Analysis of risk to biomedical products developed from animal sources (with special emphasis on the spongiform encephalopathy agents, scrapie and BSE).

Factors that must be considered in estimations of risk from exposure to adventitious contaminants of animal derived biologicals include: (i) the use of the product; (ii) the routes of administration and exposure to potential pathogens; (iii) the source of animal(s) and their history and maintenance; (iv) the tissue(s) used in the product and their likelihood of harbouring or being contaminated by an agent; (v) the methods by which the animal is slaughtered and the tissue(s) collected; (vi) the production process including steps that remove an agent either by inactivation or physical separation; (vii) the disposal of an agent that is sequestered but not inactivated; (viii) flow control, barriers, and between-batch cleaning; (ix) batch size; and (x) validations and quality assurance monitoring. The transmissible spongiform encephalopathy (TSE) agents, scrapie and bovine spongiform encephalopathy (BSE) are among the most difficult to detect and remove from animal tissues. As such they constitute an especially stringent challenge for viral clearance.