Development and application of antibody microarray for lymphocystis disease virus detection in fish

Generation, characterization and application of monoclonal antibodies against matrix protein of hirame novirhabdovirus (HIRRV) in flounder

Hirame novirhabdovirus (HIRRV) causes severe disease in fish cultures, resulting in great economic loss in Asia and Europe. In this study, the matrix protein (M) of HIRRV was recombinantly expressed as the immunogen to produce monoclonal antibodies (MAbs) using hybridoma cell fusion technology, and 3 MAbs were produced and characterized by indirect ELISA, Western blotting and immunofluorescence assay (IFA). Western blotting and mass spectrometric analysis showed that the MAbs could specifically react with the nature M protein of HIRRV. The MAbs were employed to detect virions in HIRRV-infected epithelioma papulosum cyprini (EPC) cells and flounder Paralichthys olivaceus by IFA and immunohistochemistry (IHC). In the virus-infected EPC cells, the virions were mainly located in the cytoplasm, whereas in flounder, HIRRV was present in all 10 tested tissues, and the positive signals in spleen, head-kidney and heart were higher than in other tissues, consistent with the results obtained by RT-PCR. Moreover, strong positive signals were observed in the endothelial cells of blood vessels, but only the leukocytes were infected by HIRRV in the whole blood cells. These results indicate that the high susceptibility to HIRRV of leukocytes and endothelial cells may facilitate the spread of HIRRV and finally cause systemic infection in flounder. This study provides a foundation for further studies on rapid diagnosis of HIRRV and its infection mechanisms.

Rapid and Sensitive Detection of Lymphocystis Disease Virus Genotype VII by Loop-Mediated Isothermal Amplification

Lymphocystis disease virus (LCDV) infections have been described in gilthead seabream (Sparus aurata L.) and Senegalese sole (Solea senegalensis, Kaup), two of the most important marine fish species in the Mediterranean aquaculture. In this study, a rapid, specific, and sensitive detection method for LCDV genotype VII based on loop-mediated isothermal amplification (LAMP) was developed. The LAMP assay, performed using an apparatus with real-time amplification monitoring, was able to specifically detect LCDV genotype VII from clinically positive samples in less than 12 min. In addition, the assay allowed the detection of LCDV in all asymptomatic carrier fish analysed, identified by qPCR, showing an analytical sensitivity of ten copies of viral DNA per reaction. The LCDV LAMP assay has proven to be a promising diagnostic method that can be used easily in fish farms to detect the presence and spread of this iridovirus.