Bovine spongiform encephalopathy (BSE) and its potential to affect humans emerged as a concern in the 1990s. So suppliers of many essential animal-sourced components used in cell culture and fermentation processes became concerned about the potential for material contamination with prions. Viruses also can be present in raw materials derived from animal origins. Many important drug and vaccine products are made by mammalian cell culture or bacterial fermentation, so their biological safety is paramount. However, it is very difficult to…