Viruses are known as serious pathogens, which can cause severe disease sea
fish diseases, especially red seabream iridovirus (RSIV), viral haemorrhagic septicaemia
virus (VHSV), viral nervous necrosis virus (VNNV), marine birnavirus (MABV)
and hirame rhabdovirus (HRV). VHSV has been a serious viral disease that infects
the olive flounder in South Korea. Clinical signs of VHSV infection are skin darkening,
abdominal distension and haemorrhages. Outbreaks of fish iridovirus disease was
first reported from red seabream, Pagrus major farms in Japan. Recently, iridovirus
infection have occurred frequently from olive flounder farms in South Korea. VNNV
is a worldwide viral disease affecting several species of cultured sea fish such as
olive flounder in South Korea. MABV is also causes serious problems in the olive
flounder farming industry in Japan. The infectious marine birnavirus are well
known fish pathogens in Asian countries such as Korea and China (olive flounder
farm). The initial case of HRV was reported from olive flounder farms in Japan.
Since then, HRV infections with severe mortalities have occurred at olive flounder
farms in South Korea.
In this study, disease surveillance was performed to monitor the prevalence of
viral diseases in olive flounder from 2014 to 2015. The fish samples were collected
from 60 different farms of Jeju in April, May, September, November and December
2014. In 2015, the fish samples were collected in March (60 farms), May (55 farms),
July (52 farms) and October (53 farms) from different farms. RT-PCR or PCR results
showed that VHSV were detected in 7 farms (2014-5, 2015-2). In addition, the
suspected of viral disease were detected by PCR with each specific primers.
RT-PCR or PCR results showed that VHSV were detected in 8 farms (2014-5,
2015-3), but other viral diseases have not been detected in any farms.
The sequences of the nucleocapsid protein (N) gene and glycoprotein (G) gene
of 15 VHSV isolates were successfully amplified and sequenced. Phylogenetic analysis
was performed using the VHSV sequences reported here together comparison
with the nucleotide sequences available from the GenBank database. Phylogenetic
analysis indicated that most of Korea VHSV belong to the genotype Ⅳa and closely
related to the strains from Japan and China.