Viral encephalopathy and retinopathy of Dicentrarchus labrax and Sparus aurata farmed in Tunisia

Abstract

Viruses belonging to the Nodaviridae family cause disease worldwide among a large number of species of marine fish, and have been described in all continents. In the present study, a total of 69 farmed Tunisian sea bass (Dicentrarchus labrax) and 24 sea bream (Sparus aurata) samples were tested monthly for the detection of betanodavirus. The virus was identified in both species using indirect immunofluorescence assays (IFAT) and RT-PCR. In addition sequence analysis of part of the coat protein gene indicated that both species were infected by highly related, but distinct, strains belonging to the RGNNV genotype. The sequence of the coat protein gene of several strains was identical but up to 9 different sequences were detected in a single farm. In addition, viral sequences obtained from fish that were held at lower temperature (<20 degrees C) were distinct from the rest of the sequences.

Nodaviruses in Wild Fish Population Collected Around Aquaculture Cage Sites from Coastal Areas of Tunisia

“…Comparison of a partial sequence from the coat protein gene of the wild isolates showed a similarity ranging from 94% to 97% to the Tunisian nodaviruses retrieved from farmed sea bass and sea bream [4,24]. In addition, the similarity with the rest of the genotypes was ranging from 88% to 97% (data not shown).…”

“…In addition, the similarity with the rest of the genotypes was ranging from 88% to 97% (data not shown). All of the Tunisian isolates from farmed fish are classified as RGNNV genotype [4] however isolates from wild fish sequenced in this study could not be grouped with the RGNNV (Figure 1) unless further amplifications targeting variable RNA2 region will be conducted. The evolutionary history was inferred using the UPGMA method [25].The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) is shown next to the branches [23].…”

“…The virological survey was performed on several species of apparently healthy wild marine fish species as well as farmed sea bass. The aim of the project was to focus on the detection of healthy carriers of piscine Nodavirus due to the importance of this virus in Mediterranean and the North African aquaculture [4]. Indeed, viral nervous necrosis (VNN) has emerged to become a major problem in the culture of larval and juvenile marine fish worldwide [5].…”

“…Phylogenetic analyses [18][19][20] have revealed that genetic lineages of the Nodaviruses show low host specificity and generally correspond to geographic location. This finding suggests that genotypes have generally emerged due to spill-over from reservoirs that include a broad range of wild marine fish, although some isolates revealed links to commercial movement [4]. Currently, there exists insufficient epidemiological evidence to support the listing of VNN as endemic to fish along the Tunisian coast line.…”

Betanodavirus of Marine and Freshwater Fish: Distribution, Genomic Organization, Diagnosis and Control Measures

“…It can persist in the host for a long time sub-clinically and may cause severe mortality under extreme environmental conditions [105]. The horizontal transmission may occur from infected fish, feed, contaminated trash fish/carrier animals and contaminated water supply [18,44,47,69,87,119]. The cannibalistic nature of fish such as Asian seabass and brown-marbled grouper fingerlings may also enhance the horizontal transmission of the virus [78].…”