Infections with Mycobacterium avium subsp. paratuberculosis(MAP) can be latent for years without affecting the animal, but the infection may result in the animal becoming infectious and developing clinical disease. Diagnosis can be a challenge primarily in latent stages of the infection, and because different decision makers have different target conditions for a diagnosis. The objective of this study was to provide a critical review of reported accuracies of ELISA and faecal culture (FC) tests used for diagnosis of three defined target conditions in cattle: MAP infected, MAP infectious and MAP affected animals.

For each target condition and test, sensitivities (Se) and specificities (Sp) were summarised. The diagnostic test information varied substantially for tests of the same type and make, particularly ELISA. For affected and infectious animals, the Sp of FC was set to 1.0 by definition. Se reported for FC in infectious and affected cattle were 0.74 and 0.70, respectively, whereas Se for infected cattle were 0.23 to 0.29. Se for ELISA were in the ranges 0.50 to 0.87 for affected, 0.24 to 0.94 for infectious and 0.07 to 0.39 for infected cattle, but Se of ELISA should always be interpreted with Sp, which also varied considerably.

The variation in reported Se and Sp may primarily be a reflection of the choices of the test-evaluators regarding weighing of either Se or Sp, study design and population. Comparison of the various tests accuracies was generally not possible, but stratification of test-evaluations by target condition improved the interpretation of the test accuracies. Infectious and affected animals can often be detected, but Se for infected cattle is generally low. A main conclusion of the review was that the quality of design, implementation and reporting of evaluations of tests for paratuberculosis was generally poor. Particularly, there is a need for better correspondence between the study population and target population, i.e. the subjects chosen for test evaluation should reflect the distribution of animals in the population, where the test is intended to be used.