R (on the application of MacDonald) v Secretary of State for Environment, Food and Rural Affairs [2019] EWHC 1783 (Admin)
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R (on the application of MacDonald) v Secretary of State for Environment, Food and Rural Affairs [2019] EWHC 1783 (Admin) concerned a challenge before the High Court, Queen’s Bench Division (Administrative Court) by Ms Helen Jane Macdonald to a decision to slaughter her alpaca, Geronimo, on the basis that he was infected with bovine tuberculosis (bTB) caused by Mycobacterium bovis, a contagious disease dangerous to other animals and humans. Mr Justice Murray dismissed the claim.
Ms Macdonald imported Geronimo from New Zealand in August 2017. Before leaving New Zealand he had twice tested negative for bTB using skin tests, the second on 31 July 2017. On 21 August 2017, as part of the Voluntary Camelid Testing Scheme, Geronimo underwent a serology test (an Enferplex 4-antigen test) which, following priming by a skin test 21 days earlier, returned a positive result. On 1 September 2017 the Secretary of State issued a movement restriction notice and on 5 September 2017 a Notice of Intended Slaughter (TN03 Notice). Ms Macdonald contended the result was likely a false positive given Geronimo’s history, quarantine, earlier negative tests and the farm’s high biosecurity measures. She requested a re-test. After correspondence, the Secretary of State agreed in September 2017 to a re-test but insisted on a protocol designed to maximise sensitivity: a skin test followed 10 to 30 days later by two serology tests (Ms Macdonald chose Enferplex 2-antigen and DPP VetTB). Geronimo tested negative on the skin test in November 2017 and negative on DPP VetTB in December 2017, but positive on Enferplex 2-antigen. On 21 December 2017 a second TN03 Notice was issued. Ms Macdonald challenged both that notice and the Secretary of State’s decision of 15 July 2018 (the Decision), in which the Minister confirmed the slaughter order after further representations.
Ms Macdonald’s principal objection was that repeated priming (Geronimo had undergone three injections of tuberculin for skin tests between September 2016 and November 2017) rendered the Enferplex tests unreliable and highly likely to produce false positives. She relied on evidence from her expert, Ms Karin Mueller, a veterinary consultant in camelid medicine, who stated that there was insufficient evidence to say categorically that priming does not cause artificially elevated antibody levels leading to false positives. Ms Macdonald also relied on the absence of clinical signs of disease, the lack of bTB on the New Zealand farm from which Geronimo came (evidenced by the farm owner, Ms Walker), negative results on other tests, and a warning from Mr Alastair Hayton of Synergy Farm Health (which developed the Enferplex test) that the results should be treated with caution given reasonable doubt from a clinical and epidemiological perspective. She requested a third test without priming and testing of a blood sample taken before the November 2017 priming, but the Secretary of State refused, considering further testing futile given two positive results.
The Secretary of State relied on section 32(1) of the Animal Health Act 1981, which empowers the Minister to cause to be slaughtered any animal affected or suspected of being affected with a prescribed disease such as bTB, as directed by the Tuberculosis (Non-bovine animals) Slaughter and Compensation (England) Order 2017. He defended the use of priming on the basis of scientific evidence set out in a paper entitled “The anamnestic boost effect of the skin test on antibody responses to M bovis in camelids – summary of evidence” (the Priming Paper), which recommended priming 10 to 30 days before a blood test to maximise sensitivity in detecting infected animals. A veterinary risk assessment completed in September 2017 by Dr Ricardo de la Rua-Domenech, APHA Veterinary Advisor, concluded that the likelihood of Geronimo being infected was high, given the very high specificity of the Enferplex 4-antigen test (approximately 99.66 per cent, meaning a false positive rate of about 0.34 per cent). The Secretary of State maintained that even if the prior probability of infection was very low, the positive predictive value of the test was high. He rejected arguments that priming caused false positives, noting that the Priming Paper acknowledged a potential concern but concluded that evidence did not suggest specificity was substantially affected by priming. His scientific adviser, Dr Shelley Rhodes, a senior research scientist at APHA, accepted that evidence on repeat priming was sparse but maintained the protocols were validated and evidence-based. The Secretary of State took into account that Geronimo showed no clinical signs but observed that bTB is a slow, progressive disease that can take years to manifest. He noted that although bTB prevalence in New Zealand is lower than in the United Kingdom, the country is not officially free from the disease and the farm from which Geronimo came was in a vector-risk area. He considered that maintaining confidence in the testing scheme and consistent enforcement across the camelid industry were relevant policy considerations.
Ms Macdonald’s grounds of challenge were that the Decision was irrational because the Secretary of State refused to recognise scientific and factual evidence showing the test results were unreliable, and that he failed to take into account relevant evidence, including the manufacturer’s warning, the absence of clinical signs, and the scientific uncertainty about priming. She contended the Secretary of State had closed his mind to increasing evidence that Geronimo was not infected and irrationally refused to permit further testing that would strengthen her case.
Mr Justice Murray held that the Secretary of State’s discretion under section 32(1) of the 1981 Act was broad and that the court must afford an enhanced margin of appreciation to a decision-maker in cases involving scientific, technical and predictive assessments. The court must be slow to conclude that an expert and experienced decision-maker had reached a perverse scientific conclusion and should not substitute its own view for that of a conscientious decision-maker acting in good faith with knowledge of the facts. The judge found that the conflict of evidence on the effect of priming did not establish that the Secretary of State’s assessment was irrational or perverse. Ms Mueller’s view that the evidence base was insufficient to say categorically that priming did not cause false positives fell far short of demonstrating that the science was flawed. The Secretary of State had considered the issue in detail, as evidenced by the correspondence and internal communications, and had given adequate reasons for his position. The Priming Paper showed that the issue had been examined; the conclusion that priming was essential where there was confirmed or strong suspicion of infection, and recommended for routine screening, was not so unreasonable that no rational decision-maker could have adopted it. The court noted that Mr Hayton’s recommendation of caution had been specifically addressed in correspondence. The judge rejected the submission that requiring priming before the re-test was perverse, finding that the protocol deliberately enhanced sensitivity at the expense of a slight reduction in specificity in order to reduce the risk of a false negative given the strong suspicion arising from the first positive test. That was a rational approach. The judge held that the Secretary of State’s refusal to order a third test was also a judgment for him to make; a negative result on an unprimed test would not resolve the matter given two previous positive results and the higher risk of a false negative without priming. The Secretary of State had taken into account all the matters Ms Macdonald raised, including the absence of clinical signs, the evidence from New Zealand, biosecurity measures and the manufacturer’s warning, and had given reasons for his conclusions. The judge accepted that broader policy considerations, such as maintaining confidence in the testing scheme, were not irrelevant. There was no evidence that the Secretary of State had closed his mind or acted perversely. In short, Ms Macdonald had not established any public law error entitling the court to intervene in the expert decision-maker’s exercise of discretion, and the claim was dismissed.
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