Single test picks up all strains of deadly fish virus that threatens barramundi

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Exotic ISKN virus is a threat to Australian fish, particularly barramundi Lates calcarifer and now there is a new testing method which can identify all three ISKNV variants. ISKNV has three known variants but validated tests to identify the virus only pick up two of these variants.

Scientists at the University of Sydney in Australia and the University of Florida in the USA have developed a new genetic test for the infectious spleen and kidney necrosis virus (ISKNV) that is deadly in fish, affecting aquaculture and ornamental fish varieties worldwide.

New research published in PLOS One on 3 February 2023  demonstrates a single test for all three genomic variants of the virus, which can kill 50 to 100 percent of fish infected. The third variant – known as TRBIV – is an emerging pathogen and causing fish deaths in barramundi farms in Southeast Asia. While the disease caused by the virus is reportable to the World Organisation for Animal Health, TRBIV is not included in the WOAH testing requirements.

Associate Professor Joy Becker, School of Life and Environmental Sciences, University of Sydney

Associate Professor Joy Becker from the School of Life and Environmental Sciences at the University of Sydney is a corresponding author of the paper. She said: “The emerging TRBIV variant is a risk to the Australian barramundi industry.

“Our new diagnostic test is the most advanced in addressing WOAH requirements for test validation. It can detect all three variants of the virus with very high sensitivity and specificity.

“Once validated, we expect this diagnostic test will help keep this exotic virus out of Australia.”

While ISKNV has not been detected in wild fish stocks in Australia, it is regularly detected in ornamental fish in quarantine at the international border and in retail pet shops, according to the Australian Department of Agriculture.

In this article, the authors cited reports that ISKNV has been detected across a wide range of countries with a majority of the reports from Asia. Clinical signs of disease are non-specific and include lethargy, gill pallor, skin discoloration, inappetence, and abnormal swimming. These gross clinical signs in addition to subclinical infections make surveillance efforts extremely important to control the spread of this virus.

Becker added, “Exotic disease incursions are one of the biggest risks for our wild and farmed fish. The ISKN virus, which now includes the TRBIV variant, is a risk to Australian species, including barramundi and Murray cod.

“Our diagnostic test is designed to detect all three variants and provides the stringency we need to uphold Australia’s world-class biosecurity.”

Deputy Vice-Chancellor (Research) Professor Emma Johnston said, “Associate Professor Becker is an outstanding scientific leader in aquaculture and fish health.

“Working with international colleagues, her latest research is another important contribution that can help Australia – and the world – develop sustainable stewardship of our oceanic resources and support global food security.”

Becker said that while the virus is devastating for infected fish, the disease poses no risk to humans.

Citation: Koda SA, Subramaniam K, Hick PM, Hall E, Waltzek TB, Becker JA (2023) Partial validation of a TaqMan quantitative polymerase chain reaction for the detection of the three genotypes of Infectious spleen and kidney necrosis virus. PLoS ONE 18(2): e0281292.

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