Bovine Tuberculosis

TB in cattle

Tuberculosis (TB) is a serious disease. As 'consumption' it was a major cause of death in Britain before the invention of antibiotics and it continues to be a major problem worldwide. The main disease in humans is caused by Mycobacterium tuberculosis and nowadays only about 1% of TB cases in humans are caused by Mycobacterium bovis(Bovine Tb) but in the 1930's it is estimated that 2,500 people died from M bovis in the UK each year. Closely related bacteria cause TB in birds and Leprosy in humans.

Nearly all warm blooded animals are susceptible to M bovis to some degree, this complicates controls. TB is hard to treat with antibiotics and there is no satisfactory vaccine for M bovis. Infected cattle are culled and the whole herd put under restrictions. They are retested frequently until it is certain that the disease has been eradicated and only then is the herd allowed to return to normal production.

TB is usually spread by sneezing and coughing. It is also spread in other bodily fluids. The usual cattle to human route for M bovis infection is via 'raw', untreated, milk.

M bovis is destroyed by heating. This is why pasteurisation of milk was introduced and it is pasteurisation that must be credited with the greatest improvement in human health.

Cattle usually catch TB from other cattle and it is for this reason that there are now strict controls on their movement. Careful records are kept to aid tracing outbreaks back to their source. Unfortunately wild deer and badgers are also prone to the disease. Deer are not thought to be a great risk to cattle as they tend not to mix with them often. Unfortunately badgers are frequently found foraging around cattle and may use the same water troughs and mineral licks. It only takes one chance encounter with an infectious badger to transfer TB to an entire herd.

In the past badgers were culled in TB infected areas and a high degree of control resulted. So much so that bovine TB became rare and badgers in uninfected areas were allowed to multiply. The rules were changed and badger culling in infected areas stopped. It is probable that this permited a permanent reservoir of disease which has now spread so that bovine TB is again a significant problem for British cattle farmers.

DEFRA have an extensive set of pages on bovine TB