Aquaculture Magazine

White spot disease DNA found in supermarket seafood products

White spot disease in giant black tiger prawn, showing classic white spots on the carapace. 

A Queensland academic is warning that lifting a ban on the importation of green prawns into Australia is "fraught with danger" and like "playing with fire".

Since last November, seven prawn farms on the Logan River have been effectively shut down after testing positive to the devastating white spot virus.

On July 6 this year, the Federal Government ended a six-month ban on uncooked prawns coming into the country.

But University of the Sunshine Coast (USC) associate professor, Wayne Knibb, said the DNA sequence of the highly contagious white spot disease has been found in all but one of 15 frozen retail items from local supermarkets researchers tested in recent weeks.

White spot DNA found in supermarket purchases

White spot disease is a highly contagious virus lethal to crustaceans that has reduced prawn productivity overseas by up to 40 per cent.

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 has not been found harmful to human health.

On Wednesday, Dr Knibb presented the results of the USC Aquaculture Genetics Research Group testing to the Australian Prawn Farmers symposium on the Gold Coast, telling delegates the affected products had been imported from Vietnam, Thailand and China.

"When we started looking for samples to test, there were no green prawns left at the deli section," Dr Knibb said.

"But they still stocked, in the frozen section, many different varieties of imported prawns — processed prawns that ended up in spring rolls, yum cha or marinara mixes — and these were the samples that we targeted for testing.

"To our surprise, all but one of them was positive for the way we tested using PCR (polymerase chain reaction) and DNA sequencing.

"The one that was negative may have been a sample that maybe didn't really have prawn material in it."

He said the team found the white spot DNA sequence not only in packages that required cooking but in those that had already been partially pre-cooked.

"Finding the DNA doesn't necessarily mean there's an infected virus particle in these foods," Dr Knibb said.

"But it does mean that at some point in history, these animals did have infected virus.

"Our concern is if there's some error, some mistake in the cooking process or the production process, then we are going to have an opportunity for a living virus to pass into Australia."

'One hundred per cent testing' says government

In June, the Department of Agriculture and Water Resources said: "All future imports of uncooked prawns — including marinated, breaded, battered and crumbed prawns — will be subject to 100 per cent inspection [for white spot disease and a separate virus called yellowhead disease] at the border to ensure they comply with our import conditions."

White spot disease in giant black tiger prawn, showing classic white spots on the carapace.

White spot disease in giant black tiger prawn, showing classic white spots on the carapace. (Supplied: DV Lightner, Australian Government)

The statement went on to say that "high-risk products, including uncooked prawns, marinated prawns and Australian prawns processed overseas outside an approved government supply chain", would be subject to 100 per cent testing at the border.

"Only those prawns that pass testing [for both white spot and yellowhead disease] will be released from biosecurity control," the statement said.

But Dr Knibb has questioned the official government statement.

"That's not possible — to test 100 per cent. All one can do is to take a sample from a container-load [and] a container-load has tonnes and tonnes of prawns," he said.

"They can test a few, half a dozen or so, so they'll do spot sampling [but] that doesn't mean we know with certainty that white spot is not in that container.

"As long as we have a possible pathway, a possible route of infection, then one day it's going to happen and then we have to multiply that possibility, that risk, by consequence and we've seen the risk is absolutely devastating.

"Many, many families are now without jobs, there are farms that have ceased production, we've lost 20 per cent of our national prawn farm industry. So, huge risks."

Future-proofing industries at threat

Dr Knibb said as many of 50 per cent of the products his team tested were purchased after the import suspension was ended on July 6.

"Some products that we tested were in the shops as little as a week ago," he said.

"Ideally, and it may be not possible, we would like to see mechanisms that future-proofs our industries from the threat of invasive species.

"For example, every prawn product coming in should be cooked. I think these policies apply for chicken and some other imported materials, but that would be a good starting point.

"Opening up the importation of green prawns again is just playing with fire."

The Federal Department of Agriculture and Water Resources said in a statement that it was reviewing all prawn import conditions, but does not consider highly processed prawn products to be enough of a risk to be tested at the border.

It said while the products may test positive for white spot syndrome virus, they are unlikely be diverted to bait or aquaculture feed where they could cause a white spot outbreak.

Testing is tougher for raw product.

"All uncooked prawns, marinated prawns and Australian prawns processed overseas through a non-approved supply chain are required to be tested pre-export and on-arrival for white spot syndrome virus and yellow head virus."

The statement said while that, while was aware of the USC testing at retail outlets, it would welcome more detailed information as the university's researchers had not made their methodology or test data available.

Source: http://www.abc.net.au/news/rural/2017-08-02/white-spot-disease-dna-found-in-supermarket-seafood-products/8767422


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