Neuropathology of Chronic Wasting Disease of Mule Deer (Odocoileus hemionus) and Elk (Cervus elaphus nelsoni)

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Abstract
The pathology of the central nervous system of nine mule deer (Odocoileus hemionus) and six elk (Cervus elaphus nelsoni) with chronic wasting disease, a spongiform encephalopathy of mule deer and elk, was studied by light microscopy. Lesions were similar in both species and were characterized by spongiform transformation of gray matter, intracytoplasmic vacuolation of neurons, neuronal degeneration and loss, astrocytic hypertrophy and hyperplasia, occurrence of amyloid plaques, and absence of significant inflammatory response. Distribution and severity of lesions were evaluated at 57 locations; there were only minor differences between deer and elk. Consistent, severe lesions occurred in olfactory tubercle and cortex, hypothalamus, and the parasympathetic vagal nucleus of deer, and sections examined from these regions would be sufficient to establish a diagnosis of chronic wasting disease. Lesions were milder in these locations in elk but were sufficiently apparent to be of diagnostic value. Other differences included increased severity of lesions in some thalamic nuclei in elk in contrast to deer, the occurrence of amyloid plaques demonstrable by hematoxylin and eosin and histochemical stains in deer in contrast to elk, and the presence of mild white matter lesions in elk but not in deer. Lesions of chronic wasting disease were qualitatively comparable to those of scrapie, bovine spongiform encephalopathy, transmissible mink encephalopathy, and the human spongiform encephalopathies. Topographic distribution and lesion severity of chronic wasting disease were most similar to those of scrapie and bovine spongiform encephalopathy. Duration of clinical disease did not significantly influence lesion distribution or severity in either species.