Low Mycobacterium avium subspecies paratuberculosis ELISA Specificity in a Dairy Herd

Johne's Disease (JD) is an important infectious disease of cattle caused by Mycobacterium avium subspecies paratuberculosis (MAP). It is estimated that over 50% of US dairy herds are infected with MAP. Current JD diagnostic tests detect either an immune response to MAP or the actual organism in feces or tissues. The JD ELISA detects antibodies to MAP and is the most common assay used to detect an MAP immune response. Because of the pathogenesis of JD, the sensitivity of the JD ELISA is reported to be less than 50% when used to detect JD infected adult cattle. The specificity of the JD ELISA is reported to be greater than 90%. However, the assay specificity may vary significantly between herds. In this case study, low MAP ELISA specificity in an individual dairy herd is described.