In their replies to our Correspondence on bovine tuberculosis (TB) 'Does risk to humans justify high cost of fighting bovine TB?' (Nature 455, 1029; 2008), Noel Smith and Richard Clifton-Hadley ('Bovine TB: don't get rid of the cat because the mice have gone'; Nature 456, 700; 2008) and Stephen Gordon ('Bovine TB: stopping disease control would block all live exports'; Nature 456, 700; 2008) argue that these costs are indeed warranted.
The current surveillance system for bovine TB may remove cattle at an early stage of infection, as Smith and Clifton-Hadley suggest, but the UK cattle herd is generally young and bovine TB is a chronic disease. Hence, in the absence of control, very few cattle would be likely to reach the advanced stage of the disease at which airborne transmission might, at least in theory, be increased. It is also worth noting that in the early twentieth century, before bovine-TB control was instigated, almost all cases of zoonotic TB in the United Kingdom were non-pulmonary, and most of the small number of pulmonary cases seemed to come from haematogenous spread rather than airborne infections (A. S. Griffith Tubercle 18, 528–543; 1937). With larger farming enterprises and fewer farmers, the at-risk population would be a fraction of that prevailing previously. Human exposure would therefore be likely to remain very low, even in the absence of bovine-TB control.
Gordon claims that abandoning bovine-TB control would bring all live exports to a stop, and he compares Britain's bovine-TB programme to that put in place for foot-and-mouth control in 2001. But foot-and-mouth disease has a devastating economic effect on livestock that goes beyond merely closing down exports, and the cost of the 2001 UK outbreak was a one-off, non-recurring charge. Bovine-TB control is costing up to £99 million (US$140 million) a year and, according to Gordon's own data, live exports have a value that is considerably less.
In addition, the ongoing bovine-TB programme in the United Kingdom is failing to eliminate the disease. Those who propose to spend large amounts of public money on bovine-TB control need to demonstrate the economic and/or public-health benefit; so far, such evidence has been lacking.
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Torgerson, P., Torgerson, D. Benefits of stemming bovine TB need to be demonstrated. Nature 457, 657 (2009). https://doi.org/10.1038/457657d
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