Validation of Use of Rectoanal Mucosa-Associated Lymphoid Tissue for Immunohistochemical Diagnosis of Chronic Wasting Disease in White-Tailed Deer ( Odocoileus virginianus )

Abstract

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.Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy that has been reported in free-ranging and captive Rocky Mountain elk (Cervus elaphus nelsoni), mule deer (Odocoileus hemionus), white-tailed deer (Odocoileus virginianus), and moose (Alces alces shirasi) in North America (1,23,27,28). Clinical signs of CWD do not appear until very late in the infection process (11), and as the successful management of CWD appears to be dependent on the early detection and elimination of infected individuals (8), a reliable diagnostic test for the identification of infected animals during the early preclinical stage is of paramount importance. Currently, diagnosis is generally dependent on the finding of PrP CWD , the abnormal isoform of the cellular prion protein (PrP C ), in obex and/or lymphoid tissues of animals collected postmortem. Antemortem evaluation of tonsil biopsy specimens has been shown to detect preclinical CWD in deer (17,26,29), but the collection of tonsil tissue is not a universally practical procedure for use in the field, in that it requires general anesthesia and highly trained personnel to collect adequate samples. On the basis of the findings of recent studies that have shown that scrapie-associated PrP (PrP Sc ) is deposited in the rectoanal mucosa-associated lymphoid tis...

Diagnostic accuracy of rectal mucosa biopsy testing for chronic wasting disease within white-tailed deer (Odocoileus virginianus) herds in North America

“…9,11 Thus, the pooled estimate of diagnostic test sensitivity of rectal biopsy testing was 68% when based on the 4 herds of the current study, which was refined to 74% (95% CLs: 60% and 85%) after inclusion of data from 2 additional herds from a similarly conducted study (data not shown). 7 Conversely, false-negative results should be expected from rectal biopsy samples in generally one-fourth of all CWD-infected deer. Thus, a negative test result based on a single rectal biopsy sample should not be interpreted as a deer being free of CWD infection.…”

“…9 The metaanalytic pooled estimates were first computed using only the herds of the current study (n = 4) and then inclusive of data from 2 additional herds (n = 6 total) from a similarly conducted U.S. study. 7 Unless otherwise stated, all meta-analyses converged with satisfaction of the convergence criterion.…”

“…In white-tailed deer, PrP CWD accumulates within multiple lymphoid tissues such as lymph nodes, tonsil, and gut-associated lymphoid tissue during the subclinical phase of disease, prior to the accumulation of PrP CWD within the brain. 7,8 Protease-resistant prion protein in white-tailed deer has a similar tissue distribution to scrapie within sheep and goats, and this wide tissue distribution of abnormal prion protein has been exploited by the utilization of antemortem rectal biopsy testing for the control and eradication of scrapie in Canada since 2006 and in the United States since 2008. [3][4][5] Scrapie diagnostic testing on rectal biopsy samples by the U.S. Department of Agriculture (USDA) is used in specific types of epidemiologic investigations and has been found to be a safe and effective method in live animals.…”

“…3 In white-tailed deer, biopsy samples from palatine tonsil and rectal mucosa have both shown promise as possible antemortem methods to detect CWD. 7,17,20 The rectal biopsy procedure has the advantages of being a simpler and more rapid procedure that can often be performed without sedation. 7 The purpose of the current study was to determine the CWD diagnostic accuracy of immunohistochemical detection of PrP CWD in rectal biopsy samples of white-tailed deer from known positive herds.…”

“…7,17,20 The rectal biopsy procedure has the advantages of being a simpler and more rapid procedure that can often be performed without sedation. 7 The purpose of the current study was to determine the CWD diagnostic accuracy of immunohistochemical detection of PrP CWD in rectal biopsy samples of white-tailed deer from known positive herds. Through a cooperative effort between the Canadian Food Inspection Agency (CFIA) and the USDA, rectal biopsy and other tissue samples were collected from white-tailed deer in 4 herds, each herd depopulated because of a previous diagnosis of CWD.…”