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Table 2 Main surveillance parameters with current estimates

From: A new bovine tuberculosis model for England and Wales (BoTMEW) to simulate epidemiology, surveillance and control

Parameter definition Symbol Estimate (Range) S-T range Source / Derivation
Maximum probability of detecting one infected animal in a herd test using the SICCT skin test a 0.48
(0.36–0.63)
0.45–0.53 In literature [22, 33] and estimated by fitting. The number of breakdowns disclosed by slaughterhouse surveillance is sensitive to this parameter.
Maximum probability of detecting one infected animal when it is moved from a holding within an area where pre-movement testing is applied. a m 0.32
(0.24–0.42)
N Detection reduced by exemptions from pre-movement testing. The recorded number of pre-movement skin tests was about ½ the number of movements from areas with pre-movement testing. Detection > 0.48/2 because infected cattle were more likely to be in movements without exemptions.
Infection duration until SICCT reaches maximum sensitivity t L 35 (20–200) d N Experimental evidence [20].
Specificity of an individual SICCT skin test. sp Sk 0.9998 N The estimate of Goodchild et al. [34].
Proportion of age class i that is tested in a regular herd test w 1
w2..w5
0
0.5–1.0
0
0.50–0.78
Fitted to observed numbers of regular herd tests.
Frequency of generic herd tests on infected herds g i Location dependent 0.020–0.09 mth−1 Fitted to observed numbers of breakdowns detected by generic herd tests.
Frequency of generic herd tests on uninfected herds g u Location dependent 0.0012–0.04 mth−1 Fitted to observed numbers of generic herd tests.
Maximum probability of detecting an infected animal at slaughterhouse surveillance. a s 0.875
(0.70–1.00)
0.557–0.875 Estimate may be high because of factors and practices absent from the model, including approved finishing units and age effects [35, 36]. Sensitivity increased during 2008–2010.
Maximum probability of confirming an infected reactor. a c 0.40 N Fitted to number of OTFW (confirmed) breakdowns. This value underestimates the number of OTFW animals. (OTFW animals are unevenly distributed among breakdowns.)
Time required for lesions to reach maximum detectability. t Ls 35 d
(20–200) d
N This and other models seem to fit using a wide range of values for related parameters [22]. Reports that a high proportion of young reactors have visible lesions indicate a low value [36].
  1. See legend for Table 1. ‘S-T range’, i.e. ‘Spatial-temporal range’ indicates the actual range of values for the parameter used for the baseline fitted model in England and Wales during 2008–2010. ‘N’ indicates that only a single value was used for the parameter