A mixed infection in sevenband grouper Epinephelus septemfasciatus affected with viral nervous necrosis (VNN)

• Published in: Aquaculture Vol. 284; no. 1; pp. 41 - 45
• Main Authors: Kokawa, Yuki, Takami, Ikuo, Nishizawa, Toyohiko, Yoshimizu, Mamoru
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-11-2008; Amsterdam: Elsevier Science; Elsevier
• Subjects: Animal aquaculture; Animal productions; Betanodavirus; Biological and medical sciences; brain; disease control; Epinephelus; Epinephelus septemfasciatus; fish culture; fish diseases; Fish nodavirus; Fundamental and applied biological sciences. Psychology; General aspects; grouper; immunization; lethal dose; Marine; Microbiology; Mixed infection; mortality; Nodavirus; pathogenicity; RGNNV; vaccination; Vaccine; viral diseases of animals and humans; Viral nervous necrosis; viral nervous virus; Virology; virulence; VNN; Japan; INW, Japan, Kyushu, Nagasaki Prefect; Fish nodavirus; Viral nervous necrosis; Vaccine; Mixed infection; RGNNV; VNN; Necrosis; Virus; Vertebrata; Pisces; Nodaviridae; Nodavirus; Aquaculture
• ISSN: 0044-8486; 1873-5622
• DOI: 10.1016/j.aquaculture.2008.07.026

Viral nervous necrosis (VNN) of groupers by fish nodavirus is one of the most serious diseases in aquaculture around the world. In the present study, we introduced a mixed infection of fish nodavirus with another filterable pathogen(s) in VNN-affected sevenband grouper of Nagasaki Prefecture, Japan. In challenge tests with the brain-homogenate of VNN-affected grouper, relative percent survival (RPS) of fish immunized with inactivated brain-homogenate was 95%, but that of fish with inactivated RGNNV, which was isolated from the VNN-affected grouper, was only 28%, although the same degree of RGNNV antigens were included in both of the immunized materials. Although 50% lethal dose (LD
50) of RGNNV was 10
3.5 TCID
50/100 µl/fish, an inoculum of the VNN-affected grouper brain-homogenate with LD
50 against sevenband grouper contained only 10
1.5 TCID
50/100 µl. Infectivity titer of RGNNV was not influenced by Triton X-100 (TrX) treatment, but cumulative mortalities of fish inoculated with non- and TrX-treated brain-homogenate of VNN-affected fish were 70% and 40%, respectively, meaning that virulence of the brain-homogenate distinctly decreased by TrX-treatment. Therefore, it was suggested that a TrX-sensitive virus(es) participating fish mortality existed as a mixed infection with RGNNV in VNN-affected sevenband grouper of Nagasaki Prefecture, Japan.