Characterization and immunological studies of fish nervous necrosis virus

Abstract

An icosahedral virus with a mean diameter of 28-30 nm, isolated from a diseased marine fish, grouper, Epinephelus tauvina (ETNNV) was cultured in sea bass (SB) cell line, characterized, and its pathogenicity studies were carried out. Electron microscopy revealed that this virus replicates exclusively in the cytoplasm and forms paracrystalline array and inclusion bodies in the infected cells. SDS-PAGE analysis of structural proteins of the purified virus resolved one major polypeptide of approximately 42 kDa. Upon infection on SB cells it induces typical cytopathic effects such as rounding and granulation of cells, localized cell death and detachment of cells. The genome organization of this virus showed its close similarity to fish nervous necrosis viruses and its distant relation to insect nodaviruses. Therefore, based on the morphological, biochemical and genomic characteristics of this virus it was classified as a member of the genus Alphanodavirus in the family Nodaviridae. This virus induces typical viral nervous necrosis in the experimentally-infected sea bass larvae. Using the SB cell culture and RT-PCR, a closely related nervous necrosis virus was isolated from a diseased freshwater ornamental fish guppy, Poicelia reticulata. This virus was also characterized and its similarities with the ETNNV were studied. Experimental infection using these two viral isolates in guppy fry showed asymptomatic infection. Immunological studies were carried out to evaluate the immune response of guppy, and gouramy, Trichogaster tricopterus towards the E. coli expressed recombinant coat protein of ETNNV. In vitro neutralization of virus infectivity with anti-ETNNV recombinant coat protein antisera raised in gouramy, guppy and rabbit suggested that the recombinant coat protein of ETNNV can be used as candidate vaccine in fish.