Submitted to: Veterinary Record
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/16/2003
Publication Date: 9/24/2004
Citation: Spraker, T.R., Balachandran, A., Zhuang, D., O'Rourke, K.I. 2004. Variable patterns of distribution of PrP(CWD) in the obex and cranial lymphoid tissues of Rocky Mountain elk (Cervus elaphus nelsoni) with subclinical chronic wasting disease. Veterinary Record. 155(10):295-302. Interpretive Summary: Chronic wasting disease is a fatal brain disorder of captive and free ranging deer and elk. Surveillance and diagnosis are based on identification of a marker protein in tissues from infected animals. The accuracy of the testing is based on an understanding of the precise location of the marker protein deposits in various tissues of infected animals. In this study, a large population of elk with the disease was examined by microscopic, genetic, and biochemical assays. The marker protein distribution was variable and no single tissue was found to be adequate for correct diagnosis. Elk genetics, the route of exposure, and/or the agent strain may account for this variation.
Technical Abstract: Chronic wasting disease is a member of the transmissible spongiform encephalopathies, a heterogeneous group of fatal neurodegenerative disorders. The disease affects captive and free ranging mule deer, white tailed deer, and elk in some areas of the US and Canada. Extensive control measures in captive elk are based on diagnosis of the disease through testing of clinical suspects and depopulation of herds with potential exposure to the disease. Diagnostic testing is based on examination of one or more tissues selected by comparison to similar diseases of sheep and mule deer. In this study, a sample for more than 10,000 elk from depopulated herds was examined by immunohistochemistry assay of medulla at the level of the obex, palatine tonsil and medial retropharyngeal lymph node. Confirmatory western blot analysis and DNA sequence analysis of the PRNP gene were performed on positive cases. The study demonstrated that while the medulla at the level of the obex is the most suitable section of brain for early diagnosis, addition of the medial retropharyngeal lymph node improves the accuracy of diagnosis. In contrast to diagnostic testing of mule deer or white tailed deer, however, examination of the retropharyngeal node alone is insufficient for diagnosis in more than 12% of the cases. The study will be useful in design of cost-effect surveillance and diagnostic programs in the US and Canada.