Detection of Betanodavirus in experimentally infected European seabass (Dicentrarchus labrax, Linnaeus 1758) using non‐lethal sampling methods

One of the major disease threats affecting the Mediterranean aquaculture industry is viral encephalopathy and retinopathy (VER). The target organs for Betanodavirus detection are the brain and eyes, obtained through lethal sampling. This study aimed to evaluate the efficacy and suitability of non-lethal samples for detecting Betanodavirus in European seabass (Dicentrarchus labrax). European seabass juveniles were infected with Betanodavirus, by either an intramuscular injection or immersion (10⁷ TCID₅₀ /ml and 10⁶ TCID₅₀ /ml, respectively), and samples collected 7, 15 and 30 days post-infection (dpi). The brain was collected as a lethal sample, and gills, caudal fin and blood as non-lethal tissues for detecting Betanodavirus by quantitative reverse transcription PCR (RT-qPCR). The presence of virus in non-lethal tissues was inconsistent, with lower viral loads than in the brain. For blood, higher viral loads were detected in intramuscular-infected fish at 15 dpi until the end of the challenge. Serum antibodies against Betanodavirus were assessed using an enzyme-linked immunosorbent assay (ELISA). Antibodies were detected as early as 7 dpi, with higher mean antibody titres at 15 and 30 dpi. The presence of Betanodavirus-specific antibodies indicates that this is a suitable evaluation method for detecting early stages of the infection.