Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy affecting captive and free-ranging cervids. Currently, tests for CWD in live animals involve relatively invasive procedures to collect lymphoid tissue biopsies and examine them for CWD-associated, protease-resistant cervid prion protein (PrPCWD) detected by immunohistochemistry (IHC). We adapted an ultrasensitive prion detection system, protein misfolding cyclic amplification (PMCA), to detect PrPCWD in Rocky Mountain elk (Cervus elaphus nelsoni) feces. Our PMCA reproducibly detected a 1.2×107 dilution of PrPCWD (a 10% infected brain homogenate diluted 1.2×106-fold into 10% fecal homogenates), equivalent to approximately 100 pg of PrPCWD/g of feces. We developed a semiquantitative scoring system based on the first PMCA round at which PrPCWD was detected and fit a nonlinear regression curve to our serial dilutions to correlate PMCA scores with known PrPCWD concentrations. We used this PMCA scoring system to detect PrPCWD and estimate its concentration in feces from free-ranging elk from Rocky Mountain National Park, Colorado. We compared our results to PrPCWD IHC of rectoanal mucosa-associated lymphoid tissue and obex from the same animals. The PMCA successfully detected PrPCWD in feces from elk that were positive by IHC, with estimated prion loads from 100 to 5,000 pg PrPCWD/g of feces. These data show for the first time PrPCWD in feces from naturally exposed free-ranging elk and demonstrate the potential of PMCA as a new, noninvasive CWD diagnostic tool to complement IHC.

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