Passage of chronic wasting disease prion into transgenic mice expressing Rocky Mountain elk (Cervus elaphus nelsoni) PrPC

Chronic wasting disease (CWD) of elk (Cervus elaphus nelsoni) and mule deer (Odocoileus hemionus) is one of three naturally occurring forms of prion disease, the others being Creutzfeldt-Jakolo disease in humans and scrapie in sheep. In the last few decades, CWD has spread among captive and free-ranging cervids in 13 US states, two Canadian provinces and recently in Korea. The origin of the CWD agent(s) in cervids is not known. This study describes the development of a transgenic mouse line (TgElk) homozygous for a transgene array encoding the elk prion protein (PrPC) and its use in propagating and simulating CWD in mice. Intracerebral injection of one mule deer and three elk CWD isolates into TgElk mice led to disease with incubation periods of 127 and 95 days, respectively. Upon secondary passage, the incubation time was reduced to 108 and 90 days, respectively. Upon passage into TgElk mice, CWD prions (PrPSc) maintained the characteristic Western blot profiles seen in CWD-affected mule deer and elk and produced histopathological modifications consistent with those observed in the natural disease. The short incubation time observed on passage from cervid to mouse with both mule deer and elk CWD brain homogenates and the demonstrated capacity of the animals to propagate (mouse to mouse) CWD agents make the TgElk line a valuable model to study CWD agents in cervid populations. In addition, these results with this new transgenic line suggest the intriguing hypothesis that there could be more than one strain of CWD agent in cervids.