Toyohiko Nishizawa

Sequence of the non-structural protein gene encoded by RNA1 of striped jack nervous necrosis virus

Striped jack nervous necrosis virus (SJNNV), the causative agent of viral nervous necrosis in marine fish, is a member of the family Nodaviridae whose genome consists of two positive-sense RNA molecules encapsidated in a single virion. In this study, the nucleotide sequence of SJNNV RNA1 was determined. The SJNNV RNA1 was 3081 bases long and contained a single ORF encoding 983 aa of approximately 110 kDa. The sequence identities between RNA1 of SJNNV and RNA1 of insect nodaviruses were 28% at the nucleotide and amino acid levels, although the conserved motifs for the RNA-dependent RNA polymerase were located at almost the same positions in the amino acid sequences. The present study, together with our previous work on SJNNV RNA2, suggests that a new genus, Piscinodavirus, should be created in the family Nodaviridae.

Failure of the Polymerase Chain Reaction (PCR) Method to Detect Striped Jack Nervous Necrosis Virus (SJNNV) in Striped Jack Pseudocaranx dentex Selected as Spawners

Abstract The causative agent of viral nervous necrosis (VNN) in striped jack Pseudocaranx dentex is transmitted from female and male spawners to larvae, and elimination of carrier spawners, determined by the detection of striped jack nervous necrosis virus (SJNNV) via polymerase chain reaction (PCR), has been used to prevent transmission of the disease in larval production facilities. However, some outbreaks of VNN occurred in larvae obtained from SJNNV-negative spawners. We compared the occurrence of infection between groups of larvae obtained from SJNNV-negative spawners and those from SJNNV-positive spawners. Viral nervous necrosis occurred in all seven groups of larvae obtained from the virus-positive spawners between the 3rd and 7th day of rearing. The virus was detected only occasionally after 2 weeks in four of six groups obtained from the virus-negative spawners. These results confirmed vertical transmission of the virus and revealed that a very small amount of SJNNV in spawners escaped PCR detect...

Mapping a neutralizing epitope on the coat protein of striped jack nervous necrosis virus.

Striped jack nervous necrosis virus (SJNNV), a fish nodavirus, is the causative agent of viral nervous necrosis in marine fishes. The fish nodaviruses are divided into four different genotypes based on the nucleotide sequence of the coat protein gene. In the present study, partial coat protein genes of fish nodaviruses were expressed. This allowed the serological relationship among the different virus genotypes to be analysed and neutralizing epitopes on the coat protein to be mapped. Western blot analysis revealed that SJNNV and other fish nodavirus genotypes shared a significant number of common antigenic determinants, although SJNNV was serologically distinguishable. The results suggested that the SJNNV determinant for neutralizing MAbs was a linear epitope, which consisted of a repeated amino acid sequence within the coat protein. One of the neutralizing epitopes of SJNNV was deduced to be PAN at aa 254-256 in the coat protein.

RT-PCRによるブリからのPhotobacterium damselaの検出

魚類病原細菌 Photobacterium damsela subsp. damsela および Ph. damsela subsp. piscicida を検出するために、本菌の 16S rRNA における種特異的塩基配列の解析に基づきRT-PCR法を考案した。まず、魚介類病原菌を中心とした12種のビブリオ属細菌を用いて本RT-PCRの特異性を確認し、また検査魚の脾臓磨砕液をトリプトソーヤ・ブロスで前培養後RT-PCRに供することにより検出感度が高まることが分かった。この方法を用いることにより、外見的に健康な養殖ブリ Seriola quinqueradiata およびウマヅラハギ Thamnaconus modestus やマアジ Trachurus japonicus など数種の天然魚に Ph. damsela が存在することが明らかにされた。