Map is the etiological agent of Johne’s disease (synonym: paratuberculosis). This disease affects several ruminant species. Map multiplies in the intestinal mucosa and induces a progressive enteritis resulting in chronic diarrhea, wasting, drop in milk production and eventually death.
The diagnosis of Johne’s is based on the demonstration of Map in the feces or tissues or of Map specific antibodies in the serum or milk. The most sensitive serological assays to detect Map specific antibodies are enzyme linked immune enzymatic assays (ELISA). The sensitivity of these tests increases with the progression of the infection.
Some animals free from Map have antibodies directed against other environmental mycobacteria that may cause non-specific reactions. Pre-treatment of their sera with selected mycobacteria allows removing these non-specific antibodies.