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Diseases of Aquatic Organisms

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DAO 79:199-205 (2008)  -  DOI:

Variable region of betanodavirus RNA2 is sufficient to determine host specificity

Yu Ito1,2, Yasushi Okinaka1,*, Koh-Ichiro Mori3, Takuma Sugaya3, Toyohiro Nishioka4, Masakazu Oka5, Toshihiro Nakai1

1Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan
2Graduate School of Life and Environmental Sciences, Tsukuba University, Tsukuba 305-8577, Japan
3National Research Institute of Aquaculture, Fisheries Research Agency, Saiki 879-2602, Japan
4National Research Institute of Aquaculture, Fisheries Research Agency, Minami-Ise 516-0193, Japan
5Management Section of National Center for Stock Enhancement, Fisheries Research Agency, Yokohama 220-6115, Japan
*Corresponding author. Email:

ABSTRACT: Betanodaviruses, the causative agents of viral nervous necrosis in marine fish, have bipartite positive-sense RNA genomes. The viruses have been classified into 4 distinct types based on nucleotide sequence similarities in the variable region (the so-called T4 region) of the smaller genomic segment RNA2 (1.4 kb). Betanodaviruses have marked host specificity, although the primary structures of the viral RNAs and encoded proteins are similar among the viruses. We have previously demonstrated, using reassortants between striped jack nervous necrosis virus (SJNNV) and redspotted grouper nervous necrosis virus (RGNNV), that RNA2, which encodes the coat protein, strictly controls host specificity. However, because RNA2 is large, we were unable to propose a mechanism underlying this RNA2-based host specificity. To identify the RNA2 region that controls host specificity, we constructed RNA2 chimeric viruses from SJNNV and RGNNV and tested their infectivity in the original host fish, striped jack Pseudocaranx dentex and sevenband grouper Epinephelus septemfasciatus. Among these chimeric viruses, SJNNV mutants containing the variable region of RGNNV RNA2 infected sevenband grouper larvae in a manner similar to RGNNV, while RGNNV mutants containing the variable region of SJNNV RNA2 infected striped jack larvae in a manner similar to SJNNV. Immunofluorescence microscopic studies using anti-SJNNV polyclonal antibodies revealed that these chimeric viruses multiplied in the brains, spinal cords and retinas of the infected fish, as in infections by the parental viruses. These results indicate that the variable region of RNA2 is sufficient to control host specificity in SJNNV and RGNNV.

KEY WORDS: Betanodavirus · Host specificity · Viral nervous necrosis · Chimeric virus · RNA2 · T4 region · SJNNV · RGNNV

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Cite this article as: Ito Y, Okinaka Y, Mori KI, Sugaya T, Nishioka T, Oka M, Nakai T (2008) Variable region of betanodavirus RNA2 is sufficient to determine host specificity. Dis Aquat Org 79:199-205.

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