The science of bovine TB control is like a cherry orchard: it offers an abundance of evidence that you can pick through, selecting fragments that seem, on their own, to support almost any position on TB management. There is evidence that badgers transmit TB to cattle, and also evidence that most cattle herds catch TB from one another, not from badgers. There is evidence that killing badgers reduces cattle TB, and also evidence that it increases cattle TB. To scientists, this seemingly conflicting evidence forms a coherent picture. But in the wider world it feeds a controversy which rages on social media and spills out into the countryside, where the government last year spent over £4 million on police efforts to keep the peace between those killing badgers and those protesting against it. Sadly, controversy helps neither the thousands of farm businesses affected by TB each year, nor the thousands of badgers slaughtered in hopes of controlling the disease.
In this context, a new review of TB strategy, conducted by a team chaired by Professor Sir Charles Godfray, provides a welcome reminder to all sides of just where the weight of evidence lies. The report states clearly that TB control efforts have focused too heavily on managing badgers, when most transmission occurs from cattle to cattle. The report makes some bold proposals about how to prevent such transmission, including using cattle tests which detect a higher proportion of infected animals (at a cost of also generating more false positives), improving the tracing of traded cattle, and punishing farmers for poor biosecurity through substantially reduced compensation.
Importantly, the review calls out Defra ministers on their repeated statements that “no one wants to be culling badgers forever” and gives the first proper consideration to how government might sooner or later exit from its culling strategy. It identifies badger vaccination as a potential alternative, and refers repeatedly to the “great importance” of obtaining evidence on how vaccinating badgers might reduce TB in cattle. Godfray’s team therefore propose a trial in which culling areas transition, after their four-year culling licences expire, to either annual vaccination or periodic repeat culling. This proposal is positive for two reasons. First, it implies an end to “supplementary culling” after four-year culling licences expire, a practice which is not supported by scientific evidence. Second, it provides a concrete opportunity to explore alternatives to culling on a meaningful scale.
However, vaccination is likely to reach its full potential more slowly in former cull zones than in areas which have not previously been culled. Culling weeds out the animals that are easily captured and so, after four years of culling, it will be more difficult to capture badgers for vaccination. Moreover, while vaccination works by protecting animals which have not yet been infected, culling increases infection prevalence in badgers and, correspondingly, reduces the number of animals that can be protected by vaccination. Hence, a trial conducted entirely in former cull zones is likely to under-estimate the true potential of badger vaccination as a TB control tool. Given the desirability of a nonlethal approach to TB control, it would be well worth including a third “arm” to the trial, where vaccination is implemented from the start, without any culling. This approach would show, for example, whether culling for four years and then vaccinating for five years would be more or less effective than just vaccinating for nine years. Because vaccination is substantially cheaper than culling, recruiting new areas to vaccination rather than culling would save the government money, and might be more acceptable to some landowners, as well as to the general public.
The report comes at a time when Defra is under fire for misrepresenting the evidence surrounding the effectiveness of badger culling. Godfray’s team was specifically asked not to evaluate whether the ongoing culls are reducing cattle TB, and a recent report from the Animal and Plant Health Agency (APHA) stated explicitly that the data it presented “cannot demonstrate whether the badger control policy is effective in reducing bovine TB in cattle”. Nevertheless, Defra published the APHA report alongside quotes from Ministers which claimed that the culls were “delivering results”. Clearly, a worrying gap still remains between scientists’ and politicians’ interpretations of scientific evidence. Hopefully Godfray’s report, conducted by scientists working independently of Defra, free to speak publicly about their conclusions (unlike APHA scientists), may go a way to bridging that gap.
The report also discusses the potential for TB control to be overseen by a new body, separate from APHA and Natural England. This proposal is rather worrying, because the badger is a protected species, and decisions about its management need to be taken by an organisation tasked with conserving wildlife, rather than one which views it simply as a pest. The suggestion that government might consult less often on TB control measures is also cause for concern.
Overall the Godfray team’s report is a useful step forwards. The government has promised a response in summer 2019: whether and how it takes up Godfray’s recommendations is likely to determine whether it succeeds in managing a major livestock health problem in a way which is both effective and sustainable.
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