Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2010
Publication Date: 7/5/2011
Citation: Schiller, I., Waters, W.R., Vordermeier, H.M., Thomas, J., Welsh, M., Keck, N., Whelan, A., Gormley, E., Boschiroli, M.L., Moyen, J.L., Vela, C., Cagiola, M., Buddle, B.M., Palmer, M.V., Thacker, T.C., Oesch, B. 2011. Bovine tuberculosis in Europe from the perspective of an officially tuberculosis free country: Trade, surveillance, and diagnostics. Veterinary Microbiology. 151(1-2):153-159. Interpretive Summary: Despite highly successful eradication efforts in several countries, tuberculosis of cattle remains a serious health concern worldwide. The United States is considering bold new changes to the bovine tuberculosis eradication program. Changes being considered include enhanced testing at borders, switch from a state to zone status, and enhanced mitigation efforts with wildlife reservoirs. This review article provides an overview of current and emerging bovine tuberculosis testing strategies/tools and a vision for incorporation of emerging technologies into the current control/eradication programs. Knowledge presented in this article will be useful for the dissemination of information critical for the advancement of new strategies to be used in the United States tuberculosis eradication program.
Technical Abstract: Switzerland is officially free of bovine tuberculosis (OTF) since 1960. A mandatory eradication program had been launched in 1950. Since 1980 the control of bovine tuberculosis (bTB) has been reduced to passive abattoir surveillance. Single cases of bTB, partly due to reactivation of human Mycobacterium bovis infections with subsequent transmission to cattle, have been noticed in the last years. In Europe, the overall prevalence of bTB is slightly increasing. In 2007, 0.53% of cattle herds were bTB positive compared to 0.48% in 2006. Both OTF and non-OTF countries report increases of the proportion of bTB positive cattle herds. Current bTB eradication and control programs in Europe are facing a range of challenges. Wildlife reservoirs both in non-OTF and OTF countries are responsible for re-infections of and spillover to livestock. Whole herd depopulation is becoming less an option due to economic reasons and due to animal welfare concerns. Live animal trade is increasing both at national and international levels. Regarding these tendencies and taking into account chronicity of bTB disease, pre-movement testing is becoming increasingly important as a central tool for eradication and for protection against re-introduction of bTB. Pre-movement testing, however, specifically focuses on the infection status in individuals, requiring a high level of reliability to correctly diagnose infected animals. Current screening tests for bTB, however, have been designed to meet demands as herd tests. This illustrates that the modification of existing and/or the development of new diagnostics for bTB might be needed. Tuberculin skin test (TST), the primary screening test for bTB may have low sensitivity, as indicated by recent studies: in Northern Ireland only 59% and in a particular region in France (Camargue) only 10.6% of animals with confirmed M. bovis infection were detected by comparative cervical and by single cervical tests. This illustrates that trade is linked with a certain risk to re-introduce bTB in OTF regions or countries. The interferon gamma (IFN-') assay is accepted to be more sensitive compared to TST. Reduced specificity, however, especially in areas of low bTB prevalence, raises concerns. New antigen combinations including Rv3615c, OmpATb and others have been shown to complement ESAT-6 and CFP-10 in the whole blood IFN-' assay and resulted in improved sensitivity (compared to ESAT-6 and CFP-10) and specificity (compared to tuberculins). Lesion detection, the screening test used for active and passive surveillance of bTB, exhibits low sensitivity, as lesions may be localized. A recent study indicates a sensitivity of 28.5% for slaughter surveillance followed by culture. This demonstrates that there may be delays in noticing a re-introduction of bTB in OTF regions or countries. In conclusion, regarding the fact that some parameters linked with bTB programs are changing, the development of improved diagnostic tests with a high reliability for use as individual animal tests will be important for future eradication of bTB, in line with international commitment to high standard animal health programs.