Tuberculosis is a disease affecting animals and humans. In cattle it is caused by Mycobacterium bovis. However M.bovis can also cause disease in other types of animals, for example badgers and deer, and humans.

History of Tuberculosis
In the 1930s tuberculosis was present in approximately 40% of dairy cows in the UK. At that time the cattle were kept fairly closely confined in conditions of poor ventilation, which allowed spread of the disease. The tuberculous lesions in the udders allowed bacteria to enter the milk and in the days before pasteurisation this posed a great risk to humans drinking the milk. In fact over 50,000 cases per year were occurring in the population. Compulsory testing was begun with slaughtering of infected animals. In addition milk was pasteurised to further reduce the human risk, with all untreated milk containing a warning to that effect and herds supplying untreated milk subjected to a strict TB control testing regime.

Current Status
Cases of tuberculosis have now started to increase in the UK, with exact numbers difficult to know precisely. Numbers are difficult to quantify because of the backlog that has arisen in TB testing following the recent Foot and Mouth disease outbreak when all testing stopped. However up to the end of 2000, around 7,000 cattle per year were slaughtered as reactors. There are concerns that the disease is spreading into new districts, with some areas affected where TB has not been seen for many years.

Public Health Issues
Bovine tuberculous is potentially transmitted to humans via the meat or the milk. However cases are rare since the bacterium is killed by pasteurisation in milk and by cooking in meat. Human infections with M.bovis have been seen which have either been caught abroad or occur in often elderly people drinking contaminated raw milk. There is no evidence of foodborne infection in the UK. There does remain a small risk to workers, for example, in slaughter plants handling infected cattle carcasses being infected by cuts or inhalation. The programmes in place to test the cattle population removes for slaughter those cattle suspected and confirmed of having the disease.

Tuberculosis Transmission and Epidemiology
The exact details of the transmission and epidemiology of TB are not known with complete certainly. However there is very strong evidence that badgers are implicated and are in fact the main wildlife reservoir of the disease. Measures can be taken to reduce the likelihood of cattle being infected by tuberculous badgers, by limiting contact between cattle and badgers. For example; by fencing off sets to prevent cattle investigating them, burying dead badgers found on the farm and preventing badgers getting into farm buildings, feed stores, water troughs and silage pits. The likelihood of cattle infecting other cattle can be reduced by adequate ventilation in buildings, checking stocking densities and spreading slurry over fields not grazed by other cattle. Where it is not possible to keep a closed herd then all bought-in cattle should be TB tested and subjected to quarantine. Extensive epidemiological research is currently being done to elucidate what factors influence whether or not a herd has TB, how it is spread (faeces, urine, milk, aerosol etc ) and the relative importance of cattle to cattle, badger to cattle and cattle to badger interactions. The significance of other wildlife, for example deer, in the disease is also being investigated.

Cattle Control Measures
A testing routine, using a highly sensitive test ( the comparative intradermal skin test ) is in operation for TB surveillance purposes. All cattle, with the exception of beef fattening units, are tested at intervals of 1,2,3 or 4 years depending on the farm's geographical area and its history. Movement restrictions are put in place where reactors or inconclusive reactors are found or where tests become overdue. All reactors are slaughtered and in-contacts traced and tested. Research is being done into the production of a vaccine, to be administered to cattle, but which does not interfere with the tuberculin test. The current test for TB does not differentiate between infected and vaccinated animals. Other work is looking at a test to diagnose TB in live badgers and the possible production of a vaccine for oral administration to badgers.

*   incomplete data
** provisional data

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