A study says tuberculosis in cattle could be most effectively controlled by the mass culling of the UK herd. But what is the most practical way to combat the disease? With your help, Karl Mathiesen investigates.
Let us know your thoughts. Post in the comments below, email karl.mathiesen.freelance@guardian.co.uk or tweet @karlmathiesen
2.43pm BST
Mark Downs, chief executive of the Society of Biology, said past outbreaks in cattle, such as foot and mouth disease and bluetongue, should inform the response to bTB and make the development of an appropriate and legal vaccine a priority.
The vaccine BCG (Mycobacterium bovis Bacille Calmette-Guérin) has been shown to be somewhat effective in blocking the disease in individual animals, but it is unclear how it would behave in herds. Yesterday's study modelled the effect of vaccination and showed that it could be effective in stopping bTB spreading. The major issue with the vaccine is that some vaccinated cattle will show a false positive under the current testing regime. This has lead the EU to outlaw the vaccination.
1.24pm BST
Defra's chief scientist Ian Boyd has responded to the study in a blog. He says the assertion that a mass cattle cull would be an effective way to stop TB is a bit of a no brainer.
On the face of it, this is not a very profound outcome especially when one considers where the uncertainties might lie within the model. The model itself is provided with most information about cattle-cattle transmission of bTB and, while few would doubt that this is the most important route of infection in cattle, it is not a surprise that if one was to intervene very hard to eliminate the disease by eliminating cattle then the problem (i.e. the control of TB in cattle) converges on a solution. Clearly, if the end point is zero cattle, which could be an outcome of such an approach, then the problem has been solved. It did not need a sophisticated model to tell us this.
A key issue is whether badgers are able to sustain disease without the presence of cattle. This paper suggests not but I am not so sure we have evidence strong enough to support such an inference from a study that made so little effort to model the badger component of the disease cycle.
Does this mean that badger-cattle infection is unimportant or is it just left relatively unseen in all the noise of uncertain data, model simplification and (possible) selection bias by those carrying out the study? There are other data that suggest another story, such as the genetics of bTB that show an important epidemiological link between badgers and cattle.
"Rather, it is a problem associated with the way in which the costs of different management interventions are divided between different stakeholders. We need to understand how these interventions might be implemented in ways that are accepted and this is a social science problem."
The interventions suggested here would affect the lives, careers and livelihoods of many thousands of people and acting on them would require a much higher level of certainty than are present in the paper.
12.50pm BST
Vaccination may only work on badgers (and cows) without TB, but if vaccination coverage is good enough (and the vaccine effective enough) then transmission of the condition falls to very low levels, few new carriers are created and as the old carriers die the illness dies with them. It's called herd immunity.
Quite simply firmly clamp down on cattle movements and vaccinate both badgers & cattle as it becomes available. A reduction of agricultural intensity would undoubtedly help to reduce stress and overcrowding, but its harder to enforce.
This is not a complex issue.
12.45pm BST
TB spreads between cattle in various ways. The largest factor is the movement of infected animals between herds and farms. Testing sometime delivers a "false negative", missing animals that are in fact, carrying the bacterium. Environmental effects, including badger, cause only 15% of new infections.
12.35pm BST
Study author Matt Keeling has published a blog on the Conversation that builds on the media reports yesterday and the press release accompanying the study.
Keeling's study found that vaccinating cattle could stop the spread of TB. A significant and novel finding. But a vaccine remains unlicensed in the EU because vaccinated cattle cannot be differentiated from infected cattle under current testing regimes.
12.30pm BST
Matthew Kelly has written a lovely account for the Guardian on the long and troubled relationship between British cattle farmers and 'brocks' (badgers). We've been here before.
12.16pm BST
The Science Media Centre have done a round up of reaction to the study. Most agreed the study was a useful, although simplified tool, for understanding the cause of TB spread.
Rosie Woodroffe from the Zoological Society of London (ZSL), said:
The model suggests that [badgers and contaminated farmland] is responsible for just 15% of herd infections. While this finding needs to be interpreted with caution, it does echo the findings of a model by Donnelly & Nouvellet which suggested that 6% (and a maximum of 25%) of new herd incidents in cattle were caused by direct transmission from badgers to cattle."
Although their work is compelling, the authors job is not complete. Policymakers often speak of their use of a package of measures and every tool in the box in controlling bTB, particularly with respect to controversial policies to cull badgers. Brooks-Pollock et al. now have the perfect opportunity to use their model to test policymakers expectations of their various packages and tool-boxes and to gauge their overall cost-effectiveness. UK governments and the farming industry badly need such guidance to frame and implement their overall strategy and to manage expectations among their diverse stakeholders."
Based on our current understanding of the disease cycle, the more severe control measures suggested by the paper would probably result in a rapid decline in the cattle industry in areas where TB occurs. However, the study reinforces the basis of the current TB control strategy which is designed to cope with complex and diverse routes of infection.
The sophisticated model and conclusions described in this paper give further support to the view that culling badgers is not an effective strategy for controlling bovine TB. Instead the emphasis should be on stopping cattle-to-cattle transmission. It is to be hoped that Defra takes on board this latest piece of scientific evidence when they formulate their policy for the future.
12.00pm BST
While the prospect of a mass cattle cull grabbed the headlines, there were a number of key points in this study that could genuinely inform the government's approach to this problem.
Testing with 70-90% success means herd management must continue to be intensified
Using such a test necessitates the use of multiple follow-up tests following a positive test on a herd to increase the chance of detecting all infected cattle. Movement restrictions are placed on herds until they pass one or two follow-up tests at approximately 60-day intervals, and once movement restrictions are lifted two further tests are required after 6 and 12 months. In 20102012 there was a marked expansion and consolidation of testing protocols in England, culminating in 2013 with the division of the country into annual testing counties in the south and west and four yearly testing counties in the east and north.
84% of newly infected farms and, crucially, that there was a heavy bias towards as few as 10% of farms, characterized by selling many animals, as the source of nearly all secondary cases. Similarly, a small minority of farms seemed to be responsible for spread through the environment. Thus, a key finding of the study is that a small proportion of farms probably function as superspreaders of bTB infection.
An across-the-board 50% reduction of all sources of environmental transmission, simulating successful culling or vaccination of badgers, was shown by the model to have little impact on any measures of cattle disease, and failed to prevent ongoing growth of the epidemic.
11.47am BST
Bovine TB is contracted by breathing in the M. bovis bacteria. Apart from respiratory transmission, it is also thought to be caught from bodily fluids (saliva, urine, droppings, pus from abscesses, etc.). This means animal density is a major factor in the spread of the disease. Badgers can also carry the disease.
Because of the potential for the disease to transfer to humans, TB is a major economic problem for farmers who were forced to slaughter 26,000 infected animals in 2013. Incidences in the southwest UK have been rising for 25 years.
The spread of bovine TB in the UK. Source: @nature http://t.co/ivYewzv8ce pic.twitter.com/pcC8CqqpKO
11.09am BST
The authors of the report have distanced themselves from advocating a mass cattle cull. In yesterday's press conference, professor Matt Keeling told reporters:
"We're being very categorical. We don't propose whole herd culling. We've looked at it as this utter extreme that says if you went wall out to control it, what could you possibly do? That's the most you'd ever get in terms of control and it still doesn't go down to nothing quickly."
"The model reveals the complex nature of bovine TB epidemiology and hence the difficulties faced when trying to control infection. We would like to stress that we have never viewed this work as advocating any one policy, and we do not criticise current control measures. Whole herd culling was investigated as one extreme but was never put forward as a viable policy option. Throughout we have stressed that any decision requires input from multiple sectors with scientific prediction only forming one element.
10.42am BST
The Guardian's Damian Carrington wrote last night:
The work is the first national-scale model of how the disease spreads and also found that more rigorous cattle testing and cattle vaccination would significantly curb the disease. But it concluded that the impact of the governments favoured option of a widespread badger cull would fail to prevent the epidemic growing.
The one-off cull of all cattle in infected herds which is considered in the new paper would see over 250,000 animals slaughtered, about 20 times the current annual rate, though far fewer than the 6.2 million animals killed in the 2001 foot and mouth epidemic. Prof Matt Keeling, an epidemiologist at the University of Warwick and one of the research team, acknowledged the measure would be draconian and unpopular but said that, because the cattle cull would cut TB infections, far fewer cattle would be slaughtered in following years. This might be an acceptable cost if one is prepared to take a sufficiently long term view, the team write in the paper.
10.40am BST
The mass slaughter of the UK cattle herd would be the most effective control measure for bovine TB, according to a research published yesterday.
The study in the journal Nature, says the UK's current policy of culling badgers (which carry the disease) will only marginally affect the spread of infection. Instead, the authors suggested slaughtering 250,000 cattle would be the best way to combat tuberculosis, which costs the UK taxpayer more than £100m every year.
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