Why is TB diagnosis difficult?
Most of the modern disease diagnosis and surveillance have been based on detection of antibodies: looking for the body’s response to a disease agent, rather than the disease agent itself. Animals develop antibodies in response to foreign proteins. In most diseases, the antibodies give a reliable indication of infection with a disease agent. However the TB pathogen is one of a group of more insidious disease agents. Few antibodies are produced until late in infection when the pathogen is well established and clinical signs of disease are already apparent. What the test tells you in live animals is that those animals have been exposed, and are infected with the bacterium that causes Tuberculosis. It is important to realize that all animals that are infected, do not necessarily develop the disease, and do not necessarily eventually die as a consequence of Tuberculosis. They do not know at this stage what proportion of the animals are infected with the disease and how many will eventually