Detection of lymphocystis disease virus (LCDV) from yellowbar angelfish (Pomacanthus maculosus Forsskål, 1775) in Iran: Histopathological and phylogenetic analysis

Lymphocystis disease (LCD) is a benign viral disease characterized by the appearance of hypertrophic fibroblastic cells in the connective tissues of fish. In December 2021, a group of yellowbar angelfish (Pomacanthus maculosus Forsskål, 1775) which had significant mortalities (10%) and showed whitish nodules on the fins and skin, were packed in water-filled plastic bags, supplied with oxygen, and transported to the Ornamental Fish Clinic, Faculty of Veterinary Medicine, University of Tehran (Tehran, Iran). Following the clinical inspection and observation of whitish clusters of nodules mostly on the fins and skin by stereomicroscopy, wet smears of skin and fins revealed numerous hypertrophic lymphocystis cells. Histopathological study of the whitish nodules in skin and fins revealed many hypertrophic cells with thick hyaline capsules, irregular nucleus, and multiple intracytoplasmic inclusion bodies. In addition to the extension of hypertrophic lymphocystis cells' growth until the superficial muscle layer, infiltration of inflammatory cells and hemorrhage between hypertrophic cells are also observed. The hyaline capsule of hypertrophic fibroblasts stained with the PAS. Molecular characterization (PCR) confirmed the presence of Lymphocystis disease virus (LCDV) in the external nodules and the internal organs homogenate of the infected fish. Sequence analysis of the MCP gene of the detected virus (IR_LCDV_RGZIS) assigned it to genogroup 5. This is the first detection and characterization of LCDV in yellowbar angelfish (Pomacanthus maculosus) in Iran.