Diagnosis of lymphocystis disease in a novel host, the whitemouth croaker Micropogonias furnieri, associated with a putatively novel Lymphocystivirus species (LCDV-WC).

Abstract

In 2015, an episode of lymphocystis disease (LCD) was detected in wild and cultured populations of whitemouth croaker Micropogonias furnieri off the coast of Uruguay. Fish of both origins were collected for histopathological and molecular investigations. Macroscopically, multinodular tumorlike masses were observed in the skin. Histological examination of these masses revealed enlarged cells with a hyaline capsule and basophilic inclusion bodies in the cytoplasm. The inclusion bodies were further examined by electron microscopy and showed icosahedral virions with a median diameter of 182 nm. Routine molecular investigations targeting the DNA polymerase and major capsid protein genes showed the presence of the DNA of an unknown lymphocystis disease virus (LCDV) in all specimens showing external signs of LCD. Subsequently, 4 other core genes were amplified and sequenced from the viral genome. Phylogenetic tree reconstruction based on the concatenated sequence of 6 core genes indicated that the virus undoubtedly belongs to the genus Lymphocystivirus. However, the core gene sequences of the whitemouth croaker LCDV differ markedly from those of the 3 known LCDVs, putatively representing a fourth LCDV species.