Abstract
The lymphocystis disease (LCD), the main viral pathology described in cultured gilthead seabream (Sparus aurata), is a self-limiting condition characterized by the appearance of hypertrophied fibroblasts (named lymphocysts) in the connective tissue of fish, primarily in the skin and fins. The causative agent of the disease is the Lymphocystis disease virus (LCDV), a member of the Iridoviridae family. In the present study, LCDV genome and transcripts were detected by real-time PCR in caudal fin, as well as in several internal organs, such as intestine, liver, spleen, kidney and brain, from asymptomatic, diseased and recovered gilthead seabream juveniles. These results indicate that the LCDV has a broad range tissue tropism, and can establish a systemic infection, even in subclinically infected fish. As showed by in situ hybridization, the permissive cells for LCDV infection seem to be fibroblasts, hepatocytes and cells of the mononuclear phagocyte system. Histopathological alterations associated with LCD were observed in all the organs analysed, including necrotic changes in liver and kidney, inflammatory response in the intestine submucosa or brain haemorrhage, although lymphocysts were only detected in the dermis of the caudal fin. Nevertheless, these histological changes were reverted in recovered animals.