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

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.