PRNP and scrapie: Whilst the zoonotic potential of BSE has been unequivocally confirmed through transmission into transgenic mice expressing bovine, chimeric or human sequences [6, 64, 164], a number of studies using various different mouse models overexpressing human PrP on the background of Prnp0/0 mice have demonstrated lack of such a potential for scrapie and CWD [96, 149, 159, 170].