Learning from history about tuberculosis in cattle: Part 1

Here in Britain some cattle (Bos primigenius) get bovine tuberculosis (bTB) and we want rid. You might choose to follow my tag ‘tuberculosis’ for other posts on this. Here’s a list of notifiable diseases affecting livestock in Britain.

A few days ago I reminded you that John Bourne chaired the team which gave us this: ‘A Science Base for a Sustainable Policy to Control TB in Cattle’. Damian Carrington at the Guardian reported Prof Bourne saying that new rules on cattle movement, introduced at the start of this month, are ‘a move in the right direction’ but too weak. According to Prof Bourne, we need ‘even stricter biosecurity’. We need to learn from our history and from Australian history.

Lewis Clarke at the Tiverton People wrote about the history of bTB and badger culling in Britain. This is a viewpoint from Tiverton in the South West of England, also known as the West Country. Mr Clarke says that cattle testing was introduced nationwide in 1935. I think that the threat of war may have had something to do with that. A country at war needs safe food. After the war, test-and-slaughter became compulsory in the 1950s when over 60% of cattle herds were infected. The test-and-slaughter programme was a hard thing for farmers but it worked: bTB was ‘practicably eradicated down to a level of less than 1%. By 1960, the disease was confined to a few pockets in the South West of England, and remained manageable.’

Twenty years later, says Mr Clarke, ‘In the 1980s badgers were identified as carriers of… Mycobacterium bovis [the bacterium which causes bTB]… and instances of the disease started to rise.’ That trend has continued. The Department for Environment Food and Rural Affairs (DEFRA) says, ‘The trend of cattle TB incidence in England has been rising for 25 years’ (scroll down for maps).

Why that rise in bTB? I don’t think the titchy M. bovis was reading what scientists wrote. Perhaps it took advantage of inadequate testing of cattle, and of too-frequent moving of cattle around the country.

Still, you can understand why badgers got the blame. There’s evidence that badgers can transmit bTB to cattle. In 1997 John Krebs wrote, ‘The sum of evidence strongly supports the view that, in Britain, badgers are a significant source of infection in cattle. Most of this evidence is indirect, consisting of correlations rather than demonstrations of cause and effect.’

Every science student learns that correlation doesn’t mean causation. The West Country has plenty of wonderful food as well as plenty of badgers and plenty of bTB. But nobody’s blaming the cream-topped scones for the tuberculosis.

Later Prof Krebs (now Prof Lord Krebs, or Baron Krebs – I don’t really understand the peerage system!) changed his opinion about bTB. Like any good scientist, he’s open to new evidence. That evidence came after the Government ordered a trial badger cull in response to the Krebs Report of 1997. That was the Krebs Trial or the Randomised Badger Culling Trial.

In the Tiverton People article I linked to above, Mr Clarke says, ‘When the Randomised Badger Culling Trial ended ten years after it began… key conclusions were… that badger culling can make no meaningful contribution to cattle TB control… [and] that weaknesses in cattle testing regimes mean that cattle themselves contribute significantly to the persistence and spread of the disease.’

In 2011, Fiona Harvey at the Guardian quoted Prof Krebs. He said that his trial had shown that badger culling was “not an effective policy” and would be a mistake. In 2012 Prof Krebs joined other scientists in urging DEFRA to abandon its plan to cull badgers. Alistair Driver at the Farmers Guardian quoted those scientists saying that a badger cull will spread bTB.

At DEFRA, Ian Boyd is the chief scientific adviser and Nigel Gibbens is the chief veterinary officer. In October 2012 Prof Boyd and Dr Gibbens wrote, ‘Research in England has demonstrated that cattle and badgers transmit the disease to each other. It also showed culling badgers leads to a reduction of the disease in cattle if it is carried out over a large enough area and for a sufficient length of time.’

I’ll write more about bTB but for now, I’ll leave you with words from DEFRA. ‘A number of different measures have been tried to control the TB in cattle by culling badgers. None of these were entirely successful.’


About argylesock

I wrote a PhD about veterinary parasitology so that's the starting point for this blog. But I'm now branching out into other areas of biology and into popular science writing. I'll write here about science that happens in landscapes, particularly farmland, and about science involving interspecific interactions. Datasets and statistics get my attention. Exactly where this blog will lead? That's a journey that I'm on and I hope you'll come with me.
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2 Responses to Learning from history about tuberculosis in cattle: Part 1

  1. Finn Holding says:

    I still don’t understand why there is a policy of imposing export restrictions on cattle with bTB antibodies. If they have been vaccinated and the relevant regulatory documentation is in place why is export problematic? Surely it would make sense to vaccinate the national herd with a proven efficacious vaccine rather than pander to the ‘pseudoscience’ surrounding badgers and TB.

    Why is it that there is a badger vaccine for TB but not a bovine one? It would be impossible to adequately vaccinate the badger popoulation for the same reason a cull wouldn’t work: according to DEFRA 70% (I think) of the badger population would need to be destroyed to curb bTB – but no one knows how many bagders there are! So neither culling or vaccinating the badgers can realistically be expected to provide a solution.

    It seems to me that the badger cull is focussing down on one aspect of bTB and throwing a smokescreen over the others thereby preventing a proper and effective solution

  2. argylesock says:

    I think the difficulty with bTB antibody-positive cattle is that there’s no test to distinguish an infected cow from a vaccinated one. I should research this more. But I think the trouble with infected cows is that their milk can be infectious to human consumers, and that their breath can be infectious to other cows. Importing such a cow to a bTB-free zone, eg Australia, would mean losing the bTB-free status.

    Here’s what DEFRA says about bovine vaccination http://www.defra.gov.uk/animal-diseases/a-z/bovine-tb/vaccination/cattle-vaccination/ Basically, it more or less works, but it needs more development.

    Where did you get that figure of a need to cull 70% of badgers to curb bTB? If you can find the original paper, I’ll try to find time to read it. Meanwhile I still have more to say about bTB on my blog here, esp about farmers’ points of view. NFU is pro-cull as you know, and I want to be clear about why.

    Unless and until my opinion changes, I agree with you about the smokescreen.

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