New Tools for the Detection of Sea bass Nodavirus - 2) Viral sources and virulence for eggs and the larvae

Aquaflow Technical Leaflet 2002-72

European Network for the Dissemination of Aquaculture RTD Information (Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/

Nodaviruses are responsible for a viral disease characterised by the degeneration of the brain and retina in several species of fish, including the sea bass. The aim of this work was to study the transmission and virulence of two genetically distinct viral strains of different origins on the eggs and larvae of sea bass, using an immunological test (ELISA: Enzyme-Linked Immunosorbent Assay) performed on homogenised larval tissue. The viral strains were isolated from sick sea bass taken from farms on the Atlantic coast (Atlantic strain SB1) or on the Mediterranean coast (Mediterranean strain SB2).

The Atlantic strain performed particularly well in the immunological test. The Atlantic viral strain SB1 is more pathogenic for eggs than SB2 when an experimental contamination was carried out at the time of fertilisation. Strains SB1 and SB2 are also pathogenic for larvae, and the cerebral lesions that are characteristic of the disease appeared between 4 and 6 days after challenge. This immunological test can be used to detect the virus in larvae before the clinical and behavioural signs of the disease appear.

In conclusion, the development of a test to screen for nodavirus in the tissues of sea bass at an early developmental stage of the egg and the larvae complements the panoply of tests recommended by the International Office of Epizootic Diseases (IOED) for the detection of viral pathologies in fish. This immunological test on tissues complements the one previously developed for the detection of anti-nodavirus antibodies in the blood of adult sea bass and opens up the prospect of early detection and control of contaminated fish in fish farms. Moreover, it provides new data concerning the virulence of two genetically different strains of nodavirus during the larval development of the fish.

For more information:

BREUIL Gilles
IFREMERLaboratoire Recherche Piscicole de Méditerranée
Chemin de Maguelone
France
Phone : +33 467504004
Fax : +33 467682885

e-mail : gbreuil@ifremer.fr

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