Echigo-1: a panencephalopathic strain of Creutzfeldt-Jakob disease: ultrastructural studies of the optic nerve.

The Echigo-1 strain of CJD was isolated by Mori and colleagues (1989) from a case of 33-year-old female with a panencephalopathic type of CJD. An incubation period following intracerebral inoculation of hamsters with 10% cleared suspension of the Echigo-1-affected brain was approximately six months. We report here ultrastructural changes which are comparable with those in the white matter of another panencephalopathic type of CJD, the Fujisaki strain of CJD (GSS) passaged in mice. Vacuoles developed within myelinated axons: within axoplasm or within the myelin sheath and these were accompanied by exuberant reaction of macrophages and hypertrophic astrocytes. Axons underwent Wallerian degeneration and dystrophic neurites were also seen. Most important, we observed proliferation of inner mesaxons. Cross-sectional profiles of innumerable myelinated fibers contained membranous organelles which were continuous with the inner lamellae of the oligodendroglial cells. These unusual proliferations of inner mesaxon formed whorls and elaborated loops. In some axons, proliferation was so severe that loops of mesaxon filled the whole cross-section of the axon. Occasionally, we observed intrusion of the membranous tongue of the inner mesaxon into axoplasm. This study presents a second panencephalopathic model of CJD available in small laboratory rodents. It is important because this is the only such model in hamsters and it may be used for comparative studies of different strains of agent in the same host; thus far only mouse and hamster model have been available for comparative studies.