Assessment of Palatine Tonsil Testing by ELISA for Chronic Wasting Disease Detection in Free-Ranging Mule Deer (Odocoileus hemionus)

Chronic wasting disease (CWD) is a fatal transmissible spongiform encephalopathy affecting cervids. Transmission occurs through oral and nasal mucosal exposure to infectious prions (PrP^CWD), causing cellular prion proteins (PrP^C) to misfold. Currently, the approved diagnostic assays for CWD are immunohistochemistry (IHC) and ELISA. While IHC is considered the gold standard, ELISA is used by most diagnostic laboratories as a screening test for free-ranging cervids. Currently, two tissues have been validated for use with the cervid ELISA test: the medial retropharyngeal lymph node (MRPLN) and the obex region of the brainstem. Palatine tonsil has not been validated for use with the ELISA despite trafficking of PrP^CWD to the tonsils early in the course of disease in deer. Here we assessed the suitability of palatine tonsil for CWD testing of free-ranging mule deer (Odocoileus hemionus) using two commercially available ELISA kits in conjunction with IHC. We tested paired MRPLN and tonsillar tissues, collected from hunter-harvested and non-hunter-harvested mule deer (n=176) in Wyoming, US, from 2020 to 2024. Our findings indicated 100% agreement between MRPLN and palatine tonsil, with no difference in the performance of the two commercially available ELISA kits, confirming that palatine tonsil can be substituted for MRPLN for CWD surveillance in free-ranging mule deer with high confidence.