Wednesday, August 25, 2010

An anniversary

One of our contributors has forwarded the following text:
"And now we are fortunate enough to possess a method that enables us to recognise very early if an animal is infected with Tb or not, viz the tuberculin test.

Tuberculin is an extract of tubercle bacilli cultivated in bouillon with glycerine. The bacilliare killed so that the fluid cannot infect, but it has, when injected under the skin of an animal, the marvellous property of producing a typical fever, which appears after some hours and lasts about 12 – 16 hours – so called reaction – if the animal is affected with tuberculosis even in the slightest degree, while a healthy animal is not at all influenced by the injection. Tuberculin was for the first time prepared by Koch in 1890.

He hoped to have found a remedy to cure tuberculosis, and tuberculin seems indeed to have some curative influence, though not as much as hoped. But its diagnostic property is recognised by all, and the tuberculin test is used on a very large scale.

It is true that tuberculin is not absolutely infallible. Very old small tubercular deposits enclosed in a thick layer of fibrous tissue sometimes fail to call forth a reaction, but it is of no practical consequence, because such deposits will as a rule do no harm. A worse thing is that animals suffering from TB in a very high degree sometimes cease to react. This fact has done much harm, because such animals will usually have open tuberculosis, and their presence in a healthy herd may therefore occasion much contamination, but when the person in charge is aware of the danger, it will as a rule not be difficult to recognise the disease by clinical examination.

It is still worth mentioning that repeated injection of tuberculin may in some animals provoke immunity to the test, which may be used by a cattle dealer with intent to defraud."

Several pages are devoted to the development and use of the 'Tuberculin Test', which originally used m.tuberculosis as its base. Later this was changed to a derivative of m.bovis (AN5 strain) and in the UK, an m.avian comparative jab was added.

The reference to old walled up lesions from previous exposures is also mentioned in the CVO reports after the eradication sweeps of the 1950s and 60s., where it was expected that some cattle would present at slaughter with such scars, over the next decade. After which time, the cattle herds of the UK, in parallel with many other countries (and in the absence of a wildlife reservoir) would have eradicated Tuberculosis.

The quote is taken from ‘The Standard Cyclopedia of Modern Agriculture’ vol X11 TRI – Z , which was published in 1911 - a century ago.

Happy Anniversary.

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