Badger Fortnight: TB

For the next couple of weeks I am dedicating Fluffy Sciences to the noble badger. Why, you ask? Well because the other day I ended up reading Defra’s independent panel report on the UK badger cull and the whole thing made me grumpy.

As someone who works both in animal welfare and in the agricultural industry, with a soft spot in my heart for cattle, I have heard a lot about Bovine TB and badgers in the past few years. I’m going to spend the next few posts telling that story, and where better to start but with Bovine TB itself? After all, without this insidious disease, badgers would be fondly remembered from the Animals of Farthing Wood, or the noble lords in Redwall. Instead they’re synonymous with James May and the word ‘cull’. An interesting turn of events.

So. Bovine TB, the villain in our tale. What are you?

When you’re reading or watching some trashy historical drama and the heroine coughs into her handkerchief, staining it gently with blood, you know she’s not long for this world. Satine, I’m looking at you. That disease is Tuberculosis, or consumption, if you’re still feeling gothic.

It’s a famous disease in science because of Robert Koch, who formulated the well known Koch Postulates, a set of rules to identify the causative pathogen of disease. While still very much remembered, they have been supplanted with other rules better capable of identifying things like parasites and even non-active infections.

  1. The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
  2. The microorganism must be isolated from a diseased organism and grown in pure culture.
  3. The cultured microorganism should cause disease when introduced into a healthy organism.
  4. The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

Koch identified the agent of TB, Mycobacterium tuberculosis, and he received a Nobel Prize for his troubles. Interestingly enough, he received his prize even though for years he’d been convinced that Bovine TB and human TB were not similar, and it was his results that forced him to reevaluate this position.

Fast forward a couple of hundred years and this disease which, at one point, was causing 25% of the deaths in the world was now on the run. Almost all Brits have a peculiar little scar on their left upper arm, the BCG (Bacillus Calmette–Guérin) scar. I have had some Americans quiz me about it and it turns out Americans never had a mass BCG immunisation. You guys missed out on some quality arm punching in school.

If you’ll think back to your school days, you’ll remember a thirteen year old you suspiciously watching a nurse inject you just under the skin on your arm. A few days later they inspect the mark and then decree whether or not you will receive the BCG  vaccination.

It’s often said that if you react to the skin test it means you are already immune to TB, but this isn’t quite true. It means that your body reacted to the TB (in a healthy person this means they got a red blister bigger than 15mm in diameter) which may be because you have a previous vaccination or because your body already has an active TB infection.

Regardless, those who escaped the skin blister get called back for the vaccine. The injection goes between the skin (large ulcerated BCG marks are often an indication of an accidental subcutaneous BCG). As vaccinations go, its quite painful (I remember it being more uncomfortable than three successive rabies vaccinations) and not helped by the traditional teenage sport of punching people in the vaccination spot.

Large keloid scars can form, although latterdays these scars are not so prominent due to improved techniques. I did try to take a picture of mine for you but mine is tiny and barely shows up. The mass BCG vaccination program has recently been suspended in the UK as the disease is now considered very rare. Only at-risk groups are vaccinated now.

 

 

Despite the fact that antibiotic resistant TB is on the rise (and that this is frightening) in the UK we manage the disease in humans fairly well. Other countries, such as India, haven’t been as successful as we have in using the BCG vaccinations – and it seems to be that the disease is harder to manage in equatorial regions, for reasons I’ll not speculate about here.

However Bovine TB is caused by the very similar pathogen Mycobacterium bovis, which can cause TB in humans if they drink the unpasteurised milk of an infected animal, or if they inhale aerosol droplets (e.g. cough, spits and sneezes) of a cow.

Being someone who has been coughed, spat and sneezed on by various cows, I’m not particularly worried about this myself, even though Bovine TB can cross the species barrier, TB itself rarely becomes an active infection in the person who has it.

So why do we worry about it in cows? Well we have a strange double standard here. When we test cows, we use a skin test very similar to the one we use in humans. And, like in some humans, there is a reaction to this skin test.

And those cows which react to the skin test must be culled. You’ll remember that only a few paragraphs higher up I mentioned that a reaction doesn’t mean immunity, it just means the animal is reactive. It doesn’t mean there is an active infection, it just means the animal is reactive. Yet we cull those animals specifically to prevent the spread of the disease.

You can sell the meat of the culled animal if you want, because cooking meat kills the Mycobacterium, but you cannot tolerate a TB cow on your farm.

And this isn’t considering false negatives and false positives in the test, as no diagnostic test is perfect.

The fear is that Bovine TB will either infect or reactivate a latent TB infection in people. Because of this fear we cull any cows infected with TB. Defra have also produced what they optimistically call a leaflet (at 21 pages) of ‘What happens if TB is identified in your herd’ which remind me of those Simpsons leaflets ‘So You’ve Ruined Your Life’.

 

The moment a cow reacts to the skin test the herd is classed as suspect and moving cattle out of and into the herd is restricted. Any reacting animals must be isolated from non-reacting animals and culled. The milk is to be dumped.

The reactor cows are tested post mortem, but even if your reactors show no clinical signs of TB, your herd status is still Officially TB Free Suspended. You will need a clear test (or two clear tests if TB was found in your reacting cows) for your Official TB Free status to be reinstated.

If you have a TB farm you also have restrictions on where you can spread your slurry and on what you can do if your cows die on farm.

It is, in short, a huge hassle, resulting in cow deaths and loss of farm profits, as well as posing a health risk to humans.

 

It is with these facts that the government turned its attention to badgers, and that, dear readers, we will discuss next week.

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One thought on “Badger Fortnight: TB

  1. Pingback: Badger Fortnight – The Solution? | fluffysciences

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