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Britain's attempt to eradicate cattle TB
The British have been trying to 'eradicate' (or more correctly to 'eliminate') bovine TB since 1935. A compulsory test and cull programme began in the 1950s, and by 1960 all cattle in the country had been thus screened. The disease was not eliminated, but the percentage of herds found infected had been reduced to 2% per annum. Continuing the cattle testing and cull programme reduced this to well below 1% in most of the country, but only to about 1.5% in the south-west.
In 1973 the UK Ministry of Agriculture concluded that cattle TB had not been eliminated because wild badgers were providing a reservoir of infection. Since the policy in Britain was (and still is) to 'eradicate' rather than control animal diseases, the government embarked on a badger removal policy that was to extend on-and-off to the present time. At first farmers on affected farms were allowed to kill badgers by shooting. Concern about the welfare implications of this method led to the government taking over control operations. Badgers around infected farms were sampled, and infected social groups (and neighbouring ones) were gassed with hydrogen cyanide. Note that the focus was on removal of infected groups, so 'cull' was the appropriate term to use.
At first these measures appeared to be successful in further reducing the cattle infection rate, but from 1980 the percentage of infected herds started to increase again, especially in the south-west. Various badger culling strategies were tried, but none halted the increase. By the mid 1990s something clearly had to be done - but what?
The use (and disuse) of science
A scientific review chaired by Professor Krebs was set up to examine the evidence. That review concluded that there was evidence for an association between TB in badgers and cattle, and recommended a properly conducted randomized trial (as per medical trials) to assess the impact of three 'treatments' upon the number of disease outbreaks. Those treatments were:
All three 'treatments' included regular cattle testing, and culling of infected cattle.
This trial faced many problems in its execution, especially because of an unrelated outbreak of Foot and Mouth Disease in 2001 (the latest such, following its 'eradication' some years previous). As a result the routine cattle test and cull bovine TB programme fell apart. This led to a marked increase in bovine TB because of cow to cow transmission. It also led to an increase in badger infection rate apparently because of cow to badger transmission. Despite these problems, the trial was eventually completed.
It showed that:
Removing most badgers over small areas in response to outbreaks (reactive culling) was counter-productive because infected badgers dispersed over a larger area.Removing most badgers over a large area did reduce cattle infection rates by 20-50%, but was probably not cost-effective, even without taking account of the value of the wildlife resource.In 2007 it was concluded that badger culling could make no meaningful contribution to cattle TB control in Britain. The government of the time provided increased funding to a research programme to develop a vaccination approach (for cattle and badgers).
In 2009 the recently elected government abandoned that policy and decided to reintroduce badger culls. These are planned to start in 2012, this time by farmers 'free-shooting' badgers when emerging from their burrows in the evening. Cost issues were settled (supposedly) by farmers and landowners having to pay for the cull themselves.
Eradication or control
Before assessing the wisdom of the new approach, we first need to decide whether we are trying to 'eradicate' (permanently and completely eliminate) cattle TB in Britain, or whether we want a cost-effective control method. Recall that, since Britain 'eradicated' Foot and Mouth Disease (FMD) it has repeatedly faced enormously expensive measures to keep the country 'FMD-free'. The same would happen with bovine TB, even if disease elimination could be achieved in Britain. Eradication is also politically and practically problematic since cattle TB has several wild maintenance hosts in Britain. Eradicating cattle TB would entail completely wiping-out UK badger & deer populations - perhaps the ultimate misuse of the word culling (which actually means selectively killing weak or diseased individuals).
Farmers, veterinarians and politicians naturally would argue that killing all badgers is unthinkable, and that they only want to reduce the number of badgers. Nevertheless the trials clearly indicate that the only cull which would have any effect is a reduction of badgers by 70 to 80%. This is frighteningly reminiscent of the (failed) attempt to eradicate tsetse flies from southern Africa by game elimination. Between the 1920's and 1960, 1.3 million game animals were killed, including many species (such as rhino) which are now endangered. This is now regarded as an appalling waste of resources - as would be the wide scale elimination of Britain's largest remaining wild predator. The British badger population has high value in international conservation of the species, simply because it is the largest, most stable population in Europe not adversely affected by hunting.
The way forward
So where does that leave us? If both badgers and cattle have value, it takes us firmly to the vaccination option for both cattle and badgers. We already have a moderately effective vaccine for cattle, but governments will not use it because its use will interfere with the drive to 'eradicate'. But if our aim is cost-effective control of bovine tuberculosis, we should use the vaccine now. This is supported by the Small Farms Association on the basis that endless prevarication will only further depress the British farming industry. There is also a licensed injectable vaccine for badgers which should be used in disease hotspots until the oral formulation is available.
Vaccination is not the silver bullet to eradicate bovine tuberculosis - but it will provide cost-effective disease control! The current government policy of badger 'culling' is at best dysfunctional, and at worst likely to spread the disease to the rest of Britain. In addition it will seriously damage an important wildlife resource. Given the present policy is ineffective or counter-productive, unpopular among the public, and scientifically unjustified, we can only ask why is it being pursued?
For a full review of badger culling and cattle tuberculosis, along with links to all the sources, go to InfluentialPoints.
Bob Dransfield is a senior partner in InfluentialPoints.LLP with extensive teaching and consulting experience in biostatistics. He has a degree in zoology from University of Bristol, and a doctorate in population dynamics from Imperial College, London. InfluentialPoints produces a biostatistics course using R, the first unit of which can be downloaded completely free from InfluentialPoints
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