Phylogenetic Analysis of Betanodavirus RNA2 Identified from Wild Marine Fish in Oceanic Regions

Abstract

ABSTRACT-Betanodaviruses, the causative agents of viral nervous necrosis of fish in aquaculture, can be genetically classified into four types, designated SJNNV, RGNNV, TPNNV and BFNNV. To investigate betanodaviruses in apparently healthy wild fish, we tested 20 fish species from some surrounding ocean areas of Japan for the detection of viral RNA using PCR-based methods. Of 729 fish tested, six (six species) and 87 (11 species) samples were positive for RT-PCR and nested PCR, respectively. These positive species have never been reported as susceptible hosts. Sequencing of obtained PCR amplicons revealed that RGNNV and SJNNV existed in nine and six fish species, respectively. BFNNV was found from one species, round herring Etrumeus teres. Interestingly, the RNA2 sequences thus obtained had more variations than those from wild fish caught around aquaculture facilities in our previous report. These results suggest that genetically varied betanodaviruses are widely spread around Japan.

Cell Culture Isolation of Piscine Nodavirus (Betanodavirus) in Fish-Rearing Seawater

“…However, there has been no direct evidence for this hypothesis. Molecular analyses have indicated the presence of different betanodaviruses with high numbers of sequence variations or reassortant viruses in populations of wild fish compared with those isolated from diseased fish, which have relatively limited sequence variations (52). The virulent forms of these viruses may have originated from less-susceptible wild fish and subsequently shed in water, or various genetic variants may have been present as virions in water and only virulent forms infected susceptible cultured fish.…”

Mortality due to viral nervous necrosis in zebrafish Danio rerio and goldfish Carassius auratus

“…2). The specific rt-PCR amplified the variable region of viral RNA2, which has extensively been used to infer the relatedness and phylogeny of betanodavirus (Nishizawa et al 1997, Sakamoto et al 2008. Nucleotide sequencing of PCR products followed by BLAST analysis confirmed the origin of the sequence to betanodavirus with high similarity hits (97−98%).…”

Pathogenicity of Striped Jack Nervous Necrosis Virus (SJNNV) Isolated from Asymptomatic Wild Japanese Jack Mackerel <i>Trachurus japonicus</i>

“…Our previous study (Sakamoto et al, 2008), in which apparently healthy wild Japanese jack mackerel (n=110) caught in three surrounding ocean areas of Japan were examined, showed that betanodaviruses (SJNNV or RGNNV) were detected at rates of 0% and 30% in RT-PCR and nested PCR, respectively, but neither SJNNV nor RGNNV were isolated with E-11 cells. Because of this experience, we anticipated that the virus in asymptomatically infected wild fish is either less virulent to fish or less invasive to cells, and thus, it may be difficult to isolate this type of virus with cultured cells.…”

“…Many studies have reported that the genomes of betanodaviruses, except for the TPNNV genotype, were detectable by PCR-based methods in a variety of wild marine fish species, including valuable feed fish (Sano et al, 2011). This suggested that wild fish could be a possible source of the virus in mortalities of cultured fish (Barker et al, 2002;Gomez et al, 2004;Sakamoto et al, 2008). However, direct evidence for such dietary or horizontal transmission of the virus is lacking, partly due to the difficulty of isolating betanodaviruses from subclinically infected wild fish (Sakamoto et al, 2008).…”

“…This suggested that wild fish could be a possible source of the virus in mortalities of cultured fish (Barker et al, 2002;Gomez et al, 2004;Sakamoto et al, 2008). However, direct evidence for such dietary or horizontal transmission of the virus is lacking, partly due to the difficulty of isolating betanodaviruses from subclinically infected wild fish (Sakamoto et al, 2008).…”