We reproduce it here and recommend - if you don't already do so - that you make regular visits to the TB blog site
The Tuberculin test is in fact, a very good test, and certainly the best we've got at present. We actually get an extremely small number of false negatives (animals that are infected with TB that don't show as Reactors) and they're usually found to have developed TB extremely badly, affected by BVD, or other conditions which damage or destroy the immune response of the animals. The fact that an animal reacts to the test, does not necessarily mean the animal is clinically infected - it has the antibodies to the disease, hence the reaction.
The fact that we don't find Visible Lesions does not mean the animal isn't infected. A bovine is a large animal to PM, and we're only allowed around 5-8 minutes for performing a PM, so the most common sites are targetted, using (palpation) manual feeling of the lungs, and knife to cut organs and lymph nodes open for examination by eye. A TB lesion in a cow can be the size of a grain of sand - using the Mark 1 eyeball - not easy to spot and easily missed. Culturing TB by VLA is to say the least rather hit and miss. An animal will react to the test if it has been exposed to TB and developed the antibodies.
By far the majority of VLs that are found are what we refer to as "closed" cases - not getting to the outside world, less than 5% (probably nearer 2%) of PM'd cattle are "open" cases, in Lungs, Kidney, Liver or Udder, where the infection can spread to the outside world and cattle to cattle, or cattle to wildlife (ie the Holstein/Friesian foxes). Cattle moving from the west country were blamed for introducing TB to Cumbria and other places post FMD, but spoligotyping (strain) of the TB showed to be different to the west country type - therefore home-grown more locally. Look at the number of closed herd animals that become Reactors. Cattle are tested so frequently that very few are badly infected with TB. Unfortunately B&W foxes are not tested...........Badgers are extremely susceptible to bTB, but don't die of it very quickly, once infected they produce huge amounts of the organism, which they spread as they move along, constantly dribbling urine as they go, and in their faeces and saliva. They gradually get sicker and sicker, eventually being forced out of their sett and have to go elsewhere.
Farmers are criticised for their lack of bio-security, yes you can keep cattle away from known badger dung pits; but you can't tell where they've been dribbling, and you certainly can't keep badgers away from cattle, and out of their housing in any practicable/affordable way. Feed and drinking troughs are an absolute Mecca for B&W foxes - who's going to refuse a free meal! Maize clamps are a huge attraction to badgers, which get driddled on and infected.
Cheeseman and Bourne have lost all credibility in my eyes. The Krebs trials - what a farce, and a misinterpretation of the scientific facts. Wildlife Unit staff in Reactive trapping areas, only allowed to put traps out for 8 days - the badgers don't get the chance to get used to the traps, so yes there's bound to be disturbance - a sett with 6 accesses would have 12 traps - badgers aren't that thick they know something's different! Many setts have many more entrances. It is not possible to trap out 100% (apart from being illegal under the Berne Convention), 50 -75% at most. Unless a sett is cleaned right out and kept completely empty for at least 3 months - probably nearer 12, the TB organism will still be present and waiting to infect any clean badgers. This is why the ring culling by gassing in the 60s/70s actually caused a decrease in TB incidence.
Where do you find TB in the human population? In heavily or over-populated housing, especially in warm damp conditions - any similarities with a badger sett are purely coincidental!SVS staff on the ground are as frustrated as the farming community - NO-ONE wants to see the badger exterminated - just a HEALTHY and CONTROLLED population, so they can exist in harmony with cattle. There is no natural predator of the badger - they top of the line - where there's a high badger population, there's very, very few hedgehogs, ground-nesting birds or hares - they live and breed above ground, and hence, are easy Take Away mobile food for badgers! Any mammal can become infected with bTB, and there's no doubt that deer population is becoming seriously infected and another reservoir of infection. Where do deer pick up the infection? The same way most cattle become infected - grazing or eating infected feed.
It is no good just taking and killing cattle, the wildlife reservoir has to be tackled. Some farmers have lost more than 50% of their stock, and in some cases the last of blood-lines that have been bred by their forefathers. Come on Bradshaw, bite the bullet (not much chance of that though) and order a proper, efficient cull of the wildlife reservoir as well as cattle - oh, but I forgot, that's not politically acceptable.
To quote the proverb, "Don't shoot the messenger".