U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version



Veterinary Pathology 2023, Vol. 60(4) 420– 433



U.S. government work


Chronic wasting disease (CWD) is an infectious transmissible spongiform encephalopathy of cervids associated with the presence of a misfolded prion protein (PrPCWD). Progression of PrPCWD distribution has been described using immunohistochemistry and histologic changes in a single section of brain stem at the level of the obex resulting in scores from 0 (early) to 10 (terminal) in elk with naturally occurring CWD. Here we describe the spread and distribution of PrPCWD in peripheral tissues and spinal cord in 16 wild and 17 farmed Rocky Mountain elk (Cervus elaphus nelsoni) with naturally occurring CWD and correlate these findings with obex scores. Spinal cord and approximately 110 peripheral tissues were collected, processed, stained with hematoxylin and eosin, and immunolabeled with the anti-prion protein monoclonal antibody F99/97.6.1. The medial retropharyngeal and tracheobronchial lymph nodes were the first tissues to accumulate PrPCWD, followed by other lymphoid tissues, myenteric plexus, spinal cord, and finally tissues outside of the lymphatic and neural systems. However, the only significant histological lesion observed was mild spongiform encephalopathy in the dorsal column of the lower spinal cord in elk with an obex score of ≥9. Initial exposure to CWD prions may be through the respiratory system and spread appears to occur primarily via the autonomic nervous system. Therefore, we suggest using obex scores as a proxy for stage of disease progression and verifying with key peripheral tissues.