Immunodiagnosis

Immunodiagnostic tests such as ELISA, AGID, intradermal skin testing, lymphocyte transformation and IFN-γ assays generally have poor diagnostic sensitivity and can be significantly affected by the stage of infection (Gumber et al., 2006).

The sensitivity of the antibody ELISA to detect MAP infection appears to depend on the type of kit used. One study of the Parachek™ ELISA reported a sensitivity of 16% at a specificity of 9 7.5% (Robbe-Austerman et al., 2006a). Another antibody ELISA (Institut Pourquier, now Idexx) had a sensitivity of 34.9% and a specificity of 98.8% (Gumber et al., 2006). The AGID has been found to have an even lower sensitivity than the ELISA (Gumber et al., 2006; Robbe-Austerman et al., 2006a). Again, the sensitivity of the IFN-γ assay is low, ranging from 40-75% with specificities ranging from 88-98% (Stewart et al., 2002; Robbe-Austerman et al., 2006b). The sensitivities of the intradermal skin test and the lymphocyte proliferation (or transformation) assays have not been examined in detail, with different studies using various cutoff points for diagnosis of infection (Williams et al., 1985; Reddacliff and Whittington, 2003; Robbe-Austerman et al., 2006a). Validation of the diagnostic assays by defining specificity and sensitivity against the gold standard tests of tissue or faecal culture/PCR is becoming more common. If validation of the assays is not done, then researchers and clinicians are left with a poor understanding of the assay's operating parameters and how they can use them under different circumstances to diagnose disease.

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Source: Behr Marcel A., Stevenson K., Kapur V. (eds.). Paratuberculosis: Organism, Disease, Control. 2nd edition. — CAB International,2020. — 439 p.. 2020

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Immunodiagnosis

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