Scrapie: the risk of its introduction and effects on trade.

New Zealand and Australia are fortunate in that they are among the few sheep rearing countries free from scrapie, despite cases in imported sheep in the 1950s. The importance of sheep rearing in the Australasian economies, and the difficulties involved in importing sheep without risking the introduction of scrapie, has meant that there have been very few importations of new blood lines in the last 40 years, and those that have been imported have been through stringent programs designed to ensure freedom from scrapie. While scrapie can be a cause of significant wastage in some sheep rearing situations, its major threat to Australasia is probably to the developing biopharmaceutical industries which, since the emergence of bovine spongiform encephalopathy, have benefitted from an international demand for products guaranteed to be derived from livestock free from the transmissible spongiform encephalopathies. This paper outlines one method which has been used to assess the risk of introducing scrapie as the result of importation of sheep and discusses the difficulty in ascertaining what constitutes an acceptable risk.