Ex vivo Diagnosis of Bovine Tuberculosis in Herds with Different Disease Prevalence and Influence of Paratuberculosis Infection on PPDB and ESAT-6/CFP10 Specificity

C AAGAARD,; M GOVAERTS,; V MEIKLE; J A GUTIERREZ PABELLO; J MCNAIR; P ANDERSEN; F SUÁREZ GÜEMES,; J POLLOCK,; C ESPITIA; A CATALDI.

Wellington, Nueva Zelanda

Simposio; V International Conference in M. bovis, Welligton, Nueva Zelanda; 2009

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Bovine tuberculosis (BTB) is a major animal health problem with zoonotic implications. Current control programs are based on test and slaughter strategies utilizing intradermal tests with tuberculins as antigens. The low specificity and associated operative difficulties of these tests have driven the search for new antigens and diagnostic assays. In this multicenter study we used intradermal test positive and negative animals from herds with different prevalences of BTB to compare an ex vivo IFN-g test employing either tuberculin (PPDB) or ESAT-6+CFP10 as antigens. In low prevalence herds, cross reactivity of PPDB was apparent since up to 60 % of the intradermal test positive animals responded to PPDB but only 16 % to ESAT-6+CFP10. The higher specificity of ESAT-6+CFP10 is also supported by results obtained in two BTB-free herds. One of these herds was infected with Mycobacterium avium sp. paratuberculosis and showed a strong crossreactivity with PPDB and PPDA but not with ESAT-6+CFP10. In high prevalence herds, on the other hand, 65-70 % of the intradermal test-positive animals, also tested positive using the IFN- assay with both antigens (PPDB and ESAT-6+CFP10). However, within the high prevalence group 50 % of the intradermal negative animals were positive in the ex vivo assay using both PPDB and ESAT-6+CFP10. This indicates that the intradermal test can yield a significant number of false negative results. In conclusion, the ESAT-6+CFP10 based IFN-g assay should be the preferred test in low prevalence settings due to its high specificity. In high prevalence situations, the IFN-g assay should be used with PPDB or ESAT-6+CFP10 as an ancillary test to accelerate eradication.