Iridovirus is a causative agent of epizootics among cultured rock bream (Oplegnathus fasciatus) in Korea. Here, we report the complete genomic sequence of rock bream iridovirus (RBIV). The genome of RBIV was 112080 bp long and contained at least 118 putative open reading frames (ORFs), and its genome organization was similar to that of infectious spleen and kidney necrosis virus (ISKNV). Of the RBIV's 118 ORFs, 85 ORFs showed 60-99% amino acid identity to those of ISKNV. Phylogenetic analysis of major capsid protein (MCP), DNA repair protein RAD2, and DNA polymerase type-B family indicated that RBIV is closely related to red sea bream iridovirus (RSIV), Grouper sleepy disease iridovirus (GSDIV), Dwarf gourami iridovirus (DGIV), and ISKNV. The genome sequence provides useful information concerning the evolution and divergence of iridoviruses in cultured fish.

Ten iridoviruses were isolated from cultured fish from various regions in Korea; 7 from rock bream, 1 from red sea bream, 1 from sea bass, and 1 from rockfish. The full open-reading frame (ORF) encoding the major capsid protein (MCP) (1362 bp) from ten iridoviruses were sequenced and the nucleotide sequences were phylogenetically analyzed. Phylogenetic analysis revealed that the ten Korean isolates were classified into one cluster. However, their sequences were not identical and, based on the nucleotide sequence variation, they could be further divided into two subgroups. While nine Korean isolates were similar to the Japanese isolate red sea bream iridovirus (RSIV), one isolate was distinct from other iridovirus isolates. These results suggest that a diversity of iridoviruses exist in Korea and that a new variant strain has emerged.

In 2003, 13 isolates of iridovirus were obtained from cultured flounders Paralichthys olivaceus during epizootics in Korea. The full open reading frames (ORFs) encoding the major capsid protein (MCP) (1362 bp) from the 13 flounder iridoviruses (FLIVs) were sequenced and the deduced amino acid sequences were phylogenetically analyzed. Phylogenetic analysis of the MCP revealed that all 13 FLIVs were the same species as rock bream iridovirus (RBIV), red sea bream iridovirus (RSIV), and infectious spleen and kidney necrosis virus (ISKNV), and were grouped into an unknown genus which was different from the 2 genera known to infect fish, Ranavirus and Lymphocystivirus. This is the first report on the isolation and phylogenetic analysis of the iridovirus of unknown genus from flounders during epizootics.

Since the publication of the first report on fish nodaviruses in Korea in 1998(Sohn et al. 1998 J Fish Pathol 11:97-104), fish nodaviruses have caused widespread epizootic events among various fish species in Korea. However, the genotypes of fish nodaviruses in Korea have not yet been determined due to a lack of information about their nucleotide sequences. In this study, we isolated 5 fish nodaviruses from 4 fish species cultured in 4 different regions in Korea: rock bream Oplegnathus fasciatus, Japanese flounder Paralichthys olivaceus, sevenband grouper Epinephelus septemfasciatus, and grey mullet Mugil cephalus. The full open-reading frame (ORF) encoding the coat protein (1017 nt) was sequenced from each of the 5 fish nodaviruses and the nucleotide sequences were phylogenetically analyzed. Results showed that even though their sequences were not identical, all 5 Korean isolates were clustered in the RGNNV genotype. This is the first report on the phylogenetic analysis of fish nodaviruses from cultured fish in Korea. KEY WORDS: Fish nodavirus · Coat protein · Phylogenetic analysisResale or republication not permitted without written consent of the publisher

Since 2010, several strains of Duck Tembusu Virus (DTMUV) have been isolated from China. In autumn 2021, high mortality was observed in southwestern Guizhou Province, China, and a DTMUV strain named GZSS2022 was successfully isolated. After inoculation with SPF chicken embryos of 10 days age, the embryos died 3-5 days after inoculation, and RT-PCR could still detect DTMUV positive after collecting the allantoic fluid of dead chicken embryos and transmitting it for 4 generations. In addition, the GZSS2022 strain was able to replicate in BHK-21 cells and induce cytopathic effects (CPE), and the virus particles were observed in the cytoplasm by transmission electron microscopy. In animal experiments, GZSS2022 strain can replicate stably and pathological examination results showed that the brain of infected ducks was congested and vascular sheath formed around the blood vessels; Liver lymphocyte infiltration, necrosis, liver bleeding. The E gene of this strain was sequenced by PCR and its homology and genetic evolution were analyzed. It was found that the homology of GZSS2022 with the Beijing duck reference strain (MT108699.1) was the highest 99.39%, and the homology of GZSS2022 with the early isolated reference strain (FX2010) was 96.88%. The GZSS2020 strain was located in the same subbranch as the reference strain from Beijing duck in China. The results of this study indicate that a novel highly virulent Tambusu virus has appeared for the first time in Guizhou Province, China, and further lay the foundation for the study of the pathogenicity and host range of this novel Tambusu virus.