A restatement of the natural science evidence base relevant to the control of bovine tuberculosis in Great Britain.

Bovine tuberculosis (bTB) is a very important disease of cattle in Great Britain, where it has been increasing in incidence and geographical distribution. In addition to cattle, it infects other species of domestic and wild animals, in particular the European badger (Meles meles). Policy to control bTB is vigorously debated and contentious because of its implications for the livestock industry and because some policy options involve culling badgers, the most important wildlife reservoir. This paper describes a project to provide a succinct summary of the natural science evidence base relevant to the control of bTB, couched in terms that are as policy-neutral as possible. Each evidence statement is placed into one of four categories describing the nature of the underlying information. The evidence summary forms the appendix to this paper and an annotated bibliography is provided in the electronic supplementary material.

Introduction

Bovine tuberculosis (bTB) is a major disease of cattle that can also affect humans, and many other livestock and wild animal species [1,2]. Human infection has not been a major public health problem in developed countries since the introduction of milk pasteurization [3]. Advanced cases in cattle experience loss of condition, and this directly affects the economic value of the animal, but in most developed countries detection of infection leads to movement restrictions being placed on the herd, mandatory slaughter and considerable indirect losses for the farmer [4].

The incidence and geographical distribution of bTB in Great Britain has been increasing for the last two decades [5] (see also appendix; box 1), and the English and Welsh governments estimate that they have spent £0.5 billion in the last decade on testing, compensation and research with further costs being borne by the agricultural industry. All cattle herds are tested regularly for bTB, more frequently in areas of high incidence. Confirmation of infection triggers restrictions on cattle sale and movement, and the withdrawal of ‘Official Tuberculosis Free Status’ [4]. To reduce the risks of infection, farmers are encouraged to adopt preventive biosecurity measures. Much attention has also been paid to reducing the risk of transmission from wildlife reservoirs, of which the most important in the British Isles is the European badger, Meles meles [1,2]. There are vaccines available for bTB that provide some protection to badgers and cattle, variants on those used to protect against human tuberculosis [6]. EU law currently prohibits the vaccination of cattle as it can mask the detection of infection. The vaccination of badgers is the subject of intense current research [6,7], and vaccination has been under way in Wales since 2012 [8].

One strategy intended to reduce infection in wildlife reservoirs is culling. Badger culling was used routinely in the past [2], and its effectiveness was the subject of a major experiment, the Randomised Badger Culling Trial (RBCT), which ran from 1998 to 2006 [1,9]. Since then there has been no official badger culling, though the UK government has indicated its intention to allow culling in England, and badger culling at two pilot sites has been authorized for the summer of 2013 [10].

The prospect of badger culling has resulted in bTB policy becoming one of the most contentious areas of policy-making that involves science in the UK. The natural science evidence base is used by different sides to support different arguments, and exactly what constitutes natural science evidence has been called into question. The aim of the project described here is to provide a restatement of the relevant natural science evidence base written in a succinct manner comprehensible to non-expert readers and providing an entry into the technical literature. We have tried as far as possible to be policy-neutral, though realizing that this can never be absolute (the mere discussion of a strategy implicitly assumes it is a possible intervention). We hope that restating the scientific evidence will reveal the clear distinction between the science base, which is largely agreed, and the policy implications of that science base, which are hotly debated. This baseline summary also provides a natural starting point for a future review of evidence gaps.

Material and methods

The relevant literature on bTB in Great Britain was reviewed and a first draft evidence summary produced by a subset of the authors. At a workshop, most authors met to discuss the different evidence components and to assign to each a description of the nature of the evidence. Using existing systems such as GRADE [11], a tool for grading the quality of evidence used to support decisions in healthcare, we explored the restricted vocabulary used by the International Panel on Climate Change [12] to describe uncertainty associated with global environmental change, and ranking of evidence used by a study on bTB commissioned by the Welsh Government [13]. However, none precisely matched what we needed and instead we defined the following categories:

[Data] A strong evidence base involving experimental studies or field data collection on bTB with appropriate detailed statistical or other quantitative analysis.

[Exp_op] A consensus of expert opinion extrapolating results from other disease systems and well-established epidemiological principles.

[Supp_ev] Some supporting evidence exists but further work would substantially improve the evidence base.

[Projns] Projections based on available evidence for which substantial uncertainty exists that could affect outcomes.

These are explicitly not a ranking as, for example, some projections are firmly rooted in rich datasets, while some expert opinions are very much less so.

A revised evidence summary was produced and further debated electronically to produce a consensus draft. This was sent out to 25 scientists involved in bTB research, as well as to representatives from the farming industry, non-governmental organizations concerned with culling and Defra, the UK government department responsible for bTB policy. The document was revised in the light of much helpful feedback.

The project was funded by the Oxford Martin School (part of the University of Oxford), and though many groups were consulted, the project was conducted completely independently of any stakeholder.

Results

The summary of the natural science evidence base relevant to bTB policy-making in Great Britain is given in the appendix, with an annotated bibliography provided as the electronic supplementary material.

Discussion

We note several limitations of our project and how it might be extended.

First, the project considered only the natural science evidence base. There are very important social science issues involved with bTB policy-making that would also benefit from a formal evidence summary. For example, there are complex behavioural and behavioural economic aspects to the implementation of bTB control measures by the farming industry. Furthermore, the spectrum of possible interventions available to government is moulded by debate in civil society. The European Union's Common Agricultural Policy, and how each member state interprets it, shapes the economics of the livestock industry in Europe. The way agriculture is supported in England and Wales affects the structure of the countryside, including the wild animals that can harbour bTB. An entry into the social science literature on bTB is provided in the electronic supplementary material.

Second, the review concentrates on the evidence base from Great Britain. bTB is also a major problem in the Republic of Ireland, where badgers are a major reservoir. In Australia and New Zealand, successful efforts to control bTB have included targeting, respectively, introduced water buffalo (Bubalus bubalis) and brush-tailed possum (Trichosurus vulpecula), which act as reservoirs of infection. Differences in the regulatory and social structure of farming, the countryside, and the ecology of the different reservoirs all mean that lessons from other countries have to be taken with great caution, but the approach taken in this project might be usefully extended to consider more evidence from other countries. An entry into the literature on bTB control outside Great Britain is provided in the electronic supplementary material.

Finally, the review has largely concentrated on bTB epidemiology. We have not tried to summarize the evidence base relevant to the technical or operational logistics of culling or vaccination campaigns, nor the animal welfare consequences of different interventions.

We finish by stressing this is a consensus document written by the authors, and that we accept that a different group might have included or omitted different statements and might have categorized them in different ways. Policy-makers have to integrate evidence from the natural and social sciences, as well as to make political judgements about weighing the interests of different stakeholders. We hope the current summary will make it easier for evidence from the natural sciences to contribute to policy-making, and clarify where there is agreement and where dissent. We also hope that this restatement of the current evidence base will stimulate discussion about how to prioritize investment to address remaining uncertainties.

	average % change
	proactive culling area		areas surrounding cull
time period	central estimate (%)	95% confidence interval	central estimate (%)	95% confidence interval
during trial	−23	−12 to −33	+25	−1 to +56
after trial	−28	−15 to −39	−4	−26 to +24
entire period	−26	−19 to −32	+8	−14 to +35