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Title: Progressive accumulation of the abnormal conformer of the prion protein and spongiform encephalopathy in the obex of nonsymptomatic and symptomatic Rocky Mountain elk (Cervus elaphus nelsoni) with chronic wasting disease

Author
item SPRAKER, TERRY - Colorado State University
item GIDLEWSKI, T - Animal And Plant Health Inspection Service (APHIS)
item POWERS, J - National Park Service
item NICHOLS, T - Animal And Plant Health Inspection Service (APHIS)
item BALACHANDRAN, ARU - Canadian Food Inspection Agency
item CUMMINS, B - Colorado State University
item WILD, M - National Park Service
item VERCAUTEREN, K - Animal And Plant Health Inspection Service (APHIS)
item O'Rourke, Katherine

Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2015
Publication Date: 7/16/2015
Citation: Spraker, T.R., Gidlewski, T., Powers, J.G., Nichols, T., Balachandran, A., Cummins, B., Wild, M.A., Vercauteren, K., O'Rourke, K. 2015. Progressive accumulation of the abnormal conformer of the prion protein and spongiform encephalopathy in the obex of nonsymptomatic and symptomatic Rocky Mountain elk (Cervus elaphus nelsoni) with chronic wasting disease. Journal of Veterinary Diagnostic Investigation. doi: 10.117/1040638715593368.

Interpretive Summary: Chronic wasting disease is a fatal brain disorder of deer and elk. The disease is associated with accumulation of a misfolded protein, the prion protein or PrP-CWD. The disease course is prolonged and elk may harbor the agent for 2 to 6 years before showing clinical signs. The potential for spread of the disease from elk in this preclinical period is not well understood. In this study, a detailed examination of the brain and peripheral tissues of elk was performed to determine the location, extent, and abundance of misfolded prion proteins. A system for assigning a numerical score to the brain in each animal was developed. Higher scores were assumed to reflect increasing disease severity. The spread of the infectious agent through the tissues of the body, including sites with potential for shedding into the environment and transmitting disease, was compared to the brain score. Based on the findings, predictions of the length of time an elk has been infected and the potential for spread of the disease can be made from examination of a single slice of brain. This method may be useful in evaluating the potential for transmission from infected elk, particularly those moved from one farm to another during the preclinical period.

Technical Abstract: Chronic wasting disease (CWD), a transmissible spongiform encephalopathy, has been reported in captive and free-ranging cervids. An abnormal isoform of a prion protein (PrP-CWD) has been associated with CWD in Rocky Mountain elk (Cervus elaphus nelsoni) and this prion protein can be detected with immunohistochemistry. Although prion proteins in the brain are associated with clinical disease, abnormal prions in the peripheral tissues are probably associated with transmission at undetermined times during the prolonged incubation period. Regulatory personnel are charged with estimating the risk to other elk in the herd and in the herd of origin for purchased elk. However, samples from field submissions frequently include only the medulla at the level of the obex. In order to determine whether the presumed incubation time and transmission potential can be estimated from this sample, a detailed scoring technique of the obex was formulated and applied to the obex score in elk experimentally infected with the CWD agent with known incubation times. If the time course of the natural disease is similar to that of experimentally infected elk, the scoring may aid in estimating the length of time that an elk with naturally occurring CWD had been incubating the CWD agent. Further, if the kinetics of prion accumulation in the peripheral tissues follows a similar progression in experimental and natural cases, correlation between the obex score and distribution of the agent in the peripheral tissues might be useful in predicting the transmission potential of elk at different stages of disease.