With the every increasing number of cattle with the disease the threat to humans is increasing. The disease can be spread through contaminated raw milk or interfaces such as open woulds and breathing in the bacterium through the mouth or nose. Because can infect people through raw milk, dairy farmers and their families are at very high risk as they tend to drink the milk straight from the tank. In cattle it causes weight loss and coughing and sometimes diarrhea if it affects the digestive system. In humans the secondary infection causes lung damage, can spread to other parts of the body and be fatal.
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| One of the calves at the dairy placement |
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| Measuring skin flap with callipers |
I was lucky enough to observe a TB test whilst on my mixed veterinary placement.
On the first visit the vet injects an avian and bovine strain of TB into the neck next to each other in the same place on each cow, for example bovine on left and avian on right (not sure if this is the correct way round but this is an example) and measures with calipers the diameter of the flap of skill surrounding the injection. After two days the vet returns and measures the swelling around the injections. The bigger the swelling, the larger the reaction. Therefore, if the bovine strain swells up more than the avian strain the animal is suspected to have TB. If the farm is in a high risk TB area then it is tested every year, if low risk then tested every 4 years. As another measure at the abattoir they look in the lungs for TB nodules to prevent TB infected animals entering the food chain. If their is a suspected case of TB, all farms within 3km are investigated.
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| TB nodules in the lung of a deer |
Further reading: I would recommend this for further reading as I found it very interesting.
http://www.bovinetb.info/testing.php
References BVA,
