Ultrastructural neuropathology of chronic wasting disease in captive mule deer.

Chronic wasting disease (CWD), a progressive and uniformly fatal neurological disorder, is characterized neuropathologically by intraneuronal vacuolation, spongiform change of the neuropil and astrocytic hyperplasia and hypertrophy. Ultrastructural neuropathological findings consist of (1) extensive vacuolation in neuronal processes, within myelin sheaths, formed by splitting at the major dense lines or within axons; (2) dystrophic neurites (dendrites, axonal preterminals and myelinated axons containing degenerating mitochondria and pleomorphic, electron-dense inclusion bodies); (3) prominent astrocytic gliosis; (4) amyloid plaques; and (5) giant neuronal autophagic vacuoles. Other findings include activated macrophages and occasional spheroidal structures containing densely packed fibrillar material of unknown origin, abundant structures suggestive of degenerating microtubules entrapped in filamentous masses, vacuoles and myelin figures. Similar findings have been previously observed in scrapie-infected hamsters and Creutzfeldt-Jakob disease (CJD)-infected mice, bovine spongiform encephalopathy, and CJD indicating that CWD in captive mule deer belongs to the subacute spongiform encephalopathies (transmissible brain amyloidoses).