Wildlife Disease and Zoonotics


Date of this Version



Published in Veterinary Pathology 47(3) 536-546 (2010)


Eyes and nuclei of the visual pathways in the brain were examined in 30 Rocky Mountain elk (Cervus elaphus nelsoni) representing 3 genotypes of the prion protein gene PRNP (codon 132: MM, ML, or LL). Tissues were examined for the presence of the abnormal isoform of the prion protein associated with chronic wasting disease (PrPCWD). Nuclei and axonal tracts from a single section of brain stem at the level of the dorsal motor nucleus of the vagus nerve were scored for intensity and distribution of PrPCWD immunoreactivity and degree of spongiform degeneration. This obex scoring ranged from 0 (elk with no PrPCWD in the brain stem) to 10 (representing elk in terminal stage of disease). PrPCWD was detected in the retina of 16 of 18 (89%) elk with an obex score of > 7. PrPCWD was not detected in the retina of the 3 chronic wasting disease–negative elk and 9 elk with an obex score of < 6. PrPCWD was found in the nuclei of the visual pathways in the brain before it was found in the retina. Within the retina, PrPCWD was first found in the inner plexiform layer, followed by the outer plexiform layer. Intracytoplasmic accumulation of PrPCWD was found in a few neurons in the ganglion cell layer in the PRNP 132ML elk but was a prominent feature in the PRNP 132LL elk. Small aggregates of PrPCWD were present on the inner surface of the outer limiting membrane in PRNP 132LL elk but not in PRNP 132MM or 132ML elk. This study demonstrates PrPCWD accumulation in nuclei of the visual pathways of the brain, followed by PrPCWD in the retina.