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.
Highlights
Lymphocystis disease (LCD) is the viral infection most frequently reported in gilthead seabream (Sparus aurata) farms in the South Atlantic and Mediterranean areas [1]
These nodules consist of Lymphocystis disease virus (LCDV)-infected hypertrophied dermal fibroblasts, named lymphocysts or lymphocystis cells [11, 21, 22]
LCDV is considered a dermatropic virus [8]; in some fish species, lymphocysts have been observed in the mesenteries, peritoneum, and several internal organs, which could indicate that the infection can become systemic under certain conditions [4, 7, 23, 24]
Summary
Lymphocystis disease (LCD) is the viral infection most frequently reported in gilthead seabream (Sparus aurata) farms in the South Atlantic and Mediterranean areas [1]. LCD is a self-limiting disease characterized by the hypertrophy of fibroblastic cells in the connective tissue of fish [3] These hypertrophied cells, named lymphocysts or lymphocystis cells, are usually observed on the skin and fins, they have been described in several internal organs (such as the stomach, spleen, liver, kidney and heart) [4,5,6,7,8]. Several studies have shown that viral antigens can be detected in a number of organs of infected fish, in lymphocystis lesions [13,14,15]. Viral genomes and antigens were detected in the different organs analysed, including the caudal fin, gills, intestine, liver, spleen and kidney, suggesting that LCDV establishes a systemic and persistent infection in this fish species. Further studies are necessary to confirm these results and to establish if these infections are productive
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