrophy of the forebrain and ventriculomegaly. The clinical signs, the involvement of an individual older ewe, and the MRI results led to the clinical diagnosis of scrapie. Immunohistochemistry on the fixed brain, performed by the U.K. Animal and Plant Health Agency, revealed deposits of PrPSc, which is a specific disease marker of transmissible spongiform encephalopathies, mainly in the cerebellum and at lower concentrations in the cerebrum and obex, consistent with the diagnosis of atypical scrapie. MRI findings in a sheep with atypical scrapie have not been described previously, to our knowledge. Scrapie should be included in the list of clinical differential diagnoses when veterinarians are presented with sheep with progressive neurologic signs of several weeks' duration.

Scientific report on the analysis of the 2-year compulsory intensified monitoring of atypical scrapie

The European Commission asked EFSA whether the scientific data on the 2-year intensified monitoring in atypical scrapie (AS) outbreaks (2013-2020) provide any evidence on the contagiousness of AS, and whether they added any new knowledge on the epidemiology of AS. An ad hoc data set from intensified monitoring in 22 countries with index case/s of AS in sheep and/or goats (742 flocks from 20 countries, 76 herds from 11 countries) was analysed. No secondary cases were confirmed in goat herds, while 35 secondary cases were confirmed in 28 sheep flocks from eight countries. The results of the calculated design prevalence and of a model simulation indicated that the intensified monitoring had limited ability to detect AS, with no difference between countries with or without secondary cases. A regression model showed an increased, but not statistically significant, prevalence (adjusted by surveillance stream) of secondary cases in infected flocks compared with that of index cases in the non-infected flocks (general population). A simulation model of within-flock transmission, comparing a contagious (i.e. transmissible between animals under natural conditions) with a non-contagious scenario, produced a better fit of the observed data with the non-contagious scenario, in which each sheep in a flock had the same probability of developing AS in the first year of life. Based on the analyses performed, and considering uncertainties and data limitations, it was concluded that there is no new evidence that AS can be transmitted between animals under natural conditions, and it is considered more likely (subjective probability range 50-66%) that AS is a non-contagious, rather than a contagious disease. The analysis of the data of the EU intensified monitoring in atypical scrapie infected flocks/herds confirmed some of the known epidemiological features of AS but identified that major knowledge gaps still remain.