Abstract

A cross-sectional study was conducted on 858 cattle (371 recruited from Bako Agricultural Research Center, BARC and 487 from Bako municipal abattoir) from October 2009 to April 2010 to isolate and characterize Mycobacterial species from Skin positive reactors and pathological lesion positive cattle. To this effect, comparative intradermal tuberculin (CIDT) test, post mortem examination, bacteriological culturing, and genus typing using multiplex polymerase chain reaction (PCR) were applied. On the basis of CIDT, prevalence of positive reactors was 1.3% (95% CI: 0.15; 2.45) at the cut-off point of ≥4 mm following the recommendation of the World Organisation for Animal Health (OIE), and 9.0% (95% CI: 6.0; 12.0) following the recently suggested cut-off of >2 mm. Apart from sex (P=0.047), there was no association between host related risk factors and positive reactors upon univariate analysis. However, animals in the age category of 2 to 5 years, those with medium body condition score and cattle born on farm were at high relative risk of infection than the other categories. Lesion positivity in slaughtered cattle was 9.3% (95% CI: 6.3; 11.8). Lesions were more frequent and severe in the mesenteric (60.9%), retropharyngeal (17.4%), and bronchial (17.4%) lymph nodes of slaughtered cattle. Culture positivity in suspicious tissues was 32.6% (29/89) out of which 69% (20 of 29) was confirmed to be acid-fast bacilli (AFB) on Ziehl Neelsen staining. Furthercharacterisation of these isolates using genus typing (multiplex polymerase chain reaction) revealed that all of the isolates were members of the non-tuberculous mycobacteria (NTM). The isolation of NTM from tubercle lesions underlines their roles in causing lesions, which are similar with lesions caused by Mycobacterium bovis. Therefore, further investigations to identify the specific species, the source of infections, transmission route and the pathogencity of NTM in specific host is recommended.

Key words: Bovine tuberculosis, non-tuberculous mycobacteria, grazing cattle, genus typing, Ethiopia.