Isolation and molecular characterization of viral encephalopathy and retinopathy virus from gilthead seabream larvae (Sparus aurata) showing mass mortalities

Gilthead seabream (Sparus aurata, L.1578) has been reared since several years in close connection with the European seabass (Dicentrarchus labrax) often affected by severe losses caused by viral encepahalopathy and retinopathy (VER) without showing any clinical sign or mortality. This observation led to consider Sparus aurata a species completely resistant to betanodavirus infection. In 2001, Castric et al., during a VER outbreak affecting a farmed seabass population, succeeded to obtain a VER isolate from asymptomatic seabream, collected in the same farm. In the following years several rumours about seabream larvae mortalities caused by betanodavirus infections have circulated among farmers and in the scientific world but very few investigations have been performed. In 2007, Beraldo et al. described the occurrence of a betanodavirus outbreak in sea bream larvae showing mass mortalities. Clinical signs, histological and immunohistochemistry findings were described. Frozen samples belonging to the same outbreak were accidentally made available later on by the farmer and processed for virus isolation and characterization. In the present study we describe the isolation of the causative agent in SSN-1 cells, its identification by PCR and molecular characterization as reassortant virus containing the genome from RGNNV (RNA1) and SJNNV(RNA2) genotypes. Our findings corroborate the preliminary results described by Beraldo et al. and definitively demonstrate that gilthead seabream must be included in the list of VER susceptible species at least during larval stage. References Beraldo P., G. De Nigris, F. Rogato and M. Galeotti (2007). Histological and immunohistochemistry findings of viral encephalopathy-retinopathy in gilthead seabream larvae (Sparus aurata, L. 1578) reared in Italy. Book of abstract 13th international conference of the EAFP, diseases of fish and shellfish . Grado, 17-22 September 2007.