Immunohistochemical diagnosis of chronic wasting disease in preclinically affected elk from a captive herd

An immunohistochemical (IHC) method was used to test brain tissues from 17 elk in a captive herd in which chronic wasting disease (CWD) had previously occurred. The IHC technique detects the protease-resistant prion protein ( PrP-res), which is considered a disease specific marker for transmissible s pongiform encephalopathies (TSE), regardless of the species affected. Of th e 17 elk tested, 10 were positive by IHC. Only 2 of these 10 animals had sh own clinical signs and histologic lesions of CWD, and an additional animal had histologic lesions only. The most consistently IHC-positive tissue was medulla oblongata, especially the obex. These results show that the PrP-res MC test on brain tissue, specifically medulla oblongata at the obex, shoul d be considered an essential component of any surveillance study intended t o determine the incidence of CWD in captive or free-ranging cervids.