In this study, the susceptibility of 5-g juvenile European sea bass
was evaluated by intramuscular injection (105 TCID50/g) using isolates belonging
to the RGNNV and SJNNV genotypes as well as a reassortant isolate (RGNNV
RNA1/SJNNV RNA2) obtained from Senegalese sole (Solea senegalensis).
In these experimental infections, the cumulative mortality was determined.
Furthermore, quantification of viral genome, by absolute real time PCR, and
infective viral particles, by virus titration, was performed from brains of dead and
survivor fish (30 days post-inoculation). In addition, anti-VNNV antibodies in
sera from survivor animals were determined by indirect ELISA. Typical
symptoms of VNN and mortality were only recorded in fish inoculated with the
RGNNV (47% cumulative mortality) and the reassortant (33%) isolates.
However, high levels of viral genome and infective viral particles were recorded
in brain of survivor fish inoculated with the SJNNV isolate, although did not
cause mortality or clinical signs. Specific antibody response, measured by indirect
ELISA, was only observed in the VNNV-inoculated groups, with titres of 1/1024,
1/4096 and 1/8192 for RGNNV, SJNNV and reassortant inoculated animals,
respectively.
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