One such was the Somerset based Higher Burrow Organic Farmering Partnership, where over 430 animals were tested late last year. Of those, 14 had a positive skin test result. But in accordance with Defra policy of using the newly approved blood test as a herd test in such cases, the cattle underwent parallel GammaIFN testing. The results showed that 86 were positive, while eight results were indeterminate.
Concerned farmers in several herds so affected, requested the primary skin test as backup, as the disparity between the blood test results and intradermal skin test was so great. Defra said no and ordered slaughter. So for months several farms have been snarled up with hundreds of cattle awaiting the results of last week's request to the High Court for a Judicial Review into that apparent disparity.
Newspaper reports which covered the story quote:
Hugh Mercer QC, for High Burrow, who said the two sets of tests showed "a massive disparity". Slaughter without re-testing would be "unlawful, irrational and disproportionate".The case has been adjourned once already, so that reams of "evidence" could be cogitated and digested, but in one fell swoop, last week, sitting judge, Mr. Justice Mittings dismissed the request saying "the policy is lawful".
He said: "The policy is lawful. The outcome – unhappy and potentially disastrous though it may be – flows from it."So what of this policy? Where did it have its roots and how was it trialled in the UK?
Defra will say that the blood test was "developed in Australia in the 1980's", but what they are not so keen to explore is that Australia achieved Tb free status ahead of its licensing, using the intradermal skin test - and a clearance of feral cattle and water buffalo, acting as a maintenance reservoir of tuberculosis. Australia also has a hugely different environment from the UK, with many less contaminants to affect the test results.
But in 2006, Defra began a pilot study known as SB4021. They snuck under the radar of 24 farms in 3/4 year testing areas, using bloods from other testing regimes, and tested for bovine Tb. In these areas they would not have expected to find anything at all, but they did. In fact seven percent of samples proved positive. As this test was not a recognised diagnostic test at the time, they could not confirm their findings with slaughter. Specificity and sensitivety of any diagnostic test are interlinked values, but the authors of the report had a much better idea.
The pilot study indicated vastly differing results for length of time in transit of bloods, possible co contamination with recent skin tests, and several other known contaminants including skin granulomas, the precence of antibodies or vaccinates to Johnnes disease (M. avium paratuberculosis) and certain mosses - as well as M. kansassii.
No post mortems were carried out to confirm their results, but Defra presented this ragbag of selectively culled information to the the Standing Veterinary Committee of the EU for approval as a secondary diagnostic test for bTb.
As a secondary test, a gamma negative animal still requires a primary intradermal skin test to regain its status, yet in the bizarre world inhabited by Defra, a postive result means the chop. And this is at the root of what the farmers challenging official Defra policy last week in the High Court were asking for. Parity for both animals, particularly as the bloods had shown such, err - disparity, of results.
Mr. Justice Mittings described Defra's decision to slaughter the animals as
"not only lawful but mandatory".Mandatory under EU law, based on a small "pilot study" which excluded or ignored results which it did not expect? Rock solid science then.
The blood test was sold to an unsuspecting industry as "flexible in interpretation", but we see little sign of that, with a fixed cut off point now applied and no allowances made for other known contaminants. It was also described as picking up "very early cases". But that too turns out to be somewhat of an exaggeration. The difference between the latency of the intradermal skin test and gammaIFN is about two weeks, with the skin test averaging 42 days and gamma 28 in experimentally infected animals.
But a delicious twist has given one farmer in the queue for a re-test using the primary intradermal skin test, exactly what he wanted. While the cattle at Higher Burrow await their fate, 31 cattle at Tom Maidment's farm in Wiltshire have been retested. 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 AHO who, very obligingly, when the 60 day re-test was due, ordered Mr. Maidment to - err, retest his cattle.
Only too keen to oblige, Mr. Maidment's cattle were skin tested and the results interpreted under severe interpretation. All were clear. All passed. No lumps. Anywhere. Not one.
Which makes Mr. Justice Mittings' statement:
there was no evidence that those blood tests might, if retaken, prove negative...rather timely. (Or had the learned judge not realised that the last thing the farmers were asking for was another blood test, but the primary skin test?)
And which is probably why, when assessing the relative accuracy of the gammaIFN blood test, Defra are not so keen to reveal that while about half (48 - 51 percent)skin test reactors slaughtered show VL (visible lesions) from the cattle's exposure to M. bovis, at post mortem, 81.4 percent of cattle slaughtered as gamma reactors show no sign of disease whatsoever.