No infectivity detected by direct inoculation of reverse transcriptase-containing concentrates or cocultivation of CHO cells with a battery of cell lines. of the respective species after an infection millions of years ago, the presence of EBV (due to EBV transformation of human B-lymphocytes) or sequences of parvoviruses (e.g. AAV (latent infection leading to integration) due to natural contamination of human embryonic kidney cells and African Green Monkey kidney cells (Hoggan, 1970) , or Procine Parvovirus (latent infection) (Fikrig and Tattersall, 1992 ) (see Section on 'Trypsin')) are due to recent events and can eventually be avoided by using tested cell lines (absence of the respective sequences).