Ultrastructural features of herpesvirus-infected cells in epidermal lesions in larvae of the Japanese flounder Paralichthys olivaceus.

An electron microscopic study (EM) was performed on herpesvirus-infected cells in epidermal lesions of larvae of the Japanese flounder Paralichthys olivaceus to document the ultrastructure of the lesions. Epithelial cells were the primary cell type infected with the herpesvirus, and showed nuclei containing nucleocapsids, vesicles containing enveloped virions in the cytoplasm, and the release of enveloped virions through the cell membrane. Herpesvirus-infected cells were highly vacuolated and necrotic showing fragmented nuclei while these cells retained firm desmosomes to prevent separation from neighboring necrotic cells, which caused cellular aggregation in the upper layer of the epidermis. Based on EM results, the definitive pathological change was necrosis of epithelial cells infected with the flounder herpesvirus; therefore, the name Viral Epidermal Necrosis (VEdN) is appropriate for this herpesvirus infection.