Ante-mortem diagnosis of caprine tuberculosis in persistently infected herds: Influence of lesion type on the sensitivity of diagnostic tests

Caprine tuberculosis is a major health problem for goats, and an important zoonosis. Eradication programmes using the comparative skin test are being developed to aid in decreasing the prevalence of infection. However, persistent tuberculosis infections are found in herds subjected to eradication programmes. In the present study a commercial IFN-γ release assay and an experimental ELISA based on MPB70, were evaluated as potential ancillary tests to detect infection. The relationship between the three techniques (skin test, IFN-γ release and ELISA) and histopathological lesions was analyzed in 162 goats from herds with persistent tuberculosis infection. The presence of related pathogens (paratuberculosis and pseudotuberculosis) was also studied. The IFN-γ release assay and the ELISA had a higher sensitivity than the comparative skin test (65.3% and 66.3% vs 44.5%) using as a gold standard a combination of histopathological analysis and isolation. Used in combination, ELISA and the skin test detected 89.1% of goats with tuberculosis while a combination of IFN-γ assay and skin test detected 78.2%. The types of macroscopic and microscopic lesions reflected the results of diagnostic tests.