Infectious Spleen and Kidney Necrosis Virus (ISKNV) in Asian Seabass
Hello all!
Today, we’re going to discuss one of the most important viral diseases that has caused significant economic losses in Asian seabass aquaculture ie. Infectious Spleen and Kidney Necrosis Virus (ISKNV). As the name suggests, this virus primarily targets the spleen and kidney of infected fish.
Asian seabass (Lates calcarifer), commonly known as barramundi, is a highly valued aquaculture species known for its excellent taste and nutritional benefits.
In India, the production of Asian seabass reached over 7,500 tonnes in 2022, with an estimated market value of USD 11.1 million, and this number is expected to rise in the coming years.
Consumer demand remains strong, especially from Europe and Australia, where the preference for large-sized seabass has been increasing due to its superior flavor and nutritional profile.
The Emerging Disease Threat
Diseases are one of the most unpredictable and serious challenges in aquaculture and ISKNV is among the deadliest.
This virus, which belongs to the genus Megalocytivirus, can cause mortality rates of up to 80–85% in farmed Asian seabass populations, leading to devastating losses for farmers.
About the Virus
Megalocytiviruses are icosahedral, double-stranded DNA viruses with circularly permuted genomes. They are capable of infecting more than 50 species of freshwater and marine fish.
The virus was first reported in China, where it caused severe mortality in mandarin fish (Siniperca chuatsi).
Genomic and histopathological analyses have revealed that ISKNV is closely related to Red Seabream Iridovirus (RSIV), with both viruses classified under the same genus, Megalocytivirus.
ISKNV also shares similarities with other viruses in the same family, including Taiwan Grouper Iridovirus, Turbot Reddish Body Iridovirus, Dwarf Gourami Iridovirus, and Rock Bream Iridovirus.
Host Range
ISKNV exhibits a wide host range, infecting both cultured and ornamental fish species such as:
Recently, ISKNV infections have also been reported in Nile tilapia, highlighting its broad host susceptibility and high transmissibility.
Infected tilapia often exhibit darkened body coloration, erratic swimming, abdominal distension, and ascites, with mortalities exceeding 50%.
Gross Signs & symptoms
Image: Gross signs of ISKNV-infected Asian seabass Source: Zhiming Zhu et al., 2021
Histopathological Observations
Microscopic examination of infected organs reveals the following changes:
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Liver: Cellular vacuolization, lymphocytic infiltration, and cell enlargement
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Spleen: Enlargement of cells (megalocytes)
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Kidney: Cellular infiltration and lymphocytic accumulation
Image: Histopathological and histochemical features of ISKNV-infected Asian seabass
Source: Zhiming Zhu et al., 2021
Transmission Pathways
Studies suggest that ISKNV enters host cells through caveola-mediated endocytosis and relies on microtubules to move through the endoplasmic reticulum pathway.
The virus can spread horizontally, from one pond to another, through infected water, equipment, or fish.
Prevention and Control
Currently, there is no effective treatment available for ISKNV infection. Therefore, prevention is the best approach, which includes:
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Using virus-free broodstock and fry
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Implementing strict biosecurity and quarantine measures
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Conducting regular health monitoring and early detection
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References:
https://doi.org/10.1016/j.aquaculture.2020.736326
https://doi.org/10.1099/jgv.0.000818
https://doi.org/10.1006/viro.2001.1208
https://doi.org/10.3354/dao058127
https://doi.org/10.1016/j.jviromet.2009.01.008
https://doi.org/10.1016/j.prevetmed.2015.09.008
https://doi.org/10.1016/j.virol.2004.05.008
https://doi.org/10.1128/JVI.06947-11
https://doi.org/10.1111/tbed.13825
https://doi.org/10.1155/2023/6643006
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