Infectivity of heat-treated BSE homogenate remains after PrPSc removal with keratinase. Infectivity diagnosis was based on PrPSc tests in Tgbov XV mice. Symbols: squares and circles represent respectively non-digested and KE-digested material, triangles the end point titration data of homogenate without detergent/heat pretreatment. Solid lines, data from 1st experiment; broken lines data from 2nd experiment. The data can be found in the Additional file 3.