RESUMO
A real-time PCR assay for the measurement of gamma interferon (IFN-gamma) mRNA in European badger (Meles meles) blood cultures was developed. The levels of IFN-gamma mRNA in blood cultures stimulated with either bovine or avian tuberculin or specific mycobacterial antigens were compared with those in a nonstimulated control blood culture as the basis for determining the tuberculosis (TB) status of live badgers. The assay was validated by testing 247 animals for which there were matching data from postmortem examination and culture of tissues. Relative changes in the levels of IFN-gamma mRNA in response to bovine tuberculin and specific antigens were found to be greater among badgers with tissues positive for TB on culture. The test was at its most accurate (87% of test results were correct) by using blood cultures containing bovine tuberculin as the antigen and when the response to avian tuberculin was taken into account by subtracting the avian tuberculin response from the bovine tuberculin response. At a specificity of 90.7%, the test was 70.6% sensitive. At the same specificity, the current serological enzyme-linked immunosorbent assay for TB in badgers was only 53% sensitive. This work demonstrates that measurement of IFN-gamma mRNA by real-time PCR is a valid method for the detection of TB in live badgers and may provide an alternative to the current serological methods of diagnosis, the Brock test. The testing procedure can be completed within 5 h of receipt of the blood culture samples. In addition, the use of a molecular biology-based test offers the potential to fully automate the testing procedure through the use of robotics.
