Towards more accurate diagnosis of bovine tuberculosis using defined antigens

Diagnostic accuracy is of paramount importance in test-and-slaughter progra mmes for the eradication of bovine tuberculosis (TB). Currently applied met hods, such as in vivo skin testing and in vitro interferon-gamma (IFN-gamma ) testing, utilize purified protein derivatives (PPDs), which are poorly-de fined mixtures containing many individual antigenic components. It is known that false-positive responses to these reagents can occur in cattle which are not infected with TB, largely because of that antigenic complexity. Thi s paper reviews recent approaches to the characterization of more precisely defined diagnostic tools which can be used to develop tests with greater s pecificity. For example, the low mass secreted protein ESAT-6 has been show n to be capable of differentiating TB-infected cattle from those which deve lop responsiveness to PPD through contact with environmental mycobacteria o r vaccination with BCG. The information which has accumulated in recent yea rs has shown that the increased specificity is associated with some decreas e in test sensitivity. but the overall advantages of being able to make pre cise diagnostic decisions will have significant advantages in many situatio ns. (C) 2001 Harcourt Publishers Ltd