17 Jun 2008

Badger and TB: is the answer obvious?

badger_small.gifThe locally based group, Stop the War on Badgers has lost their website for a while so I've been asked to enclose the key information of their position below as it looks like a decision on culling is imminent from the Government. See also previous blog entries on this topic by using the search engine.

Copyright photo: Badger by Tony Evans Nature Picture Library reproduced with permission from Stop War on Badgers

The main thrust of the groups' current message is along the lines of what the Badger Trust are doing. This points out the differences in TB policy and results in different parts of the British Isles.

Republic of Ireland: killing loads of badgers - no effect on bTB levels.
Wales: now devolved - have taken the progressive step of allowing policy to be dictated by a powerful union (The Farmers' Union of Wales). Remains to be seen what the results will be, but Badger Trust has mounted legal challenge to this.
Northern Ireland: Quietly got to grips with backlog of bTB tests after Foot & Mouth, and have introduced sophisticated cattle controls. No badger culling. bTB dramatically down.
England: NFU want us to follow example of Rep of Ireland (duh). Will the govt cave in?

This message is really simple (for most of us), and people can be left to draw their own conclusions. Here are some further comments from a Stop the War member:

The Badger Trust is also highlighting lack of controls when moving cattle to shows. Recent outbreaks in allegedly 'closed herds' have been (on closer inspection) in cases where cattle have been sent to shows to socialise with loads of other (untested) animals.

But any alternatives to the badger theory are literally unthinkable for the NFU and their allies (including in the veterinary profession) because of the possible implications - that it could be these very people who have caused the problem, by their forgetting of the importance of cattle controls, specifically after the 2001 FMD outbreak, which is when bTB really exploded.

Their threats not to cooperate with (necessary) cattle controls unless they are also allowed to kill badgers (unnecessary) amounts to a last-ditch attempt to manufacture evidence. (bTB will eventually go down, thanks to renewed cattle controls, but they will say it was because they killed badgers. But the Northern Ireland example should show this up for the con that it is, which is why what's happening there should be brought to the attention of as many people as possible.)

And here is stuff from their website: Bovine TB biosecurity explained (November 2007)

Most of the confusion in the bovine TB debate arises from not understanding the nature of the disease, and how it was controlled in the past.

Just as with human tuberculosis, bovine TB is a lung ‘consumption’. It has two main stages:

1) an advanced/infectious stage, where there are visible lesions (VL) in the lungs, which will release bacteria into the sputum. This stage is detectable either by X-ray or by examining the dead animal after slaughter – but it tends not to be picked up by the bTB skin test.

2) a latent/incubating stage, which is hard to detect in a slaughtered animal, as there are no visible lesions. At a very early stage, it may also be missed when examining a tissue sample under a microscope, as there will only be very small numbers of Myobacterium bovis bacteria present.

The way to contain and eventually eliminate the disease is to identify cases at the latent stage and remove them (by slaughter or chemotherapy) before they progress to the advanced stage, when they can pass the disease on.

But the tools for identifying this latent stage are imperfect. The bTB skin test only works in the middle range of the disease (see below). Also, if an infected cow has recently calved it can temporarily give a false negative.

The way round this limitation is to repeat the skin test at intervals of ONE YEAR or less. This will catch most cases before they reach the advanced/infectious stage.

This is exactly what happened in the 1960s. The infectious reservoir of VL cases (hard to detect in living animals) dwindled over time, as these animals were sent to slaughter (believed bTB free until examined at abattoir). Meanwhile annual testing stopped the reservoir being topped up.

By the early 1970s this strategy had cleared the disease from most of Britain, and cut cases to a tiny fraction of their former levels (see below). (The remaining bTB ‘hotspots’ were limited to the South West, an area of particularly high cattle density and intensification, where biosecurity measures should also include attention to such things as the safe disposal of potentially infectious slurry.)

But if the test interval is extended beyond one year, the disease will start to get out of control, as more animals reach the advanced/infectious stage.

This is exactly what happened from 2001. During the Foot and Mouth disease (FMD) epidemic, all bTB tests were stopped, and the backlog was not properly addressed until 4 years later – after untested cattle had been moved around the country to restock depleted areas. The results of this disastrous ‘experiment’ speak for themselves.

However, after 36 years of repetition (from 1971), the received wisdom among certain influential groups remains the same: that badgers are the main source of bTB. This belief is why basic cattle biosecurity was abandoned after FMD, and why there is continuing resistance to concentrating on the necessary measures now.

1 comment:

Anonymous said...


The Great Badgers and Bovine TB Debate has rumbled on for 37 years and has now come to a head with the current cattle TB crisis. Farmers and vets are certain badgers are the main reservoir of TB and cause of new and repeated herd breakdowns so insist a cull is essential. But everyone has forgotten how TB works in cows and why badgers got the blame in the first place. It seems quite beyond belief, but everyone needs to rediscover the fact that TB IS an infectious disease, and the tests are far from reliable.

TB spreads within and between herds if unchecked. So the whole point of annual testing is that it removes cases before they can pass TB on, and herds under restriction are not exporting TB carriers. So TB shrank from countrywide down to tiny southwest hotspot pockets by the early 1970s, without any badger culls. Alas, the second impact of intensive testing is that cases are found so early that they are unconfirmed being without lesions or M.bovis on culture … but at least 80% of such cases DO in fact have TB. In addition tests completely miss early and late TB cases so there is a huge “Undisclosed” reservoir of cattle TB. And that is why Old Brock got the blame by default.

With intensive annual testing in hotspots since the war, it seemed as if cattle were not the main infectious source of TB. Hence the lack of testing due to Foot and Mouth in 2001 was a one off disastrous “experiment”. More cases got to the infectious stage and TB exploded out of control with 30,000 reactors in 2005: twice the level as at the start of the Area Eradication scheme in 1961. Local movement of cattle expanded the former hotspots into one big hotspot in Devon/Cornwall. And worst of all, many big dairy herds now have non-reactor or anergic active spreader cases so have been under restriction since FMD or longer. This needs either a blood antibody test (Brocktest) or DNA PCR on faecal swabs (Citizen letter 9th June). Zero tolerance on overdue herd tests and more cattle testing has begun to reduce the crisis, repeating the 1960s effect, without any need for badger culls.

So, what of Prof Bourne and the ISG’s report last year on the Krebs culling trial? They claimed that proactive culls reduced cattle TB by 23%, but due to perturbed badgers increased it by some 20% (reactive) to 25% outside proactive areas. But this is complete and utter nonsense, since out of 11,000 badgers culled only 1515 had TB; in nearly half the 51 proactive culls there were 15 or fewer with TB out of 100 sq km, and in total ONLY 166 with advanced lesions which might have been a risk to cows (though it is still unclear how badgers are supposed to give cows a respiratory lung infection). The rises in TB happened BEFORE the reactive cull and both inside and outside NO CULL areas and was part of the national upsurge. Their latest paper just out claims that the perturbation effect has stopped in outside areas, and a further drop inside proactive areas, but they cannot see that this is because intensive cattle testing is working. The ISG study is the £50 million pseudoscientific CON of the century!

Rather ironically, the doubling of cattle TB due to FMD also doubled the spillover TO badgers. With similar effects in Wales in new hotspot areas:-

Innocent Bystander, Victim not Villain.

M Hancox,