Development of an ELISA technique for serodiagnosis of bovine paratuberculosis.

A local clinical Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) isolate was cultivated in large-scale culture. A procedure for efficient preparation of a lipoarabinomannan-containing antigen was developed and standardized; 25 mg of purified antigen were obtained per gram of bacterial wet weight. An ELISA based on this antigen was developed. Intra- and interassay variation were determined to be 20% and 27%, respectively. The ELISA was evaluated using the sera of groups of 39 non-randomly selected and 92 randomly selected animals from which ileocaecal lymph nodes were cultured to isolate viable M. paratuberculosis. Combining the results of both groups a positive predictive value of 74% and a negative predictive value of 99% were calculated. The ELISA was licensed by the German regulatory agencies and, in a direct comparison, was found to be superior to both other licensed assays.