Pathogenicity of Different Betanodavirus RGNNV/SJNNV Reassortant Strains in European Sea Bass

Abstract

European sea bass (Dicentrarchus labrax) is an important farmed marine species for Mediterranean aquaculture. Outbreaks of betanodavirus represent one of the main infectious threats for this species. The red-spotted grouper nervous necrosis virus genotype (RGNNV) is the most widely spread in Southern Europe, while the striped jack nervous necrosis virus genotype (SJNNV) has been rarely detected. The existence of natural reassortants between these genotypes has been demonstrated, the RGNNV/SJNNV strain being the most common. This study aimed to evaluate the pathogenicity of different RGNNV/SJNNV strains in European sea bass. A selection of nine European reassortants together with parental RGNNV and SJNNV strains were used to perform in vivo experimental challenges via intramuscular injection. Additional in vivo experimental challenges were performed by bath immersion in order to mimic the natural infection route of the virus. Overall, results on survival rates confirmed the susceptibility of European sea bass to reassortants and showed different levels of induced mortalities. Results obtained by RT-qPCR also highlighted high viral loads in asymptomatic survivors, suggesting a possible reservoir role of this species. Our findings on the comparison of complete genomic segments of all reassortants have shed light on different amino acid residues likely involved in the variable pathogenicity of RGNNV/SJNNV strains in European sea bass.

Reassortant viruses threatening fish aquaculture

“…In vivo challenges have shown that European sea bass juveniles are much more susceptible to RGNNV than to SJNNV, correlating with European sea bass well‐known susceptibility and in vitro studies. Interestingly, different RGNNV/SJNNV strains produced intermediate mortalities, 34,60–62 again as in the in vitro study, 59 whilst SJNNV/RGNNV strain produce roughly the same mortality as the SJNNV one. This variability emphasizes the relevance of possible point mutations in the virulence of reassortant strains.…”

Redspotted Grouper Nervous Necrosis Virus and the Reassortant RGNNV/SJNNV In Vitro Susceptibility against a Commercial Peroxy-Acid Biocide under Different Conditions of Use

“…Overall, these viral features influence important biological characteristics, such as host range, pathogenicity, and antigenic properties [ 10 , 33 , 34 ]. Recently, NNV coat-protein structure prediction showed that amino acid substitutions could play a role in affecting the hydrophobicity varying in the SJNNV, RGNNV, and reassortant strains [ 35 ]. This study focuses on the relationship between amino acid sequence charge and strain virulence; however, a change in the amino acid chemical characteristics could also affect the disinfectant’s effectiveness against the two tested viral strains.…”

Advances in Viral Aquatic Animal Disease Knowledge: The Molecular Methods’ Contribution

“…Moreover, the recent application of whole genome sequencing (WGS) to the study of aquatic viruses is gaining importance due to the large amount of information that it could generate. Accordingly, the WGS has permitted the identification of variable amino-acid residues probably correlated to the NNV virulence and pathogenicity thanks to the analysis of the NNV reassortant strains’ RdRp and capsid protein physico-chemical characteristics [ 162 ]. In particular, the amino acids (aa) 247 and 270 of capsid protein have been identified as putative viral receptor binding sites; accordingly, substitutions at these positions could affect the virus–host interaction.…”

“…In particular, the amino acids (aa) 247 and 270 of capsid protein have been identified as putative viral receptor binding sites; accordingly, substitutions at these positions could affect the virus–host interaction. In addition, Biasini and colleagues [ 162 ] speculated on the potential existence of additional interesting residues that are all exposed on the outside of the structure of the trimeric P-domains. In particular, seven variable amino acids were identified and it was possible to speculate using protein-structure prediction that changes in these positions alter the hydrophobicity and the steric hindrance of the exposed surface region, changing the physiochemical properties of the capsid protein.…”