Echigo-1: a panencephalopathic strain of Creutzfeldt-Jakob disease. II. Ultrastructural studies in hamsters.

In this and a companion paper we present immunohistochemical and ultrastructural data on hamsters infected with the Echigo-1 strain of Creutzfeldt-Jakob disease. Ultrastructurally, two types of vacuoles were readily discriminated in the brain: the grey matter vacuoles of spongiform change and intramyelin vacuoles. The vacuoles were always membrane-bound; the membranes were single or double. The axons were entirely missing from the plane of the sections or, if visible, were shrunken and attached to the innermost layer of the myelin. It was noteworthy that some vacuoles indented cell bodies or processes and thus were reminiscent of the intraneuronal vacuoles typical for natural scrapie, BSE and CWD in ungulates and cervids but not of the vacuoles encountered in rodent models of scrapie and CJD. We also noticed vacuoles distending myelinated fibres in which the axons had become dystrophic. Some axons underwent Wallerian degeneration while others met the criteria for dystrophic neuritis. Both alterations existed in the same areas. Typical dystrophic neurites contained abnormal subcellular organelles, mainly electron-dense lysosomal inclusions. Other neurites contained numerous multi-vesicular bodies and autophagic vacuoles. Nuclear paracrystalline rod-like inclusions were occasionally visible in neurons while other inclusions comprised spiroplasma-like inclusions in synaptic boutons. The robust cellular reactions consisted of reactive astrocytes and macrophages filled with cellular debris. It is of note that complex autophagic vacuoles were observed in the cytoplasm of neurons.