Aim: The aim of this study was to investigate the incidence of bovine tuberculosis (BTB), an old chronic disease having zoonotic potential, covering four districts in Gangetic delta region of West Bengal, India, and to find the prevalence in organized as well as backyard herds and variation in relation to their age, sex, and breeds.

Materials and Methods: The incidence of BTB in exotic and indigenous breeds of cattle (n=173) of various age groups was investigated employing tuberculin (single intradermal tuberculin and comparative cervical tuberculin) tests and gamma interferon assay. Further, milk samples (n=96) from milching animals and antemortem (n=519) samples (nasal swab, buccal swab, and aspirates from pre-scapular lymph nodes) were also screened employing bacteriological and molecular techniques.

Results: In total, 36 (25.4%) animals from organized and one (3.2%) from backyard farming sector were found positive to BTB. Polymerase chain reaction (PCR) of milk samples based on 16S rRNA amplified the 1030 bp band in four samples indicating them belonging to genus Mycobacterium. Species-specific primers used to differentiate between Mycobacterium bovis and M. tuberculosis confirmed the presence of M. bovis. Prevalence of BTB in exotic crossbred animals (34.6%) was significantly higher (p<0.001) compared to indigenous cattle (10.5%). Further, gender-wise analysis of data with respect to BTB revealed higher positivity (p<0.05) among cows/heifers (25.8%) compared to bulls/bullocks (7.3%). Although BTB-positive cattle were detected in all the age groups, no statistical difference (p=0.779) was found among them.

Conclusion: The findings indicate a higher prevalence of BTB in exotic crossbred animals in Gangetic delta and variation in breed susceptibility, thereby suggesting an urgent review of the present policy on adopting national crossbreeding program and implementation of "One Health" approach.

Keywords: bovine tuberculosis, cattle, India, prevalence, West Bengal.

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