Experimental transmission of encephalopathy and retinopathy induced by nodavirus to sea bream, Sparus aurata L., using different infection models

The transmission of viral encephalopathy and retinopathy (VER) was investigated in juvenile sea bream, Sparus aurata L. Two different infection routes [intraperitoneal (i.p.) and intramuscular injection (i.m.)] were tested at two different temperatures (20 and 26 degreesC) using sea bream of mean weight 0.7, 2 and 4 g, as well as an immersion challenge performed at 26 degreesC with sea bream of 0.7 g. Successful transmission of the disease was only achieved by i.m. injection. Mortalities of 100% occurred in sea bream of 0.7 g at day 15 post-infection and 47% in sea bream of both 2 and 4 g at day 30 post-infection in all the experimental infections at 26 degreesC. No mortalities were ever observed with infections at 20 degreesC. When mortalities were observed, the virus was detected by immunoperoxidase staining in the SSN-1 cell line inoculated with tissues from infected fish. Histological examination of both normal and infected fish showed a vacuolization in the bipolar and granular layers of the retina of the infected sea bream. This is the first experimentally induced transmission of VER in sea bream. Differences were observed at the time of disease onset depending on water temperature, the route of infection and the age of the juvenile fish.