Bovine Tuberculosis: should we be worried?

Continuing on the with the theme of deadly microbiology, let's take a look at Myobacterium bovis, or Bovine Tuberculosis. The bacterium has received A LOT of press coverage here in the UK, and for good reason. In 2012, 38,000 British cattle were slaughtered because they tested positive for the disease. This is because bTB is extremely efficient at spreading through an organism. It is transmitted in the air via droplet infection (just a few bacilli in a tiny fluid droplet), and when it reaches the bronchi, phagocytes move to intercept and digest the microbes. However this plays to the bacterium's advantage, as it can move into and replicate within the white blood cell. The phagocytes continue to pour into the lungs, in a largely unsuccessful attempt to destroy the invading pathogen, and the bacilli continue to replicate inside them, and eventually a tubercle is formed. The tubercle is like an undetonated warhead, and as soon as it bursts M. bovis pours out onto the lungs, causing a potentially deadly infection. The test for it involves injecting a small amount of both avian and bovine tuberculin into the skin of an animal. If an animal is infected, it will display a localised allergic reaction (in the form of swelling) a few days after the injection. But how does the bacterium spread from herd to herd? Well, 30 years ago DEFRA discovered that badgers are carriers of bTB. The RSPCA estimates that 4-6% of UK badgers are infected, and around 2,000 die every year from the fluid filled lungs which result from a bTB infection. Badgers are being culled in the UK by trained marksmen, however there have been reports of unethical set gassings and poisonings. The only vaccination currently available for cattle; the Mycobacterium bovis Bacille Calmette-Guérin (BCG) vaccine, is illegal under EU law, as an animal injected with it is indistinguishable from an animal with bTB (obviously, the vaccination is just an inactive form of the pathogen). However the vaccination is being used to treat badgers, so there is a glimmer of hope here. Furthermore, the Environment secretary Elizabeth Truss recently launched her Badger Edge Vaccination Scheme, which supports the vaccination of badgers using  BCG, in areas around the current cull zone in Gloucestershire primarily. This creates a 'buffer zone' of healthy badgers, to stop perturbation, the movement of badgers outwards from their area of origin due to ineffective culling methods,  from spreading bTB into previously unaffected areas. There have even been cases of bTB being carried by domestic cats, which pass it to their owners!  So should we be worried? If bTB continues in this way, a whole industry will go into a spiral of decline, and Britain will lose a valuable export. However there is minimal threat to human health from the pathogen. That's good...right?