The Bovine tuberculosis conference in London on 28th March 2017 was accompanied by media reporting that the Randomised Badger Culling Trial is no longer safe science on which to justify the mass culling of badgers. Ecologist and Badger Trust member Tom Langton reports on his year-long effort to investigate the deep science behind the justification for killing badgers.
Some people will insist that the badger cull is completely political. Yet in some senses, everything in society that is large-scale, expensive, complex and at the heart of a national industry, is bound to be political to some extent. Priorities, such as who gets the money and decisions on what success or failure may look like are political decisions. It is easy to ‘blame’ hidden agendas and dark forces, and they may to some extent exist. But quite often the answers are simpler and routed in the frailties and fallibility of humans – the human factor. And science with all its inner secrets and complexities is not immune from all that.
There is no shortage of science in badger culling. Whether it is the molecular biology of bTB strains, intricacies of bTB testing, badger, or cattle vaccination, the hands-on anatomy and pathology of disease investigation, population size estimation and trend analysis or modelling of hypothetical disease pathways. The list seems endless and a boggling arena for the non-biologist. Understanding the inter-relationships of these disciplines may require simultaneous insight into such areas of expertise and uncertainty. So, before we blame politicians too quickly, there is a need to look through the microscope at the science that is involved. After all, get two experts on any issue in front of you, any politician will say, and they are bound to disagree.
From 2013 onwards, the rallying cry of the ‘anti-badger cull’ movement was that badger culling could offer “no meaningful contribution to cattle bTB control in Britain”. This is a direct quote from the final (ISG 2007) report on the Randomised Badger Culling Trials (RBCT) that took place between 1998 and 2005. And that was also my understanding at the time, based on generalised reports of the published findings. The main conclusion from culling 70%+ of badgers over a six week period was that any reduced bTB transmission from badgers to cattle is offset by a ‘perturbation effect’, whereby increased movement of badgers due to culling, causes an increased transmission of bTB to cattle around a culling zone. By 2015, having attended a few protest rallies and with culling spreading to Dorset, it was clear that the animal conservation and welfare charities had completely failed to convince government that their policy was both wrong and not based on scientific advice. Checking the scientific detail became the last remaining option.
As an applied ecologist who has co-managed a large wildlife disease investigation, I had some relevant background for reviewing the RBCT. To start with, the science relating to badgers moving around more extensively during and after culling looked reasonably simple. It was a straightforward field study and well documented. The change in a number of other species such as foxes, expanding into the empty niches left by depleted badger populations was reasonably clear too- the science on that looked good and sound to me.
Then I moved on to the guts of the main 2007 Independent Scientific Group (ISG) report and the published statistical papers of 2005-07 and beyond to-2013. This was more tricky. It took me four months of evening and weekend reading to get fully into the near 300 page summary of the £50 million research project, and a further period with help from university professors and senior statisticians to get a grip on what exactly had been done. Along the way, checking with other biologists studying mammals, disease, or natural processes, I could find few who had studied it closely, as opposed to just parts of it and most were just generally aware of the various conclusions.
The RBCT had two types of culling (Reactive and Proactive), each planned in ten areas of around 100 square km in size. Reactive culling is where badgers are killed only on land within a few km of a new bTB herd breakdown and not widely over a large area as in proactive culling. But from 1998, RBCT badger culling had a faltering start, further hampered by the Foot and Mouth crisis in 2001 restricting access to farms. The result was a depleted data set due to these unforeseen circumstances. The ISG report nevertheless had come up with its hypothesis that badgers were giving bTB to cows rapidly by catching and passing it on via the ‘perturbation effect’. But for many, the speed of bTB transmissions involved looks unrealistically rapid for it to be a real phenomenon.
The sequence of events following disruption of badgers would need to be: increased transmission of TB amongst surviving badgers, newly infected badgers becoming infectious (a process taking months or longer), then infective badgers making contact with cattle somehow in a mechanism that is unknown, cows becoming exposed to bTB from the unknown pathway and establishing new bTB infection in vulnerable individuals, sufficiently to trigger responsiveness to the tuberculin test and detection at slaughter/post mortem culture/microscopy, breakdowns might need to wait six months on average (and up to a year for the next testing period) to be detected, during which time there was a 20-50% chance per cow of it being missed and possibly picked up in a further year’s time or longer.
Reviewing the literature on BTB and badgers, I found a group of six academics including Professor Simon More from the Centre for Veterinary Epidemiology and Risk Analysis in Dublin who had studied the ISG and published an immediate critique of several aspects. In addition, the record showed Sir David King (Chief Scientist at the time) had set up his own expert group that effectively dismissed the strength of the statistics concerning reactive badger culling and the bTB spread via the perturbation effect. More recently, the Chief Veterinary Officer for Wales has drawn the same conclusions as those before her. So now we have three separate expert appraisals saying independently that reactive culling and perturbation effects are not safe science. All in all, the suggested increase in bTB transmission would have been likely to take years if indeed it was real at all. The cold fact is that the duration of the reactive cu