Bulk-tank milk ELISA antibodies for estimating the prevalence of paratuberculosis in Danish dairy herds

Paratuberculosis (Johne's disease) has been widespread in Danish dairy herd s for a long time but the herd-level prevalence has never been determined p recisely. To evaluate the prevalence of paratuberculosis in Danish dairy he rds in various regions, an ELISA based on a commercially available antigen was adapted for testing bulk-tank milk for the presence of antibodies to My cobacterium avium subsp. paratuberculosis. Bulk-tank milk samples were coll ected from six milk-collecting centres from six different areas of the coun try. Samples from 900 herds (about 7.5% of all Danish dairy herds) were exa mined, and 70% were positive at the statistically optimal cut-off (sensitiv ity 97.1%; specificity 83.3%). The technical performance of the ELISA was n ot sufficient to provide a tool for surveillance because even slight change s in optical density for the samples would change the classification of som e samples. The infection is more widespread than previous investigations ha ve shown. (C) 2000 Elsevier Science B.V. All rights reserved.