PRNP and prion disease: In tissues from some animals, a low level of PrP converting activity was observed with RT-QuIC and PMCA assays and sub-passage in mice overexpressing elk PrP (TgElk) or deer PrP (Tg1536) gave low attack rates, but subsequent passage from 2nd passage in mice, to bank voles resulted in 100% attack rates and appearance of typical prion disease pathology.