SPONGIFORM ENCEPHALOPATHY IN FREE-RANGING MULE DEER (ODOCOILEUS-HEMIONUS), WHITE-TAILED DEER (ODOCOILEUS-VIRGINIANUS) AND ROCKY-MOUNTAIN ELK (CERVUS-ELAPHUS-NELSONI) IN NORTHCENTRAL COLORADO

Between March 1981 and June 1995, a neurological disease characterized histologically by spongiform encephalopathy was diagnosed in 49 free- ranging cervids from northcentral Colorado (USA). Mule deer (Odocoileu s hemionus) were the primary species affected and accounted for 41 (84 %) of the 49 cases, but six Rocky Mountain elk (Cervus elaphus nelsoni ) and two white-tailed deer (Odocoileus virginianus) were also affecte d. Clinical signs included emaciation, excessive salivation, behaviora l changes, ataxia, and weakness. Emaciation with total loss of subcuta neous and abdominal adipose tissue and serous atrophy of remaining fat depots were the only consistent gross findings. Spongiform encephalop athy characterized by microcavitation of gray matter, intraneuronal va cuolation and neuronal degeneration was observed microscopically in al l cases. Scrapie-associated prion protein or an antigenically indistin guishable protein was demonstrated in brains from 26 affected animals, 10 using an immunohistochemical staining procedure, nine using electr on microscopy, and seven using Western blot. Clinical signs, gross and microscopic lesions and ancillary test findings in affected deer and elk were indistinguishable from those reported in chronic wasting dise ase of captive cervids. Prevalence estimates, transmissibility, host r ange, distribution, origins, and management implications of spongiform encephalopathy in free-ranging deer and elk remain undetermined.