Fish Iridoviral Disease
Iridoviruses are large cytoplasmic DNA viruses with an icosahedral morphology. The genome is both circularly permutated and terminally redundant, which is a unique feature among eukaryotic virus genomes. Based on the index of viruses database of the International Committee on Taxonomy of Viruses (ICTV) the Iridoviridae family is divided into four genera including Iridovirus, Chloriridovirus, Ranavirus, and Lymphocystisvirus.
While iridoviruses belonging to the genus Lymphocystisvirus cause the development of clusters of extremely hypertrophied fibroblasts or osteoblasts called lymphocystis cells, other iridoviruses belonging to the genus Ranavirus cause systemic disease in infected animals and are associated with high morbidity and mortality
Recently, iridoviral epizootics have frequently occurred among cultured fish in Korea.
Korean isolates were similar to the Japanese isolate RSIV and one to the Chinese isolate
ISKNV, the other Korean isolates were distinct from other foreign iridovirus isolates.
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Rock bream infected with iridovirus.
A; Darkness of the body color , B; Congested eye, C; Congested internal organs, D; Enlarged spleen.
Electron micrograph showing virions (120-130 nm in diameter) in the
cytoplasm of infected cells from the spleen of diseased fish. Bar is 100 nm.
Fish Nodaviral Disease
Fish nodaviruses are the causative agents of viral nervous necrosis (VNN) or viral encephalopathy and retinopathy in more than 30 fishspecies throughout the world. Fish nodaviruses were identified as a group of neuropathogenic viruses belonging to the family Nodaviridae, clearly distinguishable from insect nodavirus, alphanodavirus, and lately classified in the genus betanodavirus. These viruses are spherical, non-enveloped and about 25 nm in diameter and consist of a single coatprotein and a bisegmented genome, RNA1 and RNA2.
Molecular phylogeneticanalysis of the partial coat protein gene showed that fish nodaviruseswere classified into four different genotypes: SJNNV; tigerpuffer NNV (TPNNV); barfin flounder NNV (BFNNV); and redspottedgrouper NNV (RGNNV) types.
In 1998, fish nodavirus was firstly reported from sevenband grouper by Sohn et al. in Korea. Since then, high mortality caused by fish nodavirus infection has frequently occurred among cultured fish in Korea.
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Fish infected with nodavirus. A: Cerebral hemorrhage in a juvenile founder. B: Retinula necrosis in grouper.
C: Electron micrograph of virion in nodavirus-infected SSN-1 cell. Bar, 50nm.
Viral Hemorrhagic Septicemia
Viral hemorrhagic septicemia virus (VHSV), is fish rhabdovirus which cause the most economically serious viral diseases for the salmonid fish farming industry and some marine fishes in Europe and North America.
In most cases, the origin of these outbreaks could be traced back to the fish farms supplying trout to the seawater farms. The VHS outbreaks in farmed turbot (Scophthalmus maximus) in Germany in 1991 and in Scotland in 1994and the isolation of VHSV from haddock (Melanogrammus aeglefinus) and cod (Gadus morhua) caught close to the Shetland Islands in 1993 and 1995, were indications of the presence of VHSV in a wider range of fish species from the marine environment.
Since 2001, from winter to spring, an unknown viral disease has become a
popular problem in farmed Oliver flounder (Paralichthys olivaceus) of Korea. This virus caused mass mortality in fish farmed in Korea.
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Diseased olive flounder, Paralichthys olivaceus. A: Naturally diseased small fish showed rectal hernia,
B: Expanded abdomen due to ascites and the congested liver. C:Electron micrograph of virion in VHSV infected EPC cells.
Bar 100nm.