sPMCA analysis of dust samples. Example sPMCA western blot from dust samples taken from four surfaces (Area 1, 2, 3 and 4), inaccessible to direct contact with sheep, within a scrapie-affected barn were extracted and subject to sPMCA. Control sample 1: represent 6 individual reactions amplifying negative control extracts taken from a scrapie-free barn. PrPSc was detected using monoclonal antibody SHa31; M are 20 and 30 kDa molecular mass markers. In total 15/30 reactions from the scrapie affected farm were sPMCA positive, whilst 1/18 from the negative samples amplified, and presumed a false positive result.