Presentation on theme: "A Review of Aspects of the Epidemiology of TB in the Irish Cattle Herd 1 Department of Agriculture and Food,Agriculture House, Kildare Street, Dublin,"— Presentation transcript:
A Review of Aspects of the Epidemiology of TB in the Irish Cattle Herd 1 Department of Agriculture and Food,Agriculture House, Kildare Street, Dublin, 2, Ireland. 2 Centre for Veterinary Epidemiology and Risk Analysis, Faculty of Veterinary Medicine, University College Dublin, D4, Ireland. James O’Keeffe 1 and Paul White 2 Background The single intradermal comparative tuberculin test (SICTT) is used as the screening test for tuberculosis on the 7 million cattle within 130,000 herds in Ireland. Where animal(s) react positively to the SICCT, the herd is restricted from trade and all such reactor animals are removed for slaughter where they undergo a routine post-mortem examination. A TB episode is defined as the interval from when a herd’s EU trading status is removed because Tuberculosis is either suspected or confirmed, to when the herd again qualifies to trade. Episodes are classified into 6 groups based on Standard Reactors and Lesions identified. The definitions of the 6 classes were chosen to broadly reflect the current EU definitions of confirmed and unconfirmed tuberculosis. The classification system is a useful way to qualitatively describe tuberculosis breakdowns in a National population over a number of years. The parameters that define episode groupings and the overall number and percentage of episodes in each group for the period 1989 to 2002 are set out in Table 1. Group 1 episodes are further subdivided in Table 2. Results A total of 137,763 TB episodes occurred over the years 1989 to 2002. Group 6 episodes include herds with the least evidence of TB, and are often associated with the finding of a confirmed lesion in non-reactor animal at slaughter. The Irish experience regarding factory lesions shows that the majority are negative at subsequent TB tests. Groups 2 and 5 include single standard reactor breakdown (singleton) episodes. Further analysis of singleton episodes indicate that the presence of a lesion is not associated with increased risk of future breakdown, compared with episodes with no lesion identified 1. Groups 3 and 4 include potential instances of false negative and false positive test outcomes respectively. Detailed epidemiological investigations are routinely carried out on Group 1 episodes in herds. These investigations are carried out by State Veterinarians using a standardised reporting format (ER76). The outcome of 1,466 investigations are shown in Tables 3,5,6,7 and 8 and include both objective and subjective assessments of the likely sources of infection. For objective assessment, a weighting system (Table 4) is employed for each likely source. References References Olea-Popelka F.J., White P.W., Collins J.D., O’Keeffe J. Kelton D.F., Martin S.W. (2004). Breakdown severity during a bovine tuberculosis episode as a predictor of future herd breakdowns in Ireland. Preventive Veterinary Medicine 63: 163-172. Table 5. Weights for purchasing given that purchasing took place Table 6. Weights for residual infection Table 7. Weights for contiguous infected herds Table 8. Weights for badgers in the environment Conclusion Figures 1, 2 and 3 illustrate the weightings for alternative sources for herds where a contiguous source is least possible (i.e. weighting 1, 2 or 3). A common finding of Irish investigators is that multiple sources are possible, the most common being contiguous, residual and badgers. Figure 1. Figure 2. Figure 3. Table 2. Group 1 Episodes Table 1. TB Episode Classification Table 3: Subjective Assessment of Source of Infection Table 4: Objective Weightings
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