Feed and immersion challenges with lymphocystis disease virus (LCDV) reveals specific mechanisms for horizontal transmission and immune response in senegalese sole post-larvae

The horizontal transmission of lymphocystis disease virus (LCDV) through contaminated water and feed (using artemia as vehicle) and the associated immune gene expression profiles in Senegalese sole post-larvae were investigated. All specimens analyzed were positive for LCDV DNA detection at 1-day post-challenge (1 dpc) with the highest viral levels in specimens infected through the immersion route. However, the percentage of LCDV-positive animals and number of viral DNA copies dropped progressively at 2 and 7 dpc. The histological analysis identified structural changes in the skin, muscle and gills of sole post-larvae LCDV-challenged by immersion. In situ hybridization confirmed a wide distribution of LCDV in the skin, gut, surrounding vessels in trunk muscle and head kidney in the immersion route, while the signals were restricted to the liver and lamina propria in the feeding treatment. Expression analysis using a set of 22 genes related to innate immune defense system demonstrated clear differences in the time-course response to LCDV as function of the infection route. Most antiviral defense genes, the proinflammatory cytokines, the complement c3, g-type lysozyme and T-cell markers cd4 and cd8a were rapidly induced in the feeding-infected post-larvae, and they were remained activated at 2 dpc. In contrast, in the immersion-infected post-larvae the induction of most defensive genes was delayed, with a low intensity at 2 dpc. All these data demonstrate that LCDV can horizontally infect Senegalese sole post-larvae through the water or feed although with different patterns of histopathological disorders, virus distribution and route-specific expression profiles.This study has been funded by MCIU/AEI/FEDER, UE Project RTA2017-00054-C03-01 and cofunded 80% by Programa Operativo FEDER de Andalucía 2014–2020, project PP.AVA.AVA201601.9 “Nuevas herramientas genómicas para el análisis genético y evaluación transcriptómica de compuestos funcionales basados en microalgas para impulsar la acuicultura del lenguado (SOLEALGAE)”. In addition, it was also partially supported by Proyecto de Excelencia, Junta de Andalucía, P12-RNM-2261. Carlos Carballo was supported by an INIA PhD grant (2014)