Evaluation of Surveillance for Documentation of Freedom from Bovine Tuberculosis
Abstract
:1. Introduction
- (1)
- to evaluate the sensitivity of each of the surveillance system components given that bTB would enter one of these components, but not necessarily spread between these due to limited contact and risk of transmission between the four components;
- (2)
- to estimate the probability of freedom from bTB in Denmark over time, and
- (3)
- to evaluate how future alternative programmes based on visual meat inspection and risk-based meat inspection would affect the probabilities of freedom from bTB compared to the current meat inspection system, at the very low animal-level design prevalence 0.0002% and a low probability of introduction of 1% and 0.1%.
2. Results and Discussion
2.1. Results
Surveillance programme/SSC | Design prevalence | Units processed | CSe (95% CI) |
---|---|---|---|
a Average number of cattle slaughtered between January 2004 to June 2012 in Denmark; b Alternative surveillance programmes were not investigated for these SSCs. | |||
Current surveillance system (Invasive in all slaughtered animals) | |||
Domestic cattle | 0.000002 | 498,364a | 0.32 (0.28–0.36) |
Pig | 0.000002 | 20,022,790 | 0.68 (0.52–0.80) |
Deerb | 0.000125 | 8,000 | 0.43 (0.31–0.53) |
Export cattleb | 0.00038 | 2,634 | 0.07 (0.05–0.09) |
Alternative scenario 1 (100% visual inspection cattle) | |||
Domestic cattle | 0.000002 | 498,364 | 0.18 (0.15–0.20) |
Alternative scenario 2 (100% visual inspection pigs) | |||
Pig | 0.000002 | 20,022,790 | 0.43 (0.30–0.54) |
2.2. Discussion
3. Methods
3.1. Scenario Tree
3.2. Population and Risk Category Node
Input variable | Input value and distribution | Source | |
---|---|---|---|
Design prevalence (PA) for domestic cattle and pigs | 0.000002 | Adjusted from [3] | |
Design prevalence (PA) for deer | 0.000125 | Calculated: 1 animal out of 8000 | |
Design prevalence (PA) for exported cattle | 0.00038 | Calculated: 1 animal out of 2634 | |
Proportion of young and adult animals per SSC (PropUG) | |||
Domestic cattle | Young | 0.3 | Danish Cattle Database (DCD) |
Adult | 0.7 | ||
Pig | Young | 0.98 | Danish Agriculture & Food Council |
Adult | 0.02 | ||
Deer | Young | 0.9 | Danish Agriculture & Food Council |
Adult | 0.1 | ||
Export cattle | Young | 0.77 | Danish Knowledge Centre of Agriculture, Cattle |
Adult | 0.23 | ||
Relative risk of infection between the young and adult groups (RR) | RiskPert (1.5, 2, 3) | [7] | |
Proportion of lesions present (PropL) | |||
Adult animals | RiskBeta (84, 58) | [21] | |
Young animals | 50% of adults | ||
Proportion of lesions detected (PropD) | |||
Current programme | RiskPert (0.9, 0.95, 0.99) | [7] | |
Alternative programme | 50% of the current | ||
Proportion of lesions submitted (PropS) | |||
Pig SSC | RiskPert (0.005, 0.1, 0.15) | Expert opinion | |
Other three SSC | RiskPert (0.7, 0.8, 0.9) | [7] | |
Meat inspection Se (PropD) | RiskPert (0.29, 0.6, 0.86) | [9,21,22,23,24] | |
Bacteriological culture test Se (TestSe) | RiskPert (0.92, 0.95, 0.98) | [7] | |
Intradermal tuberculin test Se (TestSe) | RiskPert (0.53, 0.7, 0.96) | [25] | |
Probability of introduction (PIntro) | 0.001 and 0.01 | Evaluation of import practices |
3.3. Population and Risk Category Node
3.4. Detection Nodes
- (1)
- The proportion of lesions present (i.e., granulomas) in the animals. This was set 50% lower for young animals than adult animals, and was modeled using a beta distribution based on an efficiency study of inspection procedures for detection of tuberculous lesions in cattle [21];
- (2)
- The proportion of granulomas detected at meat inspection, modeled using a pert distribution based on [7];
- (2)
- The proportion of granulomas submitted for confirmation by bacterial culture. Based on expert opinion, the proportions were set higher for domestic cattle than for pigs (Table 1), because around 90% of tuberculous lesions found in pigs are detected in the gastro-intestinal tract and according to the current meat inspection legislation, these lesions will not be submitted for confirmatory bacterial culture, as they are in the cattle abattoirs [26]. The last detection node for domestic cattle and pigs SSCs was the probability of testing positive at culture, modeled using a pert distribution (Table 2) [7].
3.5. Component and Overall System Sensitivity Calculations
3.6. Probability of Freedom
3.7. Simulations
3.8. Modeling of Alternative Surveillance Systems Based on Visual Inspection
4. Conclusions
Acknowledgments
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Calvo-Artavia, F.F.; Alban, L.; Nielsen, L.R. Evaluation of Surveillance for Documentation of Freedom from Bovine Tuberculosis. Agriculture 2013, 3, 310-326. https://doi.org/10.3390/agriculture3030310
Calvo-Artavia FF, Alban L, Nielsen LR. Evaluation of Surveillance for Documentation of Freedom from Bovine Tuberculosis. Agriculture. 2013; 3(3):310-326. https://doi.org/10.3390/agriculture3030310
Chicago/Turabian StyleCalvo-Artavia, Francisco Fernando, Lis Alban, and Liza R. Nielsen. 2013. "Evaluation of Surveillance for Documentation of Freedom from Bovine Tuberculosis" Agriculture 3, no. 3: 310-326. https://doi.org/10.3390/agriculture3030310