Antemortem Detection of PrP^CWD in Preclinical, Ranch-Raised Rocky Mountain Elk (Cevvus Elaphus Nelsoni) by Biopsy of the Rectal Mucosa

Abstract

Abstract. Antemortem biopsy of the rectal mucosa was evaluated as a method for the preclinical diagnosis of chronic wasting disease (CWD) in a herd of ranch-raised Rocky Mountain elk (Cervus elaphus nelsoni) quarantined because of exposure to CWD. Biopsy samples were obtained from 41 elk during the winter of [2005][2006] and from 26 elk from that herd still alive and available for testing during the winter of 2006-2007. Samples were examined for PrP CWD , the protein marker for CWD infection, by immunohistochemistry. PrP CWD was detected in follicles of the rectoanal mucosa-associated lymphoid tissue in biopsy samples from 1 elk with clinical signs of chronic wasting disease and 5 clinically normal elk. The diagnosis was confirmed in all 6 animals by postmortem analysis of brain and peripheral lymph nodes. PrP CWD was also observed in the submucosal plexus and myenteric plexus of the enteric nervous system, and in close association with nonmyelinated mucosal and submucosal nerve fibers. In antemortem rectal biopsy samples from positive animals, immunostaining was consistently observed in approximately 60% of the mucosa-associated lymphoid tissue follicles if 10 or more total follicles per biopsy were present for evaluation. Most antemortem biopsy samples obtained from elk younger than 6.5 years contained at least 10 follicles per rectal mucosal biopsy. These findings support the analysis of antemortem biopsy of the rectal mucosa samples as part of an integrated strategy to manage chronic wasting disease in Rocky Mountain elk.

Impact of Age and Sex of Rocky Mountain Elk (Cervus Elaphus Nelsoni) on Follicle Counts from Rectal Mucosal Biopsies for Preclinical Detection of Chronic Wasting Disease

“…As previously acknowledged, the minimum number of lymphoid follicles needed for an accurate diagnosis of CWD using rectal mucosal biopsies in elk is unknown but is estimated to be 10 follicles. 9 Although this question was not addressed in the current study, a minimum of 10 follicles indicates that it may be more difficult to acquire enough follicles from elk that are .8.5 years of age. However, the follicle numbers obtained in the present study were adequate to detect PrP CWD in 8 nonclinical elk that were ,8 years of age.…”

“…The use of rectal mucosal biopsies has also been reported 9 in a herd of 40 ranch-raised elk, and 5 nonclinical cases of CWD were found with PrP CWD in lymphoid follicles of rectal mucosal. Both of these studies 8,9 indicate that rectal biopsies may be a useful technique for diagnosing preclinical CWD in elk, but they also indicate potential limitations. The lymphoid tissues may not be affected in all elk with PrP CWD , and PrP CWD may not be present in lymphoid follicles of rectal mucosae in extremely early cases.…”

“…A limitation of using lymphoid tissue from the rectal mucosal biopsy technique in elk appears to be a decrease in the number of follicles as elk age. 6,9 If the number of follicles decreases too much, then the test would decrease in sensitivity and be of limited use in older animals. As previously acknowledged, the minimum number of lymphoid follicles needed for an accurate diagnosis of CWD using rectal mucosal biopsies in elk is unknown but is estimated to be 10 follicles.…”

“…Preclinical diagnostic tests for CWD have been described for mule deer using biopsy tissues of palatine tonsil 10 and rectal mucosa. 13 A rectal mucosal biopsy technique has recently been described 6,9 for detecting CWD in Rocky Mountain elk. Examination of postmortem rectal mucosal tissue sections for evidence of the prion protein associated with CWD (PrP CWD ) has been reported 8 in elk for diagnosis of CWD, and data indicate that the technique may be useful in the diagnosis of preclinical cases of CWD.…”

“…The technique used for taking the biopsies has been previously described. 9 Biopsies were taken by 4 of the authors (RDM, TLG, KCV, TRS) and 3 veterinarians that were trained on the technique by the authors. Rectal biopsies were fixed in formalin solution, processed routinely, and embedded in paraffin.…”