"in the absence of a wildlife reservoir, the Intradermal skin test and slaughter of reactors to it is all that is necessary to control bovine tb".The intradermal skin test is OIE and EU approved and used as a primary tool for identification of a candidate animal's exposure to tb bacterium all over the world - with absolutely no problems.
PQ's gave us the answer that "in the absence of a wildlife reservoir, the Intradermal skin test and slaughter of reactors to it is all that is necessary to control bovine tb".
Its sensitivety and specitivity to m.bovis are in the high 90's% (97 and 98 from memory) - when used as a herd test. (This drops to 70% when applied to an individual animal) and the Dexter calf was part of a routine herd test.
It is not designed to show clinical tb. It shows an animal's immune response to exposure to m.bovis, (in the UK by comparison to m.avium) which may or may not go on to develop into lesions. That process depends on the size of the dose and incubation period hence post mortem confirmation.
In our almost 5 year breakdown, 40 out of 43 carcasses of much valued incalf dairy cattle and yearlings had no sign (or culture) of the disease. But contact with it, they certainly had had - in spades. And in a herd which had bought in no cattle, it should not have been there.
Frankly the lady does not have a leg on which to stand. The calf has tested positive to exposure to a dose of m.bovis. And having become so high profile, Defra testing 4,5 million cattle per year cannot afford to repeat test cattle that have actually 'Reacted' to a world wide diagnostic tool.
She would be better to let the calf go, and concentrate on the story of the rest of her herd which will face tests every 60 days until they test clear. And if a pernicious drip feed of badger m.bovis is infecting them, that could take a considerable time - as we found. And cost the taxpayer a lot of money, and put at risk other susceptible animals, cats, dogs, ferrets, free range pigs and the lady herself.
Think of the cattle as sentinel 'canaries'. We would have lost a heap of coalminers, if the NCB had strangled any moping sentinel pit canary, while ignoring the presence of fire damp. But that is exactly what this government is exposing the cattle to - and everything else that can be infected with tuberculosis.
email from farmer 10/1/06