TSE eradication in small ruminants--quo vadis?

The term of 'TSE infections in small ruminants' summarises BSE as well as classical and the recently discovered atypical scrapie infections in sheep and goats. There are fundamental differences between the TSE infections in small and large ruminants. Other than in bovines the TSE pathogenesis in small ruminants implies that various peripheral tissues become infectious long before the onset of clinical symptoms. At least in sheep, classical scrapie is efficiently transmitted horizontally within affected flocks. On the other hand, BSE poses a distinctly higher zoonotic risk than scrapie. Therefore, regulatory measures for the protection of animals and humans from a BSE infection must be substantially different for large and small ruminants. While culling of the birth and feeding cohort of a BSE affected cattle is considered to be effective to prevent any further BSE cases in the affected herd, an effective BSE and classical scrapie eradication programme in small ruminants requires a much more stringent eradication strategy and the rendering of all susceptible animals. The situation became even more complicated when atypical scrapie cases with divergent transmission and pathogenesis characteristics and with a novel biochemical phenotype of the infectious agent came into play. The discovery of these atypical scrapie cases has initiated a discussion about the suitability of the current TSE eradication measures in sheep (which are selective breeding and genotype based culling), in particular when such cases were also found in sheep carrying the believed scrapie resistant genotypes.