Tuberculosis (TB) in humans is a disease of poverty. The causative agent, Mycobacterium tuberculosis, spreads between people in droplets breathed out or sneezed out. I’ll never forget the disgust on my tutor’s face when she described handling sputum samples but if your science concerns TB, you’re going to have to deal with sputum. And this is how come it’s a disease of poverty. People in overcrowded, poorly ventilated homes or shelters are at risk of droplet infection. In the rich world TB has declined dramatically but now that people move around the world so much more than we used to do, TB in the rich world is back.
What has this to do with cows (Bos primigenius) and badgers (Meles meles)? Well, humans can also be infected by the bovine species of TB, Mycobacterium bovis. When milk isn’t pasteurised people can pick up M. bovis by drinking milk. When cattle are overcrowded in barns or during transport M. bovis can spread between them by droplet infection. Here’s a list of notifiable diseases affecting livestock in Britain.
Wildlife species can be reservoirs of M. bovis. Here in Britain that’s mainly the badger (Meles meles) and there’s evidence that M. bovis is being transmitted between badgers and cattle.
Is a cull of badgers part of the answer? Well that’s a different story. I’ve noticed how emotional people get about the badger, because it’s so cute and because it’s been part of so many children’s stories. I myself, growing up with nature posters all over my bedroom wall in the 1970s and 1980s, dreamed of seeing a wild badger one day. Then when I’d grown up and M. meles had been a protected species since 1973, with protection strengthened in 1992, it was a thrill to see badgers at dusk one time when I was camping.
If I’d owned the cattle which grazed nearby, perhaps I wouldn’t have felt such thrill. But should I have invited people sanctioned by the Department for Environment Food and Rural Affairs (DEFRA) to come and shoot the badgers? Or should I have reconsidered my farm buildings?
Every farmer I know takes buildings very seriously, making sure there’s good ventilation to minimise the risk of respiratory diseases. TB is one of those diseases and there are many others affecting livestock. So no, I don’t think that those cattle will have been housed in a cramped damp barn.
But I think those cattle might have been transported too far and too often in cramped trucks. DEFRA says that livestock transport vehicles need good ventilation. Why are cattle moved around so much? That’s a topic for another blog post.