Detection of infected animals is a key step in eradication programs of tuberculosis. Paratuberculosis infection has been demonstrated to compromise the specificity of the diagnostic tests. However, its effect on their sensitivity has not been clarified. In the present study, skin tests and the interferon-gamma (IFN-γ) assay were evaluated in a goat flock (n = 177) with a mixed tuberculosis-paratuberculosis infection in order to assess the possible effect of paratuberculosis on their sensitivity. Culture of mycobacteria was performed as the gold standard to determine the true infection status. All techniques showed lower sensitivities than previously described; the single intradermal tuberculin (SIT) test and the IFN-γ assay detected 71% (62.4-78.6, 95% C.I.) of the infected animals; the single intradermal cervical comparative tuberculin (SICCT) test detected only 42.7% (34.1-51.7, 95% C.I.) of infected animals. The highest level of sensitivity was obtained when SIT test and IFN-γ assay were combined in parallel (90.8%, 84.5-95.2, 95% C.I.). Sensitivities of the tests were also assessed by comparing animals suffering tuberculosis and animals with a mixed infection; tests were found to be more effective in the former group. Paratuberculosis seems to have a major effect in the sensitivity of the diagnostic tests under study, and therefore must be taken into account; in particular, the use of the SICCT test should be questioned when both tuberculosis and paratuberculosis are present.
Bibliographical noteFunding Information:
This research was funded by project AGL2004-08092 of the Spanish Ministry of Science and Technology, and by ParaTBTools (STREP 23106) of the European Union. J. Álvarez was recipient of a predoctoral grant assigned by the Spanish Ministry of Education and Culture. The group is a partner of the coordination action “Veterinary European Network on Mycobacteria (VENoMYC)” funded by the European Union. We would like to thank C. Escribano, L. Carbajo, J.L. Paramio, (Dirección General de Ganadería, Spanish Ministry of Agriculture Fisheries and Food), L. Sánchez, J. Carpintero, R. Díaz, (Dirección General de Agricultura y Desarrollo Rural, Comunidad de Madrid), and B. Fernández-Mardomingo, O. Mínguez-González, A. Grau and S. Marques (Dirección General de Producción Agropecuaria, Junta de Castilla y León) for their continuous encouragement.
- Skin test