ObjectivesTuberculosis (TB) is the leading infectious disease in the developing world. Delayed-type hypersensitivity skin test diagnoses TB using tuberculin purified protein derivative (PPD), but this test is incapable of distinguishing Mycobacterium tuberculosis (MTB) infection from bacillus Calmette–Guérin (BCG) vaccination or an infection caused by nontuberculous mycobacteria (NTM). This study was performed to evaluate the use of recombinant early secretory antigenic target 6 (rESAT-6), a secretory protein found only in MTB, Mycobacterium bovis, and few other mycobacterial species, as a skin marker for MTB in guinea pigs.MethodsWe prepared recombinant MTB ESAT-6 and evaluated its use as a specific antigen for MTB in guinea pigs.ResultsOur results show that the purified MTB rESAT-6 antigen is capable of inducing a positive reaction only in guinea pigs sensitized to MTB. No such reaction was observed in the animals sensitized to M. bovis, BCG vaccination, or NTM (Mycobacterium avium).ConclusionOur study results confirm that the ESAT-6 antigen is more specific to MTB infection than PPD and could be used in more specific skin tests for detection of MTB in large animals and in humans.

Paratuberculosis is an important disease of ruminants with a worldwide distribution. In developing countries where funding constraints challenge establishment of control schemes, large losses are incurred on cattle farmers due to paratuberculosis. In this study, faecal specimens from Holstein-Friesian cows with progressed and moderate clinical paratuberculosis (N = 223) from 13 dairy farms in Isfahan, Central Iran, were subjected to bacterial culture. Culture growth diagnostic for M. avium subsp. paratuberculosis was found in cattle from nine of the 13 farms and in 71 of the cattle studied. These results illustrate the emergence of PTb in this region, and they imply that PTb should be given a higher priority for veterinary measures.

The genus Mycobacterium comprises a broad spectrum of obligate microorganisms most notably the M. tuberculosis complex bacteria; potentially-pathogenic or opportunistic species gathered under the common name of M. avium-intracellulare complex, and finally saprophytic mycobacteria. In cattle farming, Mycobacterium bovis (M. bovis) is considered as the principle cause for bovine tuberculosis (bTB). Nevertheless, non-tuberculosis mycobacteria (NTM) are potential pathogens that are increasingly reported to interfere with contemporary intradermal tuberculin tests in veterinary medicine. Therefore, these neglected mycobacteria are capable to make hurdles for bTB diagnosis. In the Iranian environment, the extent and importance of this phenomenon in regard with the public health and economical aspects is just underestimated. This work was therefore intended to isolate and characterize the mycobacterial organisms potentially involved in causing positive reactions in tuberculination of Iranian cattle. Abattoir meat inspection and laboratory microbiological investigation of slaughtered heifers from a 2,000-head Simental cattle farm with 10% of the herd positive tuberculin reactors, failed to provide any evidence of M. bovis infection. No mycobacteria was detected in bacterial culture of specimens from feedstuff, water or even the visiting feral rodents of the farm. When the farm workers were included in assessments, 22 individuals were found tuberculin-positive with 5 of them also smear-positive in their sputa assessment. Molecular identification of the five isolates from workers through sequencing of the 16SrRNA proved their identity as Mycobacterium thermoresistibile (Mth). Removing of the carrier workers from the farm vicinity, successfully ended the issue of the constantly-positive tuberculin test in the herd with no return of the problem until now. We are convinced further investigations are essential in search for interference extent and importance of NTM species in cattle tuberculination scheme in Iran.