Water temperature affects pathogenicity of different betanodavirus genotypes in experimentally challenged Dicentrarchus labrax

Abstract

Betanodaviruses are the causative agents of a highly infectious disease of fish known as viral nervous necrosis (VNN). To date, 4 different nervous necrosis virus (NNV) genotypes have been described, but natural reassortant viruses have also been detected, which further increase viral variability. Water temperature plays an important role in determining the appearance and the severity of VNN disease. We assessed the effect of temperature (20°, 25° and 30°C) on mortality and virus load in the brain of European sea bass Dicentrarchus labrax experimentally infected with 4 genetically different betanodaviruses, namely red-spotted grouper NNV (RGNNV), striped jack NNV (SJNNV) and the reassortant strains RGNNV/SJNNV and SJNNV/RGNNV. The RGNNV/SJNNV virus possesses the polymerase gene of RGNNV and the coat protein gene of SJNNV, and vice versa for the SJNNV/RGNNV virus. The obtained results showed that the RGNNV strain is the most pathogenic for juvenile sea bass, but clinical disease and mortality appeared only at higher temperatures. The SJNNV strain is weakly pathogenic for D. labrax regardless of the temperature used, while virus replication was detected in the brain of survivors only at 20°C. Finally, reassortant strains caused low mortality, independent of the temperature used, but the viral load in the brain was strongly influenced by water temperature and the genetic type of the polymerase gene. Taken together, these data show that nodavirus replication in vivo is a composite process regulated by both the genetic features of the viral strain and water temperatures.

Viral encephalopathy and retinopathy in aquaculture: a review

“…; Toffan et al . ). However, it was also recently described in some fish species cultured in southern Europe such as Senegalese sole Solea senegalensis in Spain, gilthead sea bream Sparus aurata and European sea bass in the Iberian Peninsula (Thiéry et al .…”

“…; Toffan et al . ). A strain belonging to the RGNNV species caused mass mortality in white sea bass Atractoscion nobilis reared in South California in 1999 (Curtis et al .…”

“…; Toffan et al . ; see also Phylogenetic relationships paragraph). Phylogenetic analysis of betanodaviruses was also performed based on the T2 region, which covers a larger RNA2 sequence than T4 (Chi, Shieh & Lin ; Johansen et al .…”

Viral nervous necrosis in gilthead sea bream (Sparus aurata) caused by reassortant betanodavirus RGNNV/SJNNV: an emerging threat for Mediterranean aquaculture

“…In the cohabitation experiences performed in farm 2, virus- positive survivors were unable to transfer the virus to bigger sea bream and to sea bass. Indeed, the expected resistance of this latter species to the reassortant RGNNV/SJNNV may account for the lack of transmission of the disease1617. However, for the bigger cohabitating sea bream, this could be due to the higher resistance of elder fish or to the reduced infectivity of the survivors after the acute phase.…”

“…It is worth mentioning how different viral species show diverse phenotypic features, including temperature dependency, mainly regulated by the RNA11011, as well as species tropism and immunoreactivity, determined by the RNA291213. As a result, betanodavirus pathogenicity is influenced by both environmental conditions and host species1415161718.…”