Validation of use of rectoanal mucosa-associated lymphoid tissue for immunohistochemical diagnosis of chronic wasting disease in white-tailed deer (Odocoileus virginianus).

The examination of rectoanal mucosa-associated lymphoid tissue (RAMALT) biopsy specimens for the diagnosis of transmissible spongiform encephalopathies has been described in sheep, elk, and small numbers of mule and white-tailed deer. Previous sample numbers have been too small to validate examination of this type of tissue as a viable antemortem diagnostic test. In this study, we examined RAMALT collected postmortem from 76 white-tailed deer removed from a farm in Wisconsin known to be affected by chronic wasting disease (CWD) and from 210 free-ranging white-tailed deer harvested from an area in Wisconsin where the overall prevalence of CWD among the deer was approximately 4 to 6%. The results of immunohistochemical (IHC) staining of the RAMALT sections were compared to the results of IHC staining of sections from the brain stem at the convergence of the dorsal motor nucleus of the vagus nerve, sections of the medial retropharyngeal lymph nodes (RLNs), and sections of tonsil (sections of tonsil only from captive animals were tested). The sensitivities of the IHC staining test with RAMALT sections were 81% for the captive animals and 91% for the free-ranging animals. False-negative results were usually associated with early infection, indicated by a low intensity of immunostaining in the obex and/or a polymorphism at PRNP codon 96. While the RLN remains the tissue of choice for use for the diagnosis of CWD in white-tailed deer, the results of the present study further support the use of RAMALTs collected antemortem as an adjunct to testing of tonsil biopsy specimens and surveillance by necropsy for the screening of farmed deer which have been put at risk through environmental exposure or exposure to deer with CWD.