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Abstract
Diagnosis of tuberculosis in animals in Egypt up till now is still under taken by the single intradermal cervical tuberculin test by using human PPD (prepared from M. tuberculosis). And recently many authors suggest the use of ELISA as a complementary test to the tuberculin test to improve the test specificity and sensitivity .
So the following trials were carried out:
• 1200 dairy cattle from (Monofia, Sharkia and Port Said) Governorates were tested by the single intradermal cervical tuberculin test by using human PPD, 64 animals (5.3%) gave positive results. The positive reactors were slaughtered and the post mortem examination was carried out and it was found that 46 (71.9%) showed visible lesions as follows {4(6.3%) showed generalized tuberculosis, 24 (37.5%) showed pulmonary TB lesion, 12 (18.8%) have extrapulmonary tuberculosis and lastly 6 (9.4%) have mixed TB lesions} while the other 18 animals (28.1%) failed to show any visible lesions.
• The bacteriological examination of the positive reactors cleared that 38 (59.4%) were M. bovis. At the same time MOTT were isolated from 6 animals (9.4%) of them (4) were have extrapulmonary tuberculosis and (2) showed mixed TB lesion. Also 2 (11.1%) M. bovis were isolated from cases with non visible lesions.
The Mycobacterial Growth Indicator Tube (MGIT) system was used to evaluated its ability to detect mycobacteria directly from clinical specimens of positive tuberculin cattle in comparison with the conventional solid culture (Lowenstein–Jensen medium) from the aspect of the recovery rate and the time for detection of mycobacteria from tissue samples.
So, a total of 64 clinical specimens from tuberculin reactive cattle were tested . The recovery rates of mycobacteria were 44 (68.8 %) for MGIT versus 41 (64.1 %) for conventional solid culture. The mean times for detection of mycobacteria were significantly shorter in MGIT 14 (5-37 days) compared to 28 (12–56 days) for conventional solid culture. The results of this preliminary study indicate that MGIT mycobacterial culture system appear to has potential for routine use in mycobacteriology for both high recovery rate and rapid detection of mycobacteria directly from clinical specimens.
It is possible to prepare ST-CF antigen from M. bovis by recent techniques and use it for diagnosis of bovine tuberculosis in comparison with bovine PPD by measuring antibodies using ELISA test on the sera of the positive tuberculin reactor cattle , positive ELISA results were obtained with 43 (93.5%) animals have visible lesions by using ST-CF as coating antigen while by using bovine PPD ELISA positive results were obtained with 42 (91.3%). While the animals that have non visible lesions, positive tuberculin test and 2 (11.1%) M.bovis were isolated from them, positive ELISA results were obtained with 3 (16.7%) animals with ST-CF while by using bovine PPD ELISA positive results were obtained with 4 (22.2%) animals.
The ELISA test showed higher sensitivity and specificity on using ST-CF as coating antigen (93.4%), (83.3%) than in case of using bovine PPD as coating antigen (91.3%) (77.8%).
The positive predictive value of the ELISA test was (93.4%) in case of ST-CF, while it was (91.3%) in case of bovine PPD as coating antigens. Also the negative predictive value was (83.3%),(77.8%) for ST-CF and bovine PPD respectively. And lastly the accuracy index of ELISA test was (90.6%) and (87.5%) for ST-CF and bovine PPD respectively.
It is clear from the preliminary results that using of ST-CF antigen has appreciable value in diagnosis of bovine tuberculosis as it is a useful antigen to minimize non specific reactions in comparison with bovine PPD serologically by measuring antibodies using ELISA .
Also the results of this study indicate that MGIT system appear to has potential for routine use in mycobacteriology for both high recovery rate and rapid detection of mycobacteria directly from clinical specimens.