Aquaculture Magazine

Aquatic researchers say they have proven white spot outbreak in prawns came from overseas

The findings are yet to be peer reviewed or published in a scientific journal, but the group said all of the sequences were being submitted to scientific databases and made available to researchers around the world.

A group of researchers is pressuring government agencies still investigating the origins of a prawn disease outbreak, by publishing independent data they say proves the virus came to Australia on imported prawns.

But the Federal Department of Agriculture said it had not seen the scientists' data and it was still investigating the cause of the outbreak, which may never be known.

White spot disease, which can kill entire ponds of farmed prawns but is not a risk to human health, was first found on farms along the Logan River south of Brisbane in December.

The department is still investigating how it got to Australia and wiped out the local $25 million prawn farming industry, but the aquaculture industry has been quick to blame imported prawns sold in supermarkets.

To solve the mystery, the Aquaculture Genetics Research Group at the University of the Sunshine Coast has been comparing the DNA of white spot-infected prawns in Australia to overseas prawns, and finding genetic matches.

"The sequences show there is a very close similarity with the Australian white spot sequences with those reported internationally," associate professor Wayne Knibb said.

"In fact they are so close that it really excludes the possibility that we have had a long-term species of white spot living in Australia waters which recently jumped to the farms.

"The sequences are too close to the international ones, and it looks like the best explanation is we had a point source outbreak of a few varieties, or even only one."

Department 'welcomes' test data

A departmental spokesman said the department would welcome detailed information and test data from researchers.

"University of the Sunshine Coast researchers have not made the methodology or data associated with this report available to the department," he said.

"The department is unable to provide an informed comment on these assertions.

What is white spot virus?

Prawn with white spot disease

White spot disease in prawns is highly contagious, lethal to crustaceans and has reduced prawn farm productivity by up to 40 per cent overseas.

"It is important to understand that confirming the origin of white spot virus does not demonstrate the pathway for the cause of the outbreak.

"The department has investigated a number of possible pathways, and while it is possible some of these will be better understood with further analysis, the definitive cause may never be known."

Despite the work already done by the researchers using DNA sequencing to link the Australian outbreak to international strains of the virus, the spokesman said the department was still pursuing a number of lines of inquiry, including genetic analysis.

"To identify if there is a link between infected prawns found in Australia and overseas strains of white spot disease," he said.

"This may shed some light on the origins of the outbreak.

"Overseas strains of white spot could enter the country through a number of different pathways, including the misuse of imported prawns for human consumption, broodstock, infected feed or probiotics or contaminated equipment."

Prawn farms in south east Queensland along the Logan River have all been wiped out due to a disease outbreak

White spot disease wiped out all seven prawn farms in south-east Queensland, and led to bans on imports of green prawns. (ABC Rural: Marty McCarthy)

Origins may never be known

Federal Agriculture Minister Barnaby Joyce has previously told the ABC white spot could have come in to Australia on infected prawns in bilge water, or could have been in Australia for a while.

A recent history of biosecurity outbreaks

 Varroa mite

Outbreaks of tomato potato psyllid, chestnut blight and cucumber green mottle mosaic virus are among those having an impact on Australia's horticulture industry.

In an interview with the ABC in March, Mr Joyce also said "there was no direct link between prawns at a retail level and the white spot outbreak".

The Department of Agriculture has revoked import permits from six importers who brought contaminated prawns to Australia, but there is no suggestion those prawns caused the outbreak.

During a Senate Estimates hearing last month, department officials suggested the origins may never be known.

However, Dr Knibb said the findings from the research group would put pressure on the department to be more forthcoming with any data it had relating to the origins of the outbreak, or to be more thorough in its investigation.

"We are a university and our job is to produce knowledge. We are not necessarily constrained by the political implications of that knowledge," he said.

Authorities urged to acknowledge source

Dr Knibb urged authorities to put politics aside so the aquaculture industry could safeguard itself against future biosecurity threats.

"In terms of possible implications, yes, of course there will be [political] implications with the knowledge of how white spot got into Australia," Dr Knibb said.

"But there is a balance, presumably, at government levels between public disclosure and the good that the public disclosure of knowledge achieves."

Dr Knibb said authorities had access to the same technology as his team, and should also be able to trace the outbreak back to a source country.

"There is always subtle differences in technology and procedures, but fundamentally, a state would process the capabilities to do the same sort of sequencing we have done," he said.

"They also should have more financial resources to do a wider range of samples."

However, Dr Knibb admitted that government agencies needed to be absolutely certain of the data before they could categorically conclude the disease came from prawn imports.

"If they haven't been able to find mathematical certainty that connects an origin to the outbreak, then they don't want to release it," he said.

The findings are yet to be peer reviewed or published in a scientific journal, but the group said all of the sequences were being submitted to scientific databases and made available to researchers around the world.

"We are confident enough of our data to provide a hypothesis for the best working model, one that we are fairly certain of, that it came from overseas," Dr Knibb said.

Source: http://www.abc.net.au/news/rural/2017-06-19/white-spot-research-blames-imported-prawns/8629918

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