Defra stands firm on its TB testing policy

DEFRA believes it has no lessons to learn from the Hallmark Boxster case.

The Yorkshire Post asked the Animal Health and Veterinary Laboratories Agency to answer some questions which farmer Ken Jackson and family felt were left unanswered after they spent 18 months proving that a positive TB test on the bull was wrong.

Q: In view of the Hallmark Boxster case, will there be any attempt to check the level of misdiagnosis arising from the blood test for bovine TB?

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A: No. We have complete confidence in our bovine TB testing regime. All research and field evidence shows that the gamma interferon test has a very high degree of accuracy and is effective at disclosing infected animals missed by the skin test.

Q: Does Defra now accept that the first blood test on Boxster gave a false positive and what steps can be taken to avoid a repeat of that mistake?

A: It’s difficult to say exactly what happened in this case. Most cattle would give the same test results consistently over time. However, there are a number of factors that can lead to different test results at different times including: no diagnostic test being 100 per cent accurate; the time elapsed between tests; and the complex nature of animals’ immune responses to the TB bacteria, which are not static but evolve over time.

Q: In view of the fact that misdiagnosis is clearly possible, why cannot farmers be allowed to pay for their own tests when there is reason to doubt a result from Animal Health and/or the animal is especially valuable?

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A: The interferon-gamma test has a very high degree of accuracy and about 97 per cent of cattle that test positive will be true positives.

If blood samples have not been collected in full accordance with field guidance notes, a retest will only be agreed if the failure to follow field instructions would be likely to affect the validity of the test result, based on our expert scientific advice.

When cattle test positive it is our duty to remove the animals. Given the seriousness of the bovine TB problem it is important that controls are applied consistently and with rigour.

Q: In view of the fact the blood test was considered an essential decider in this case, why can cattle be sold out of Wales on the basis of a single skin test? Is this the case in English hotspots too?

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A: In high bovine TB incidence areas in England and Wales, cattle from officially TB-free herds must test negative before moving to a low incidence area.

The gamma interferon test is used alongside the skin test in specific circumstances. In this particular case, the herd was located in a low TB incidence area and bovine TB had been confirmed in an animal from it. In such herds, the gamma interferon test is used to ensure as far as possible that no cases of infection are missed, and so reduce the risk of bovine TB getting a firm foothold in new parts of the country.

Q: Is it correct that farmers could have the option of vaccinating their cattle against bovine TB if the government was prepared to give up exports of live cattle to the rest of the EU?

A: Not at the moment because vaccinating cattle against bovine TB is banned under EU and UK law and in any case, there is as yet no licensed cattle vaccine available against bovine TB.

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In the longer term, Defra’s funding of research and development work will support the possibility of the licensing of a vaccine for use across Europe. But before it can be deployed in the field, EU law will need to be changed.

Cattle vaccination has the potential to make a significant contribution to the control and eventual eradication of bovine TB. However, vaccination cannot guarantee that all cattle will be fully protected against bTB and is therefore unlikely ever to be suitable for use as a sole eradication strategy.

Cattle vaccines are currently prohibited under EU legislation as the lead candidates are based on BCG, which can interfere with the tuberculin skin test. Some vaccinated cattle could therefore react positively to tuberculin as if infected by bTB, and herds could not be declared Officially TB Free.

Daughter wouldn’t give up

BOXY the bull’s owner’s daughter, Kate McNeil, got deeply involved in the research which forced Defra to give the bull a second set of TB tests, leading to an all-clear.

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She said the Defra responses were “a classic example of Defra appearing to answer the question while actually avoiding the point”.

She is sceptical of the department’s claim of 97 per cent accuracy in bovine TB testing – and the campaign Rethink BTB says it is “seriously misleading”. But in view of Defra insisting the gamma interferon (blood) test is particularly precise, Kate asks: “Shouldn’t this be used with the skin test in high-incidence areas across England and Wales?”

The Defra answer to Question Two, about how Boxster got a false positive in the first place, left Kate puzzled over its meaning.

“Boxster has passed not only a blood test but three skin tests,” she commented. “Are they suggesting his immune response is hiding a truly infected animal?”

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She was particularly interested in the response to our question about why farmers could not be allowed to pay for a second opinion. All her father ever wanted was a repeat of the flawed blood test on Boxster. But it cost him £120,000 in legal fees to get it.

Defra returns to stressing the accuracy of the test, implying it was just a fluke that it was proved wrong in the one case it has been repeated on the same animal.

A court declared the first test invalid because two blood samples were mixed. But Defra does not even concede, as the judge advised, that farmers are entitled to expect best possible practice.

Kate commented: ““They say a retest will only be agreed if failure to follow field instructions would be likely to affect the validity of the test result, based on their expert scientific advice.

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“In the Boxster case, three Defra experts all stated, in several report papers, that his blood result would not have been affected by their handling of the samples. Our expert contradicted their opinions and has now been proved correct. But they appear to be saying farmers will still not have a legal challenge if they decide they are right, like they did in our case.”

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