Serodiagnosis of Mycobacterium bovis infection in badgers: development of an indirect ELISA using a 25 kDa antigen.

A 25 kDa antigen of Mycobacterium bovis has previously been identified as immunodominant during badger infections. This 25 kDa antigen was partially purified from sonicated M bovis bacilli by using water precipitation and ion exchange chromatography, and its purification was monitored with a mouse monoclonal antibody, MBS43, which was specific for the antigen. The partly purified antigen was used to develop an ELISA for the assay of badger sera for the presence of specific antibodies. A presumed negative badger population was used to calculate the assay's threshold of seropositivity and using this value, its sensitivity (37 percent) and specificity (98 percent) were determined in a second population of known culture status. The results indicate that it may be possible to develop a specific and cost effective serological field assay for the diagnosis of M bovis infection in living badgers.