Comparison of avidin-biotin complex (ABC) and ZN techniques for detection of Mycobacterium avium subspecies paratuberculosis in natural and experimental paratuberculosis in sheep

The present investigation was carried with the objective to study the diagnostic efficacy of Avidin-biotin complex (ABC) staining technique in detection of Mycobacterium avium subspecies paratuberculosis (MAP) and its antigen. ABC staining technique was performed on 14 (6 multibacillary, 8 paucibacillary) naturally occurring slaughterhouse and 16 archived experimental samples showing lesions suggestive of paratuberculosis (Johne's disease) for demonstration of MAP and its antigen in sheep. In natural cases, 11 (78.57%) were positive, of which six had demonstrable acid-fast bacilli (multibacillary) and 5 (62.5%) had either rare or no bacilli. Of 16 archived samples of sheep, 12 (75%) showed positive immunoreactions, which included all 10 (100%) cases with demonstrable acid-fast bacilli and 2 (33.33%) of 6 sheep with non-demonstrable acid-fast bacilli. Sensitivity of ABC technique was found to be 78.57% and 75% against ZN staining (71.4% and 62.5%) in naturally occurring slaughterhouse and experimental archived tissues. The study suggested that ABC technique was more sensitive in detection of MAP and its antigen than ZN technique, which detects acid-fast bacilli.