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Antemortem detection of PrPCWD in preclinical, ranch-raised Rocky Mountain elk (Cervus elaphus nelsoni) by biopsy of the rectal

Posted Jan 14 2009 4:55pm
Full Scientific Reports

Antemortem detection of PrPCWD in preclinical, ranch-raised Rocky Mountain elk (Cervus elaphus nelsoni) by biopsy of the rectal mucosa

Terry R. Spraker, Kurt C. VerCauteren, Thomas Gidlewski, David A. Schneider, Randy Munger, Aru Balachandran and Katherine I. O'Rourke1 Correspondence: 1Corresponding Author: Katherine O'Rourke, USDA, ARS ADRU, 3003 ADBF, Pullman, WA 99164. katherine.o'

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 PrPCWD, the protein marker for CWD infection, by immunohistochemistry. PrPCWD 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. PrPCWD 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.

Key Words: Antemortem diagnosis • chronic wasting disease • elk • transmissible spongiform encephalopathy

Brief Research Reports

Field performance of two rapid screening tests in active surveillance of transmissible spongiform encephalopathies in small ruminants

Torsten Seuberlich1, Marcus G. Doherr, Catherine Botteron, Alexandra Nicolier, Heinzpeter Schwermer, Hervé Brünisholz, Dagmar Heim and Andreas Zurbriggen Correspondence: 1Corresponding Author: Torsten Seuberlich, NeuroCentre, Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Berne, Bremgartenstrasse 109 a, CH-3001 Berne, Switzerland.

Recently, screening tests for monitoring the prevalence of transmissible spongiform encephalopathies specifically in sheep and goats became available. Although most countries require comprehensive test validation prior to approval, little is known about their performance under normal operating conditions. Switzerland was one of the first countries to implement 2 of these tests, an enzyme-linked immunosorbent assay (ELISA) and a Western blot, in a 1-year active surveillance program. Slaughtered animals (n = 32,777) were analyzed in either of the 2 tests with immunohistochemistry for confirmation of initial reactive results, and fallen stock samples (n = 3,193) were subjected to both screening tests and immunohistochemistry in parallel. Initial reactive and false-positive rates were recorded over time. Both tests revealed an excellent diagnostic specificity (>99.5%). However, initial reactive rates were elevated at the beginning of the program but dropped to levels below 1% with routine and enhanced staff training. Only those in the ELISA increased again in the second half of the program and correlated with the degree of tissue autolysis in the fallen stock samples. It is noteworthy that the Western blot missed 1 of the 3 atypical scrapie cases in the fallen stock, indicating potential differences in the diagnostic sensitivities between the 2 screening tests. However, an estimation of the diagnostic sensitivity for both tests on field samples remained difficult due to the low disease prevalence. Taken together, these results highlight the importance of staff training, sample quality, and interlaboratory comparison trials when such screening tests are implemented in the field.

Key Words: Goats • prion • rapid tests • scrapie • sheep • surveillance • transmissible spongiform encephalopathy

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Terry S. Singeltary Sr.
P.O. Box 42
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