Sir

The UK government's strategy for controlling bovine tuberculosis (TB) is to work with stakeholders to reduce the economic impact of the disease and to maintain public-health protection, as well as animal health and welfare. In a nationwide programme, the Department for Environment, Food and Rural Affairs is investing between £74 million and £99 million a year on continuing cattle surveillance and control, slaughterhouse inspections, heat treatment of milk, occupational-health controls and monitoring for human cases (see http://tinyurl.com/578s5x).

The number of infected cattle herds increased from 88 in 1986 to 5,539 in 2005 (P. D. O. Davies J. R. Soc. Med. 99, 539–540; 2006). However, this increase has not been mirrored by an increase in zoonotic TB in humans. Between 1993 and 2003, there were 315 cases of bovine TB confirmed in humans: a mean number of 28 cases per year. All 50 isolates of Mycobacterium bovis, the microorganism responsible, that were recovered from humans between 1997 and 2000 have been investigated (A. L. Gibson et al. J. Clin. Microbiol. 42, 431–434; 2004), and of these, 15 had not been previously recorded in the UK cattle population.

Of the human cases of bovine TB, 72% of those infected were more than 50 years old (suggesting reactivation of an infection acquired before routine milk pasteurization was introduced), and many of the remaining cases were people born abroad. That leaves only a very small number of potential cases of transmission from present-day UK cattle, of which just two have been confirmed (R. M. M. Smith et al. Emerg. Infect. Dis. 10, 539–541; 2004).

Since the introduction of milk pasteurization, TB in humans caused by M. bovis has virtually disappeared in the United Kingdom. Consequently, the disease poses a negligible threat to public health.

Why then should a major intervention programme, proposed badger culling and vaccine research now be necessary to control it? The overwhelming societal cost of bovine TB is directly attributable to the costs of running the eradication programme and the associated research into control.

In the absence of significant transmission to humans, this question urgently needs to be addressed. Controlling bovine TB should be justified only in economic terms of reducing losses in animal productivity.