Bovine bacteria

23rd January 2004 at 00:00
Rather like TB in humans, the incidence of tuberculosis in cattle, or bovine TB, has been increasing in England and Wales after a quiet period.

In the first few decades of the last century the disease raged through dairy cattle herds. In the 1930s and 1940s, about 40 per cent of cattle were found to be infected with TB. Bovine TB can be transmitted to humans and was. Approximately 2,000 people a year died because of drinking contaminated, unpasteurised milk or coming into close contact with infected cows. Altogether, 6 per cent of human TB deaths between 1931 and 1941 were the result of bovine TB.

Numbers dropped in the middle of the century and by the 1970s, tuberculosis in cows was all but eradicated. But between 1996 and 2002, the incidence increased by 29 per cent. For each of the past two years, up to 700 herds have been slaughtered by the State Veterinary Service after failing the tuberculin test, which is the standard government procedure for dealing with bovine TB. In Wales alone, 5,000 animals were slaughtered in 2002.

The reason for the rise is hotly disputed. Since the 1970s, badgers have been blamed as the source of infection to cattle; more than 30,000 have been gassed or shot in the past 25 years in a government-run cull. Badgers are indisputably carriers of TB - as are ferrets, rats, moles, foxes and deer - and transmit infection to cattle.

But the most recent research study analysing the impact of badger culls was suspended by Animal Health Minister Ben Bradshaw. What prompted this was interim findings showing a 27 per cent increase in the incidence of bovine TB in cattle near where the culls had been taking place.

The likelihood is that, as in human TB, there are a number of factors that have contributed to this upsurge. A major one is the foot and mouth epidemic of 2001. Not only were fewer herds tested for TB during that period because veterinary attention was focused on foot and mouth, but animals were kept penned up, allowing the infection to spread.

Another possible factor is that farmers are moving cattle from TB hotspots to other parts of the country before testing them. This, believes Dr Elaine King of the National Federation of Badger Groups, is responsible for the emergence of cases in previously TB-free parts of Cumbria, Denbighshire and Scotland.

But there is hope. The make-up of the genome of the organism responsible for bovine TB has been discovered by scientists in a collaborative project by the British and French. This is a major breakthrough in the search for a vaccine against bovine tuberculosis.

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