Evaluation of the tuberculin test in Malawi

In a trial involving 371 head of cattle, the results of using avian plus bovine tuberculin and avian plus mammaliam tuberculin were compared. One group of 185 cattle from areas of low tuberculosis incidence and another group of 186 cattle from areas of high incidence were tuberculin tested and examined for pathological lesions. Using the interpretation "non-specific infection not established" with avian plus mammaliam tuberculin on the readings from cattle from high incidence areas, the test detected 83% of the cattle with visible lesions, whereas the avian plus bovine tuberculin test only detected 63%. The avian plus mammaliam tuberculin test is therefore more accurate; however, it appears to be too sensitive as it produces a higher rate of inconclusive results from non-infected cattle, and is thus more difficult to interpret. Many cattle giving positive reactions were found to be free of tubercular lesions when examined post mortem; the possibility is discussed of their allergy to the test being caused by mycobacteria other than tuberculosis, as mycobacteria belonging to Runyons Group IV have been isolated from some of these cases.