Other precautions: The screening of animal derived raw materials for the presence of adventitious viruses is of utmost importance, however, as already mentioned, screening has its limits, because it is impractical to screen for all theoretical viruses, and other new viruses might emerge for which no tests are available. Because of this supplementary precautions have to be undertaken for reducing the risk of viral contamination, by inactivating or eliminating at least viruses of families, which are susceptible for inactivation and/or elimination. With respect to the treatment of fetal bovine serum for animal cell technology, γ irradition, and UVC irradiation are used. Heat treatment as well as treatment with peracetic acid are possible, however, they are not really used.