Progressive accumulation of the abnormal conformer of the prion protein and spongiform encephalopathy in the obex of nonsymptomatic and symptomatic Rocky Mountain elk (Cervus elaphus nelsoni) with chronic wasting disease

The purpose of our study was to describe the progressive accumulation of the abnormal conformer of the prion protein (PrPCWD) and spongiform degeneration in a single section of brain stem in Rocky Mountain elk ( Cervus elaphus nelsoni) with chronic wasting disease (CWD). A section of obex from 85 CWD-positive elk was scored using the presence and abundance of PrPCWD immunoreactivity and spongiform degeneration in 10 nuclear regions and the presence and abundance of PrPCWD in 10 axonal tracts, the subependymal area of the fourth ventricle, and the thin subpial astrocytic layer (glial limitans). Data was placed in a formula to generate an overall obex score. Data suggests that PrPCWD immunoreactivity and spongiform degeneration has a unique and relatively consistent pattern of progression throughout a section of obex. This scoring technique utilizing a single section of obex may prove useful in future work for estimating the presence and abundance of PrPCWD in peripheral tissues and the nervous system in elk with CWD.