Testing for TB in the cattle herd

Bovine TB is one of the most complex animal health problems currently facing the farming industry in England and Wales. It is a chronic, infectious disease of bovine animals (cattle, buffalo and bison) that mainly affects the respiratory system. It is caused by the bacterium Mycobacterium bovis (M.bovis), which can also infect and cause TB in badgers, deer, goats, pigs and many other mammals, including people.

Whilst people can be infected with M. bovis, most cases of TB in humans in Great Britain arise from infection with the human tubercle bacillus (M.tuberculosis).

This bacillus is closely related to M. bovis but it is transmitted through close contact with infected people rather than cattle. The risk of people contracting TB from cattle in Great Britain is currently considered very low. However the risk is increased where unpasteurised milk or milk products are consumed.

Anyone who keeps cattle is required by law to have them tested for bovine TB. Cattle are tested at an interval that is appropriate to both the incidence of TB infection in the area where your herd is located and the risk that your herd presents; which is related to your type of enterprise
This testing interval applies to all premises in the area, except those under restriction or those which are considered higher risk, and in these cases testing may be more frequent.

The intervals are usually every year or every 4 years, but will be more frequent if disease has been identified in your herd, a linked herd or a herd in your locality.

Sometimes lesions suggestive of TB are found in animals at routine slaughter. These are known as slaughterhouse cases. If a slaughterhouse case is identified from your herd, the herd will be put under restrictions pending further investigation and your local AHVLA office will discuss testing requirements with you.

The single intradermal comparative cervical tuberculin (SICCT) test, commonly known as the tuberculin skin test, is the primary bovine TB test used throughout Europe.

Since 2006 the Gamma Interferon test has been used in GB alongside the skin test in certain circumstances to help identify animals at an earlier stage of infection. The tuberculin skin test The tuberculin skin test is the internationally accepted standard for detection of infection with M. bovis, and is considered the best test currently available.

It is designed to test the animal’s immune response and involves injecting a small amount of tuberculin (a harmless protein extract of M. bovis) into the skin of the animal. In most cattle infected with M. bovis, this will cause the animal's immune system to react to the tuberculin and cause a localised allergic reaction (swelling) of the skin a few days after the injection.

Cattle are sometimes infected with other types of mycobacteria which may cause the

animal to react to the test. In order to distinguish between animals infected with M. bovis and those infected by other mycobacterium, each animal is also injected with an extract from the organism that can cause TB in birds (avian TB). The size and nature of the reaction to both tuberculins (‘avian’ and ‘bovine’) are compared to determine whether the test result is considered positive, negative or inconclusive.

The person carrying out your test will be an inspector trained by AHVLA to carry out the tuberculin skin test. This will either be your own veterinary surgeon, an AHVLA Veterinary Officer or an AHVLA Animal Health Officer.

Source : www.farminguk.com      2014/10/30 09:38

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