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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVED TB TEST FOR CATTLE

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Title: Bovine Tuberculosis in Europe From the Perspective of an OTF Country: Trade, Surveillance and Diagnostics)

Author
item Schiller, Irene
item Waters, Wade
item Vordermeier, H
item Jemmi, Thomas
item Welsh, Michael
item Keck, Nicolas
item Whelan, Adam
item Gormley, Eamonn
item Boschiroli, Maria
item Moyen, Jean
item Vela, Carmen
item Cagiola, Monica
item Buddle, Bryce
item Palmer, Mitchell
item Thacker, Tyler
item Oesch, Bruno

Submitted to: Meeting Abstract
Publication Type: Abstract only
Publication Acceptance Date: 8/25/2009
Publication Date: 8/25/2009
Citation: Schiller, I., Waters, W.R., Vordermeier, H.M., Jemmi, T., Welsh, M., Keck, N., Whelan, A., Gormley, E., Boschiroli, M.L., Moyen, J.L., Vela, C., Cagiola, M., Buddle, B., Palmer, M.V., Thacker, T.C., Oesch, B. 2009. Bovine Tuberculosis in Europe From the Perspective of an OTF Country: Trade, Surveillance and Diagnostics [abstract].

Interpretive Summary:

Technical Abstract: Switzerland is officially free of bovine tuberculosis (OTF) since 1960. A mandatory eradication program had been launched in 1950, herd prevalence at that time accounted for 25%. 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 (M.) bovis infections with subsequent transmission to cattle, have been noticed in the last years. In Europe, the overall prevalence of bTB is currently 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. Eradication in high prevalence countries like the United Kingdom is expected to take at least 20 years. Wildlife reservoirs both in non-OTF and OTF countries are responsible for reinfections 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. Trade underlies more and more concepts like regionalization, zoning and compartimentalisation. 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 reintroduction of bTB. Pre-movement testing, however specifically focuses on the infection status in individuals. This illustrates that requirements for diagnostic tests have changed. A high level of reliability to correctly diagnose infected animals is needed. 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 required. In this presentation we address these issues by summarizing published data on diagnostic tests for bTB in addition with new data. The tuberculin skin test (TST) constitutes the primary screening test for bTB, either as caudal fold test (CFT), as single cervical intradermal test (CIT) or as comparative cervical test (CCT). Summary of data from international studies indicate 68-96.8% sensitivity and 96-98.8% specificity for CFT, 80-91% sensitivity and 75.5-96.8% specificity for CIT, 55.1-93.5% sensitivity and 88.8-100% specificity for CCT. Recent data from Northern Ireland and a particular region in France (Camargue) indicate a markedly reduced sensitivity of TST: only 59% (CCT, Northern Ireland) respectively 10.6% (CIT, Camargue) of animals with confirmed M. bovis infection were detected. The interferon gamma (IFN-gamma) assay is used complementary to TST as screening test for bTB. Sensitivity and specificity of the IFN-gamma assay estimated in international studies range from 73.0 to 100% and from 85.0 to 99.6%. The IFN-gamma assay is accepted to be more sensitive compared to skin test. Follow-up studies of TST-negative cattle showed that IFN-gamma positive cattle were at an Odd ratio (OR) of 8.9 to become a TST-reactor at the next testing occasion, respectively IFN-' positive cattle had an 18% risk of reacting TST-positive within one year. In France (Camargue), the IFN-' assay achieved a herd and animal sensitivity of 96 and 66.2%, compared to CCT with only 58 respectively 10.6%. Reduced specificity of the IFN-' assay, however, especially in areas of low bTB prevalence rises concerns. Delayed initiation of culture in a PPD-based assay (24h compared to 8h after blood collection) resulted in a significant improvement of specificity (97% compared to 85%), whereas there was only a modest reduction of sensitivity (from 96% to 90%), which was statistically not significant. Still, the replacement of tube

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