Classical and Atypical Scrapie in Sheep and Goats. Review on the Etiology, Genetic Factors, Pathogenesis, Diagnosis, and Control Measures of Both Diseases

SIMPLE SUMMARY: Classical scrapie is a prionic, neurological, consumptive, and chronic disease that affects naturally domestic small ruminants. It was initially described in the UK, and since then it has spread throughout the world. Atypical scrapie was first diagnosed in Norway in the 1990s, being diagnosed throughout the world since then. Here, we a provide review of scrapie disease, deepening the characteristics of the causal agent, the pathogenesis of the disease, and its transmission mechanisms. We also emphasize the role of genetic factors, the diagnostic techniques, and the surveillance and control methods established in the European Union. Finally, the infectivity of the different tissues is described. ABSTRACT: Prion diseases, such as scrapie, are neurodegenerative diseases with a fatal outcome, caused by a conformational change of the cellular prion protein (PrP(C)), originating with the pathogenic form (PrP(Sc)). Classical scrapie in small ruminants is the paradigm of prion diseases, as it was the first transmissible spongiform encephalopathy (TSE) described and is the most studied. It is necessary to understand the etiological properties, the relevance of the transmission pathways, the infectivity of the tissues, and how we can improve the detection of the prion protein to encourage detection of the disease. The aim of this review is to perform an overview of classical and atypical scrapie disease in sheep and goats, detailing those special issues of the disease, such as genetic factors, diagnostic procedures, and surveillance approaches carried out in the European Union with the objective of controlling the dissemination of scrapie disease.