Morphogenesis of largemouth bass ranavirus (LMBRaV) in the epithelioma papulosum cyprinid cell line

Largemouth bass ranavirus (LMBRaV) belongs to the Ranavirus genus of the Iridoviridae family. It is a highly pathogenic virus that causes mass mortality in largemouth bass. In recent years, outbreaks of LMBRaV have been found in various provinces throughout China. Previous research mainly focused on virus isolation, identification, and detection, while the morphological change of the virus was still unknown. In this study, the ultrastructural morphogenesis of LMBRaV in epithelioma papulosum cyprinid (EPC) cells was observed and studied by using transmission electron microscopy. EPC cells were infected with LMBRaV (MOI=0.1) and then examined at 2 h, 4 h, 6 h, 12 h, 24 h, 48 h, 72 h and 96 h post infection. LMBRaV entered cells through endocytosis or direct penetration of cell membrane. After entering, the virus was observed in vesicles or lysosomes. After capsid uncoating, the virus genomes passed through the nuclear membrane and entered the cell nucleus. Virus genomes completed replication in the nucleus then transferred into the cytoplasm. In the cytoplasm, the progeny virus was assembled in the viromatrix and then aggregated in pseudocrystalline array. Finally, mature virus particles released through budding release from the cell membrane. Mature virus particles had a hexagonal shape and a diameter of approximately 150 nm. This study revealed the process of morphogenesis of LMBRaV in EPC cell line, providing essential information for further research on pathogenic mechanisms and immunological prevention of LMBRaV.