Two isolates of sea bass, Dicentrarchus labrax L., nervous necrosis virus with distinct genomes

Diagnosis by reverse-transcriptase polymerase chain reaction (RT-PCR) ampli fication using previously published primers specific for the capsid protein gene of fish nodaviruses detected an isolate of sea bass, Dicentrarchus la brax L., nervous necrosis (SBNNV) from the French Mediterranean coast, but did not detect an isolate from the Atlantic coast. The capsid protein codin g sequence of the nodavirus of both isolates was cloned. Sequence analysis revealed that the Mediterranean isolate was identical to the sequence previ ously published for SBNNV, while the Atlantic isolate is related, but carri ed numerous substitutions, in particular in the region used for RT-PCR diag nosis. A new primer set was tested which detected the viral genome of the A tlantic isolate. Using the new primer set, PCR amplification of a range of 10-fold dilutions of a plasmid containing the capsid protein gene of the At lantic isolate showed that the limit of detection of the assay was between 10 and 100 copies of plasmid.