Parasite not in wild oysters

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DESPITE mistakenly reporting the presence of an oyster parasite in the Foveaux Strait, the agency in charge of the response has said there is no reason to doubt the testing that led to the removal of Big Glory Bay farms in 2017.

Biosecurity New Zealand announced in March Bonamia ostreae had been found in a routine test of wild oysters in Foveaux Strait.

But last week, it said the positive result was incorrect.

It originally announced three wild oysters had tested positive for the parasite, which can increase mortality in the bivalve.

No further oysters tested positive.

The agency apologised last Tuesday and said it would strengthen its testing processes after a review found human error contributed to incorrectly interpreted results being reported.

Readiness and response director John Walsh explained it was an internal communication issue, not an issue with the testing itself, and that no taxpayer money had been wasted on the response.

“The tests are internationally recognised.

“The mistake was human error in the chain of communication between our laboratory and our operational staff.

He said it was, in part, due to the complex nature of the process.

The three steps were an initial “screening” PCR test by Niwa; a repeat of the same type of PCR test by Biosecurity New Zealand’s Animal Health Laboratory (AHL) as used by Niwa; and then a third confirming test using AHL’s own PCR methodology.

When the series of tests was combined, it produced an inconclusive result, but was incorrectly reported as positive.

“When we identified the reporting error, affected samples were sent to Australia’s national animal health laboratory for further testing.”

Further negative results enabled Biosecurity NZ to be comfortable there was no reliable evidence of the parasite in Foveaux Strait oysters.

As a result, he said it had put in place a process to ensure a feedback loop between operational and lab staff to ensure the understanding of results was correct.

It would effectively triple-confirm results.

Biosecurity NZ was reviewing and simplifying laboratory reporting communications to ensure reports were as clear as possible and was working with the Niwa team on an end-to-end review of the process.

Despite the error, however, he said no money was wasted.

The actions taken would have been carried out with both an inconclusive or a positive result.

Strait fishery is hugely significant, culturally, economically and socially, to the local communities.

“Even with an result, we would have taken the measures we did — i.e. the imposition of controls over the affected area and further sampling and testing.”

Mr Walsh advised about $295,000 had been spent on the response since the error was made.

The mistake had been picked up in an audit which began in late July, and involved its chief biosecurity officer reviewing all the documents, the testing process and interviewing those involved.

After this, the step was taken to send the samples to Australia for further testing.

“We received those results on August 19 and are releasing the information now.

“We would likely have been a little faster, but a number of key staff have been diverted by Covid resurgence-related work.”

He said there was confidence the parasite was present in Big Glory Bay, and ongoing testing had confirmed so.

The 2017, Niwa positive results which led to the farm depopulation were replicated and further confirmed using DNA sequencing at the National Centre for Biotechnology Information in the United States.

“The latest testing included a positive result from Big Glory Bay, which was confirmed both by sequencing at AHL and by the Australian animal health laboratory when we sent samples for confirmatory testing as a result of this issue.

“Again, we have no doubt about the presence of Bonamia ostreae in Big Glory Bay in 2017 and that it continues to be present there.”

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