Keynote-2
MOLECULAR EPIDEMIOLOGY OF BETANODAVIRUSES IN EUROPE
R. Thiéry*
Afssa Sophia-Antipolis, BP 111, 105 route des chappes F-06902, Sophia-Antipoli, France
*r.thiery@afssa.fr
In recent years, betanodaviruses have been detected in an increasing number of cultured and
wild fish species in Europe. In most circumstances, but not always, Viral Nervous Necrosis (or
Viral Encephalopathy and Retinopathy) was associated to the presence of these viruses.
Molecular epidemiological tools have been developed by our group and by others with the aim
to help to the identification of the origin of the infections and mostly relied on the sequencing of
the capsid protein gene and subsequent phylogenetic reconstruction. According to this, most
European isolates were assigned to one of the genotype described by Nishizawa et al, (1997)
(SJNNV, TPNNV, BFNNV and RGNNV).
However recent data indicate that molecular epidemiology of betanodaviruses in Europe
could be more complex than thought previously. First, a betanodavirus isolates from turbot in
Norway could not be assigned to any existing genotype suggesting that it belongs to a fifth
genotype (Johansen et al, 2004). Second, sequencing of the capsid protein gene of a
betanodavirus isolate obtained from Senegalese Sole in Spain indicated a high homology with
the capsid protein gene the Striped Jack Nervous Necrosis Virus previously only known in
Japan (Thiéry et al, 2004). This observation was further confirmed in the European sea bass and
sea bream cultured in the Iberian peninsula. Third, the BFNNV type, was observed in one
occasion in the European sea bass cultured in France, whereas it was previously known to
mainly affect cold water species. In addition, phylogenetic analysis of the RNA1 fragment
encoding the RNA-dependant RNA polymerase (RdRp) suggested that the RdRp of French
isolates clustered in three major groups but that the phylogenetic position of some isolates did
not agree with the trees based upon analysis of the capsid protein gene. This suggested that
reassortement between the RNA1 and RNA2 fragments could occurred between some strains
(Névarez et al, 2004).
Altogether, this new knowledge underlined the importance of a more thorough
characterisation of the betanodavirus isolates by sequencing both genomic fragments for typing
purpose and suggest that the taxomomy of betanodaviruses should be revised.
References:
Nishizawa T., M. Furuhashi, T. Nagai, T. Nakai, and K. Muroga (1997). Genomic classification
of fish nodaviruses by molecular phylogenetic analysis of the coat protein gene Appl.
Environ. Microbiol. 63, 1633-1636.
Johansen R., I. Sommerset, B. Torud, K. Korsnes, M. J. Hjortaas, F. Nilsen, A. H. Nerland, and
B. H. Dannevig. (2004). Characterization of nodavirus and viral encephalopathy and
retinopathy in farmed turbot, Scophthalmus maximus (L.). J. Fish. Dis. 27, 591-601.
Thiéry R., J. Cozien, C. de Boisséson, S. Kerbart - Boscher, and L. Névarez. (2004) Genomic
classification of new betanodavirus isolates by phylogenetic analysis of the coat protein
gene suggests a low host fish species specificity. J. Gen. Virol. 85, 3079-3087.
Névarez L., J. Cozien, and R. Thiéry. (2004) Characterization of the RNA-dependent RNA
polymerase gene of isolates of Viral Encephalopathy and Retinopathy Virus. 6th
International Symposium on Viruses of Lower vertebrates, Hakodate, Japan, P-15.