Tuberculosis in cattle and people

Here in Britain some cattle (Bos primigenius) get bovine tuberculosis (bTB). Symptoms are mild until after the bacterium (Mycobacterium bovis) spreads through the animal’s body. But even in its early stages bTB is a serious problem for the farmer.

Bovine tuberculosis is bad news for the farmer because it’s notifiable. That means that if you suspect your cattle of having bTB, the law says you have to inform a police constable or go straight to the Animal Health and Veterinary Laboratories Agency (AHVLA). AHVLA tells us about notifiable animal diseases. That agency belongs to the Department for Environment Food and Rural Affairs (DEFRA), which also shows us the current list of notifiable animal diseases. Here’s what the law says farmers must do about these diseases.

Right now, bTB is the notifiable animal disease that people are talking about. I’ve been writing about it here under my ‘tuberculosis’, ‘cattle’ and ‘badger’ tags. It’s notifiable because people can get it by drinking milk. People are talking about it because there’s a badger (Meles meles) cull going on, because some people think the wild badger is a reservoir of bTB.

This isn’t the kind of tuberculosis people give each other when poor and overcrowded. That’s Mycobacterium tuberculosis, the classical human TB that remains a problem in poor countries and that’s increasing in some rich countries. We know these are two different diseases because, as Animal Research Info explains, the great Robert Koch discovered that TB in humans and cattle are caused by different bacteria.

Do people in rich countries actually get bTB? BovineTB, a website ‘looking for reform of a costly and misguided system’, says the answer’s not very often, especially not now.

That article quotes Professors Paul and Roger Torgerson saying, ‘In the UK, cattle-to-human transmission is negligible. Aerosol transmission, the only probable route of human acquisition, occurs at inconsequential levels when milk is pasteurised, even when bTB is highly endemic in cattle… Before milk pasteurisation, M. bovis was isolated from 8% of churn samples and almost all 3000-gallon tankers suggesting widespread exposure to bTB. Even then most did not get the diease. Since milk pasteurisation was generally introduced in the UK in the early 1960s, bTB has declined drastically.’

In fact, say those professors, bTB control in Britain is now irrelevant. Here’s their science.

I’ve more to say about TB but this is enough for today. Here in my well-ventilated home, I’ll sip some more tea with pasteurised milk.

[Edit] My fellow blogger Tegan Tallulah at Earth Baby is not impressed by the badger cull. She says, ‘Because cattle are kept in such large herds, the disease spreads rapidly and the centralised food system means it’s spread around the country – and beyond – quickly as well.’ Tegan also says, ‘Why the government have decided to completely ignore the study that was commissioned, I have no idea. I can only imagine it’s because they can’t think of anything better to do, and culling badgers makes it look like they’re dealing with the problem.’ I say it’s a lot to do with the power of the National Farmers Union. I’m gestating a post about the vaccine against TB; hopefully I’ll be able to shed some light with that.

About argylesock

I wrote a PhD about veterinary parasitology so that's the starting point for this blog. But I'm now branching out into other areas of biology and into popular science writing. I'll write here about science that happens in landscapes, particularly farmland, and about science involving interspecific interactions. Datasets and statistics get my attention. Exactly where this blog will lead? That's a journey that I'm on and I hope you'll come with me.
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10 Responses to Tuberculosis in cattle and people

  1. beeseeker says:

    Good to know the distinctions between different “strands” of TB.

  2. Finn Holding says:

    That’s an interesting paper Sam, it looks like basic food prep (pasteurisation) and good hygeine are what’s required. Can’t see Patterson buying that though.

    • argylesock says:

      Yes that’s what Profs Torgerson say. You mean their paper, don’t you? It seems that, if milk is pasteurised, the people most at risk of getting bTB are people who handle cattle and therefore inhale their breath.

      This leads me to remember my recent post about bTB in Ireland. One of the articles I linked to there said that Irish people are more often involved in agriculture than British people. Therefore that Irish people are more ‘able to understand’ the ‘need’ to shoot badgers. (Hope that’s an accurate quote – the article’s available from my link in that post.)

      I’m chewing over that idea, aware that I could be accused of xenophobia or something, but open to learning. Just now, having learned that bovine-to-human transmission of bTB isn’t likely *if milk is pasterurised* I wonder whether Irish farmers and farm workers get bTB by inhaling cows’ breath, or by drinking unpasteurised milk. Or whether those people tend to get bTB at all.

  3. This is a really informative post, I learnt a couple of new points on the subject. Thanks for mentioning my article, I’m glad you liked it. On the topic of badger vaccines, I’m intrigued but don’t know much about them, Some animal conservation groups are pushing them as a humane alternative to culling. My mother is strongly against the vaccines as she’s convinced badgers aren’t even the problem. I’d like to know more and I await your next post!

    • argylesock says:

      You’re welcome. I don’t think there’s much public knowledge about the TB vaccine, but the info’s available, so I’m enjoying writing my new post about it.

      There was something in your article about bTB which I didn’t want to comment on, for fear of seeming rude. You said that overcrowding cattle leads to bTB ‘spreading through the country and beyond’ or words like that. It’s the ‘and beyond’ remark that I disagree with. TB reactors (cattle which come up positive on the skin test) aren’t exported. The current vaccine makes uninfected cattle into reactors. There’s science underway to change that, improving the vaccine by something called a DIVA test.

      Will write properly!

      • Sure, I was under the impression that cattle that had the disease but had not been identified as such could still be exported. But that could be incorrect, in which case I will edit my post.
        Look forward to reading it!

  4. Pingback: How people get bovine tuberculosis. Or don’t get it. | Science on the Land

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