[Establishment and evaluation of an ELISA for the detection of antibodies in milk against Mycobacterium avium subspecies paratuberculosis]. / Etablierung und Evaluation eines ELISA zum Nachweis von Antikörpern gegen Mycobacterium avium subspecies paratuberculosis in Milch.

ABSTRACT

Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) is the etiological agent of paratuberculosis (Johne's Disease), a chronic granulomatous enteritis of ruminants occurring worldwide with increasing frequency and leading to growing economic losses. Continuous surveillance of dairy farms would be advisable, particularly with respect to the increasing economic importance of paratuberculosis and the high tenacity of the pathogen, which can persist in the environment for many months. So far, such measures have not been taken as the cost-intensive collection of serum samples would have been required. Based on these considerations, it was the aim of this study to evaluate an economically viable diagnostic method for antibody detection using milk samples. This objective was reached by establishing a milk-ELISA. A commercially available test (Svanovir-ELISA by Svanova, Sweden) was chosen, because this ELISA has an excellent specificity with respect to cultural examination of the ileocaecal lymph node ("Gold-Standard"). The Svanovir-ELISA could be successfully adapted for testing milk for antibodies against M. paratuberculosis. The milk is skimmed by centrifugation and is diluted 110 for testing. The inter-assay-variation was 17%. A comparative antibody analysis done in parallel with milk and serum samples from 601 dairy cows using the Svanovir-ELISA showed a significant correlation between the results obtained with both methods. The optimal "cut-off" for the milk-ELISA of 46 EUMS (> 46 EUMS = positive) resulting in a specificity of 94.6% and a sensitivity of 60.9% was confirmed by receiver-operator characteristics (ROC) analysis. In the meantime the Svanovir-ELISA has been licensed for use with milk samples in Germany.