Lymphocystis Disease Virus in Largemouth Bass - A Case Report

Lymphocystis disease caused by the lymphocystis disease virus (LCDV) infects numerous fish species including wild and farmed fish from several families. The LCDV is a DNA virus belonging to the family Iridoviridae. The virus usually causes benign, chronic infection characterized by macroscopic nodules located on the body, fins, and gills of fish, although other tissues may be infected occasionally. The disease normally does not cause significant mortalities, but massive infections leading to substantial mortalities have been reported in some aquacultured species such as sea bream (Sparus aurata), Olive flounder (Paralichthys olivaceus), Japanese seabass (Lateolabrax japonicus), and rockfish (Sebastes schlegeli). In this study, nodules from the fins of a largemouth bass (Micropterus salmoides) were subjected to pathological examination. Microscopic analysis of the wet mount and the histological analysis revealed the pathological alterations caused by the lymphocystis disease virus. Histopathological analysis indicated that the nodules contained encapsulated hypertrophic cells typical of the viral infection. The inoculum from the fin nodules produced cytopathic effects (CPEs) on Bluegill Fry (BF-2) cells, while no CPEs were observed in the Epithelioma Papulosum Cyprini (EPC) and Fathead Minnow (FHM) cell lines. These findings suggest that the causative agent of the fin infection in the largemouth bass is lymphocystis disease virus.