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Q&A: Bovine tuberculosis

23 Oct 07 16:39

The UK government's chief scientist, Sir David King, has advised ministers that killing badgers can help prevent the spread of TB among cattle, the BBC has learned.

Here are the answers to the key questions about TB in cattle and badgers.

What is bovine tuberculosis (bTB)?

This is the name given to the type of tuberculosis that infects cattle.

The disease, which can take years to develop, damages the animal's lungs and eventually leads to death.

There are very few clinical signs of the disease but most animals will develop lumps on their body, usually on the flanks.

Unlike foot-and-mouth disease, TB is usually only caught by a handful of cattle rather than a whole herd.

However, due to the slow progression of infection and the government's testing and slaughter programme, the clinical signs of bTB, such as weakness, coughing and loss of weight, are now rarely seen in cattle in Britain.

How many cattle die as a result of bTB?

The disease was at its worst in Britain in the 1930s when large numbers of dairy cows were infected.

At this time, many cattle were kept near large cities to provide urban dwellers with fresh milk, which meant most were confined in poorly-ventilated cowsheds. These were ideal conditions for the disease to spread.

Then, after the testing and the slaughter of those animals thought to be infected became compulsory in 1950, the numbers were reduced.

However, during the last 15 years the number of cattle dying from TB has been slowly rising.

Figures from the National Farmers' Union suggest the number of cases of bTB has risen by as much as 18% in the past year, to nearly 2,500.

How does the disease spread?

There is a great deal of debate surrounding bTB and the way it is transmitted.

It is believed to be primarily passed from one animal to another by breathing in the bacteria.

Evidence suggested that badgers were a source of cattle TB, but there was uncertainty over how much the animals contributed to the infection rates.

In November 1996 Professor John Krebs and the Independent Scientific Review Group began a study on behalf of the government into the link between bovine tuberculosis and badgers and whether culling badgers would work.

Controversial badger culling trials - named the Randomised Badger Culling Trial - were introduced and produced mixed evidence on the likely impact of culls.

The most recent study by the Independent Scientific Group, published in June, also suggested badgers played a role in the spread of bTB, but warned that culling would have to be so extensive it would be uneconomical.

Meanwhile, conservation groups, including the Badger Trust, argue the disease can be contained by improving the cattle-testing regime and introducing tighter restrictions on cattle movements.

What is the government doing to control the problem?

The government is currently considering whether to introduce a cull of badgers in England, although a consultation mounted recently by the Department for Environment, Food and Rural Affairs suggested public opinion is firmly against such a move.

Wales, Scotland and Northern Ireland would make their own decisions on any prospective cull.

Farmers say the spread of cattle TB by badgers is destroying the industry and that culling would control it, while conservation groups cite research suggesting that targeting one site would only cause badgers to flee to other farms.

In addition, a £1m field trial of a vaccine to combat tuberculosis in badgers was launched last year.

The government already carries out routine testing for TB on cattle every one, two, three or four years depending on how widespread bTB is in a particular region.

All cattle in England, Wales and Scotland also have to be tested before they are moved.

Can the disease spread to humans?

Bovine TB can be passed on to humans but instances of this happening are very rare, mainly due to the introduction of pasteurised milk.

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