Abstract: The pathogen Hyriopsis cumingii Plague Virus isolated from the diseased H. cumingii Lea has been artificiallytransferred to the healthy H. cumingii Lea. The infected H. cumingii Lea has displayed some typical pathologicalchanges. Observations by histopathology have showed that most of organs including the digestive gland, stomach andintestine are the primary targets of the plague virus. Lesions have been observed, accompanied with a number of emptyareas, cell vacuolization and some cells falling-off. Arenavirus-like particles have been detected by using transmissionelectron microscopic (TEM) examination on investigated organs of the artificially infected bivalve mussel Hyriopsiscumingii. Virions are spherical with a size of 120 nm in diameter, and the outer layer of the intact arenavirus-like particleshave small protuberance and moderate electron-dense nucleicapsid. Under electronic microscope, the most obviouscellular pathologic feature is the large vacuole areas of cytoplasm, and there is the reduction or devoid of organelles inthe cytoplasm. Varying degrees of denaturalization and necrosis have been found in the intestinal mucosa epithelial cells.We have also observed that in cytopathic cells of digestive gland, the nuclei has been discovered to be amorphous andhypertrophied. There are denaturalizationand necrosis in the epithelial cell of gill and the nucleus membrane of granulocyteshave been dissolved.