Why is it necessary to spend money addressing bovine TB?

A question often asked is,

"Why is it necessary to spend money addressing bovine TB when bovine TB is currently considered to be a very small risk to human health?"

Prof Christl Donnelly replied to this on the BBC's Farming Live program on 28th July 2011 as follows.

If there was no control of the animal health disease then bovine TB would increase dramatically and then it would be a huge occupational health risk. Also any failure of systems could then have potential for public health risks.