Evaluation of Relative Potency of Human Tuberculin Skin Test in the Guinea Pigs Sensitized with Mycobacterium Tuberculosis, M. Bovis BCG and M. Avium

The tuberculin skin test is the most commonly used test for diagnosing tuberculosis (TB) infection. The basis of tuberculin testing is the induction of a delayed hypersensitivity reaction to the intradermal injection of tuberculin. Unfortunately, this test is incapable of distinguishing Mycobacterium tuberculosis infection from Bacille Calmette-Guerin (BCG) vaccination or infection with non-tuberculous mycobacteria. The aim of this study is to evaluate the relative potency of human tuberculin skin test) produced by Razi Vaccine and Serum Research Institute (in the guinea pigs sensitized with M. tuberculosis, M. bovis BCG and M. avium. For skin test, different groups of guinea pigs were sensitized with M. tuberculosis, M. avium and M. bovis BCG. Guinea pigs were injected intradermally with 0.1 ml of 0.4, 2 and 10 µg/ml of tuberculin. Skin reactions (diameters of erythema, in millimeters) were independently measured 24 h after injection and results were calculated. The results showed that the specificity index of human tuberculin test for guinea pigs sensitized with M. bovis BCG in compare of guinea pigs sensitized with M. tuberculosis was equal and for guinea pigs sensitized with M. avium was not equal. This study demonstrated that human tuberculin test produced by Razi Institute for diagnosis of latent infection to M. tuberculosis has lower specificity for M. bovis in comparison with M. avium.