Experimental vertical
transmission of nodavirus from broodfish to eggs and larvae of the sea bass,
Dicentrarchus labrax (L.)
G. Breuil, J.F.P. Pépin, S. Boscher, R. Thiéry-2002
Journal of Fish Diseases, 25(12): 697-714
Abstract:
Adult broodstock sea bass, Dicentrarchus labrax
(L.), were intramuscularly inoculated with live Sb-Atl nodavirus strain and
maintained at two different water temperatures (13 and 20 °C) until
spawning. Each spawn was then incubated separately in UV treated water for 3 days
and newly hatched larvae reared for 22 days at 13-15 °C. The
inoculated broodfish developed a specific immune response following
inoculation with the live virus and specific antibodies were detected in the
sera of all the inoculated fish whatever the temperature used (13 and 20 °C).
Specific nodavirus antigen was also detected by enzyme-linked immunosorbent
assay (ELISA) and nested reverse transcription-polymerase chain reaction
(RT-PCR) in the brain and the liver of these fish. Vertical transmission of
the nodavirus disease was demonstrated following inoculation of the
broodfish with the live virus strain, as typical lesions associated with the
nodavirus antigen were detected by immunohistochemistry in the brain of
larvae at days 14-22 following hatching. The eggs from seven inoculated
females that spawned during the experiment were tested for nodavirus by
antigen ELISA, RT-PCR and nested RT-PCR. Fertilized and non-fertilized eggs,
as well as developing larvae, were found nodavirus positive using these
techniques. However, the nested RT-PCR was the only technique that could
detect the nodavirus in ovarian biopsies before spawning. Therefore, the
selection of nodavirus-free sea bass broodstock cannot be achieved by ELISA
or RT-PCR testing of ovarian biopsies. Alternative methods such as serum
nodavirus antibody detection of broodstock and/or nested RT-PCR testing of
eggs before spawning should be used.
(Laboratoire
de Recherche Aquacole, IFREMER, Chemin de Maguelone, 34250
Palavas-les-Flots, France. e-mail: gilles.breuil@ifremer.fr)