PRNP and variant Creutzfeldt-Jakob disease: On second passage performed with brain homogenate from a PrPres-negative mouse (succumbed at 576 dpi) from the first passage (BSE2 isolate), 3 out of 4 inoculated tg340 mice tested positive for brain PrPres by western blot with a survival time of 572±37 d.p.i. It is important to note that all the cattle BSE isolates tested in this study were transmitted as efficiently as vCJD isolates or other BSE-related sources to bovine PrP transgenic mice (Table 2 and 3), thus suggesting that they may have a comparable infectivity in the absence of an apparent transmission barrier [36].