14 cattle revealed as positive reactors when skin tested but 86 from the same herd when using the blood test! Print this pagePrint this page

An organic dairy farm partnership in Somerset, Higher Burrow Organic Farming, with a herd of over 400 cattle suffered catastrophic effects when the blood test was used on their herd in 2007. The partnership lost valuable organic animals, and thousands of pounds, exacerbated by the fact that the compensation received was based on table valuations and not individual values (the system changed in 2006). They also ended up having to pay significant legal costs.

In September 2007 the farm underwent a routine four-year skin test. One animal tested positive for bovine TB. It was an animal that had been bought in during the previous year. In late November 2007 the herd was tested again. The skin test revealed 14 of the 486 cows as positive reactors. However, DEFRA also used the new gamma interferon (gIFN) blood test, and this revealed a total of 86 positive reactors – 72 more than the skin test!

There were serious concerns that the two tests gave results too inconsistent to be credible and a re-test was sought. However, DEFRA refused this request and insisted that all reactors had to be slaughtered regardless of the test used unless the VLA laboratory, which had analysed the results, cast doubt on the validity of the blood test results. This was not believed to be the case and slaughter of all the reactors was again demanded. The farming partnership opted to apply for a judicial review, particularly as it became clear that other farms were experiencing similar results when the blood test was used.

Defra sought to destroy the animals in January 2008, but agreed not to cull them pending a judicial review, which was due to be heard on February 12. The basis of the challenge was that a re-testing should take place when the test results are statistically surprising. The challenge was made in the context of the disastrous consequences for the individual farmer of being forced into the slaughter of all reactors.

Tim Russ, a partner and agricultural law expert at Clarke Willmott, said: "Tests for bovine TB were conducted using the skin test and the gamma interferon (gIFN) test. Whilst the skin test showed just two or three cases of TB, the gIFN test showed 100. This suggests that there is something seriously wrong with one or both of these tests.” He went on to say "The slaughter of these 100 animals would cost the Higher Burrow Organic Farming Partnership more than £100,000 and we simply wish Defra to re-test before these animals are removed unnecessarily." Clarke Willmott was also acting on behalf of two more farmers, one in Dorset and one in Wiltshire, who were in a similar position. The lawyers said it was ‘statistically impossible’ for the tests to be accurate.

At the time even shadow agriculture minister, Jim Paice, was reported to have said that although he still had confidence in the blood test ‘questions had to be asked’ when such disparities arose. Media reports claim he said; “It is outrageous that Defra is refusing to do a re-test. That is only sensible.”

At the hearing Hugh Mercer QC, for the High Burrow Partnership, said the two sets of tests showed ‘a massive disparity’ and slaughter without re-testing would be ‘unlawful, irrational and disproportionate’.

The case was adjourned once so that reams of ‘evidence’ could be cogitated and digested, but then in April 2008 the judge, Mr. Justice Mittings, dismissed the case saying that DEFRA’s policy was not irrational, unlawful or disproportionate. ‘The outcome – unhappy and potentially disastrous though it may be – flows from it.’ The disastrous consequences to the farmers were completely ignored. Permission to appeal was refused and DEFRA was awarded its costs - £29,144.50.

The judge declined to discuss the scientific reliability of the two tests. Instead he ruled that DEFRA's decision to slaughter the animals was ‘not only lawful but mandatory’. His judgment was based solely on the law and he ruled that, because the blood test had been approved by the EU, it was therefore lawful for DEFRA to rely on it. So, even though the EU had regarded the gamma interferon blood test as only an ancillary test, not to be relied on for a definitive diagnosis, the cattle had to be slaughtered and tens of thousands more cattle across Britain were therefore doomed. In view of this decision, none of the other farmers considered it worth continuing with legal action as, based on Justice Mitting’s ruling, they were not likely to win.

The ‘Note of the Judgment’ includes some interesting information. The judge noted that one of the expert witnesses, Mr Hayton, accepted that there was no perfect test for bovine TB, whether in a living or dead animal. He identified the probability of the Higher Burrow results occurring as one in fourteen thousand! This was said to suggest that something must have gone wrong in the testing –this was not the only farm which had surprising results using the blood test.

The Claimant used a specialist in epidemiology as one of their expert witnesses. He put forward five hypotheses, to explain the statistically surprising results at Higher Burrow:

1. Large number of animals at early stage of infection (explosive outbreak). 2. False positives due to contamination or reaction with other mycobacterial species (eg avian TB – widespread in the UK!). 3. Possible reaction to unknown antigens (eg in unusual feedstuff). 4. Sample contamination. 5. Errors in laboratory testing.

The last three were ruled out in the Higher Burrow case. DEFRA’s expert witness believed it was 1 and the Claimants’ witness believed it was 2. The judge noted that judicial review proceedings were not an appropriate forum for deciding scientific questions of this kind.

Background to the infamous blood test

The gamma interferon blood test evaluates the same immune response that the skin test does but is conducted in the laboratory using blood samples. Back in 2006 DEFRA began a pilot study involving the new gamma interferon blood test. Apparently they secretly selected 24 farms in three to four year testing areas, using bloods from other testing regimes, and tested for bovine TB. Apparently in the areas selected they would not have expected to find any evidence of bTB in the cattle. However, they did – around 7% of samples proved positive. As the blood test was not a recognised diagnostic test at that time, they could not confirm their findings with slaughter. The pilot study highlighted problems associated with issues such as the differing results for length of time in transit of the blood samples, possible co-contamination with recent skin tests, and several other known contaminants, including skin granulomas, the presence of antibodies or vaccinates to Johnnes disease (M. avium paratuberculosis) and other diseases. So, despite the fact that no post mortems were carried out to confirm their results, DEFRA presented the results to the Standing Veterinary Committee of the EU for approval as a secondary diagnostic test for bTB and approval was obtained.

As the blood test is an ancillary test, one would assume that it would need to be backed up with a positive skin test. However, this is not the case. If an animal fails the blood test it must be slaughtered.

The blood test was sold to an unsuspecting industry as ‘flexible in interpretation’. This has not been the case and no allowances are made for other known contaminants. It was also described as picking up ‘very early cases’. This too is somewhat of an exaggeration. The difference between the latency of the intra-dermal skin test and gamma IFN is about two weeks, with the skin test averaging 42 days and gamma 28 in experimentally infected animals, which is probably why, when assessing the relative accuracy of the gamma interferon blood test, DEFRA are not so keen to reveal that while about half (48 – 51%) skin test reactors slaughtered show visible lesions from the cattle's exposure to M. bovis, at post mortem, 81.4% of cattle slaughtered as gamma reactors show no sign of disease whatsoever!

The Bovine TB Blog (http://bovinetb.blogspot.com) revealed that another farmer, who had been waiting to bring his own case to court, was Tom Maidment of Wiltshire. Thirty-one of his cows were condemned by DEFRA after blood testing had declared them to be positive reactors. He pleaded in vain with London to have them skin-tested. Mr. Maidment and his vets had engaged in long correspondence with DEFRA (London) and DEFRA (Veterinary Laboratories Agency) but not the clerks at the local Animal Health office who, very obligingly, when the 60 day re-test was due, ordered Mr. Maidment to - retest his cattle using the skin test! Only too keen to oblige, Mr. Maidment's cattle were skin tested and the results interpreted under severe interpretation. All were clear! DEFRA's response was that the cows must all, nevertheless, be destroyed. ‘’Who gives a fig for science when someone else is footing the bill - and the courts are there to support you?’ Sadly the courts ruled his cattle too had to be slaughtered, despite passing the skin test and he had to pay £10,000 in court fees. No evidence of TB was found. This was yet another tragedy for the poor farmer and what a waste of public money.

Official figures reveal that over 80% of all cattle destroyed after being shown as positive by the blood test proved, at post mortem, to show no signs of bovine TB. The reliability of the blood test remains highly suspect. It was originally designed to be just a quick surveillance test, to be confirmed by the skin test. DEFRA apparently even admitted on its website that the blood test is cruder and less ‘specific’ than the skin test, in that it picks up the presence of diseases other than bovine TB, most not harmful to cattle at all.

Information sources:

Note of Judgment, high court appeal Higher Organic Farming Partnership (claimant) and the Secretary of State for the Department of the Environment, Food and Rural Affairs












Free CMS by ViArt Ltd