Features
Atypical Scrapie
by Dr Hugh Reid
Through active surveillance for scrapie there has been identification of a condition which has been designated “atypical scrapie”. The significance of this syndrome is as yet unclear. The distribution of lesions and the biochemical characteristics of the altered PrP scrapie-associated protein in the brains of affected animals, does however, appear to be distinct from both that of classical scrapie and experimental cases of BSE in sheep. The vast majority of atypical cases have only been identified in material submitted from aged slaughter animals and very few clinical cases have been diagnosed. Most cases have been found in those sheep that are genetically more resistant to classical scrapie and none have been identified in the genetically most susceptible. However, none of the cases recognised in the genetically most resistant sheep have shown clinical signs.
Transmissibility in the field is unclear. In most flocks where all animals have been examined following identification of an atypical scrapie case, no further affected animals have been identified. It has to be emphasised that “atypical scrapie” has only recently been identified and that much has still to be found out about it. DEFRA has already commissioned VLA to undertake five research projects that should help to clarify some of the uncertainties regarding this condition. From what has already been established there is nothing to suggest that it represents a risk to human health and that the NSP objective of removing those sheep most vulnerable to classical scrapie is still valid.