Dr. Damien Barrett:

I will start on the Senator's point about animals without lesions, the test sensitivity and specificity and why we do not do wide-scale blood tests. The specificity of the skin test is 99.5%, which means there is one in 5,000 false positives. The fact an animal shows up and lesions are not detected is good news because it means the animal was detected before the lesions had a chance to develop. Lesions are at the end stage of the disease and they are not a good sign. It gives people confidence that it really was TB but in reality a test where there are no lesions, or a minimal number of them, is a better outcome than many lesions.