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In the past 12 years (1967-79) a syndrome we identify as chronic wasting disease has been observed in 53 mule deer (Odocoileus hemionus hemionus) and one black-tailed deer (Odocoileus hemionus columbianus) held in captivity in several wildlife facilities in Colorado and more recently in Wyoming. Clinical signs were seen in adult deer and included behavioral alterations, progressive weight loss and death in 2 weeks to 8 months. Gross necropsy findings included emaciation and excess rumen fluid admixed with sand and gravel. Consistent histopathologic change was limited to the central nervous system and characterized by widespread spongiform transformation of the neuropil, single or multiple intracytoplasmic vacuoles in neuronalperikaryons and intense astrocytic hypertrophy and hyperplasia. Presented is a clinical characterization of chronic wasting disease and pathologic evidence supporting the conclusion that the disease is a specific spontaneously occurring form of spongiform encephalopathy. mouflon (Ovis musimon).

The known host range of naturally-occurring transmissible spongiform encephalopathies has expanded in recent years to include wild ruminants. Chronic wasting disease (CWD) occurs in mule deer (Odocoileus hemionus hemionus) and Rocky Mountain elk (Cervus elaphus nelsoni) in Colorado and Wyoming, United States of America. These species belong to the family Cervidae. Cases have occurred primarily in captive animals but a few affected free-ranging animals have been identified. Clinical disease in both species is characterised by progressive weight loss, behavioural alterations and excessive salivation. In deer polydipsia and polyuria also commonly occur. Significant lesions are confined to the central nervous system and consist of spongiform change in grey matter, intraneuronal vacuolation, astrocytosis and amyloid plaques. Inflammatory reaction is absent.The origin of this disease is not known. In contrast to the cases of spongiform encephalopathy recognised in five species of antelope (family Bovidae) in British zoological parks, which are an extension of the current bovine spongiform encephalopathy epizootic, CWD is not the result of food-borne exposure to the infectious agent. CWD appears to be maintained within captive populations by lateral and, possibly, maternal transmission.Spongiform encephalopathies in wild ruminants are currently geographically isolated and involve relatively small numbers of animals. However, these potentially transmissible diseases could be of greater importance in the future and should be viewed with concern in the light of international movements of wild ruminants and the current expansion of the game farming and ranching industry in many parts of the world.

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Abstract. Th e path ology of the centra l ner vou s system of nine mul e deer (Odocoileus hemionus) and six elk (Cervus elaphus nelsoni) with chro nic wasting d isease, a spongiform encepha lopathy o f mul e deer and elk, was stud ied by light microscop y. Lesion s were sim ilar in both species and were characterized by spo ngiform transformati on of gray matter , intracytopl asm ic vacuolati on of neuron s, neuronal degenerati on and loss, astro cytic hypertroph y and hyperpl asia , occur rence of am yloid plaques, and absence of significant inflammatory respon se. Distributi on and severity of lesion s were eva luated at 57 locati on s; there were only min or differences between deer and elk. Co nsis tent, severe lesion s occ urred in olfacto ry tub ercle and cortex, hypoth alamus, and the parasym path etic vaga l nucleus of deer, and sectio ns examined from these region s would be sufficient to esta blish a di agnosis ofchron ic wasting di sease. Lesions were mi lder in these locat ions in elk but were sufficiently appare nt to be of diag nos tic va lue. Other differe nces included increased severi ty of lesion s some th alamic nuclei in elk in contrast to deer, the occurrence of amy loid plaqu es dem on str able by hem at oxylin and eosi n and histoche mica l sta ins in deer in contrast to elk, and th e presence of mild white matter lesion s in elk but not in deer. Lesion s of chro nic wasting di sease were qu alit ati vely compa rab le to those of scrapie, bovin e spo ngiform encepha lopa thy, tran smi ssible m ink ence phalopathy, and the human spongiform encephalopa thies. To pographic di str ibution and lesion seve rity of chro nic wasting di sease were most similar to those of scrapie and bo vin e spo ngiform enceph alop ath y. Durati on o f clini cal di sease did not signifi cantly influence lesion di stribution or severi ty in eithe r spec ies.Key words: Central ner vou s system; Cervus elaphus nelsoni ;elk; mul e deer ; Odocoileus hem ionus;spo ngiform ence pha lopa thy.Chronic wasting disease (CWD), a spontaneous neurolo gic disease of captive mul e deer (Odocoileus hemionus) and Rocky Mountain elk (Cervus elaphus nelsoni), has been recogniz ed since 1967 and 1979 , respectively, in wildlife facilities in Colorado and Wyoming.21.22 Th e disease is characterized by emaciation, changes in beha vior , and excessive salivation in both species and in deer, addi tio nally by polydip sia and polyuria. Clinical course is from severa l weeks to 8 months and the disease is invariably fatal. At necropsy, affected anima ls are emaci ated but other gross lesions have not been found consistently. Ruminal contents of deer are excessive ly fluid, reflecting polydip sia in this species. Various oth er gross changes, parti cularl y aspiration pneumonia, are inconsistentl y present and hav e been considered the result of int ercurrent or seconda ry disease pro cesses. Consistent microscopi c alteration s have been found only in the central nervous system (CNS) and ha ve been characterized as a spongiform encephalopath...