Viral nervous necrosis (VNN) is a disease that affects farmed fish worldwide. Its etiologic agent is the nervous necrosis virus (NNV), genus Betanodavirus, family Nodaviridae. NNV are small and non-enveloped viruses with a genome consisting of two molecules of positive-sense single-stranded RNA, RNA1 and RNA2, which encode the RNA-dependent RNA polymerase and the capsid protein, respectively. The betanodaviruses have been classified into four species: Striped jack nervous necrosis virus (SJNNV), Tiger puffer nervous necrosis virus (TPNNV), Red-spotted grouper nervous necrosis virus (RGNNV), and Barfin flounder nervous necrosis virus (BFNNV). In Southern Europe, natural reassortants between RGNNV and SJNNV have been isolated from Senegalese sole (Solea senegalensis), gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) associated to VNN outbreaks. Immune response against betanodavirus infections has been poorly studied in gilthead seabream. In this study, fish were challenged by intramuscular (im) injection or by immersion, using a reassortant strain containing RGNNV-type RNA1 and SJNNV-type RNA2 segments. Head kidney and brain samples were collected at 24, 48 and 72 h post-challenge (pc) for the injection experiment, while in the bath challenge sampling was performed at 48 and 72 h pc. The immunogen expression analysis was carried out using the platform OpenArray®. In the im-injected fish, 21 differentially expressed genes (DEGs) were identified in head kidney samples at 24 h pc, whereas a lower immune response was detected at 48 and 72 h pc (11 and 9 DEGs, respectively). In brain samples, a delayed response was observed, with 32 DEGs recorded at 72 h pc. Regarding the bath-challenged fish, fewer immunogenes were differentially expressed although all of them were up-regulated. This research was funded by the Ministerio de Ciencia, Innovación y Universidades (MCIUI) and FEDER under Grant RTI2018-094687-B.
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