Parameter definition | Symbol | Estimate (Range) | Source / Derivation |
---|---|---|---|
Initial number of undetected infected herds | Z | 4400 (1850–5050) | Fitted so that simulation matched the total number of breakdowns in 2008 within 100, i.e. between 4849 and 5049. |
Number of holdings in England and Wales with infectious environmental reservoirs. | N W | 7840 (SD ± 73) (5500–14,000) | Determined by the regional probabilities that individual holdings will have infectious environmental reservoirs (PW). |
Probability that individual holdings have infectious environmental reservoirs, dependent on a classification based on county and TB history. | P W | 0–0.828 | The probabilities are fitted to local breakdown frequencies, see Fig. 1 and Methods. |
Environment to cattle transmission rate per head of cattle at holdings with an infectious environmental reservoir. | h | 0.0006 (0.0004–0.004) mth− 1 | See Fig. 6. |
Cattle to cattle transmission rate (per month) per infected animal in a herd of 200 cattle. | β | 0.113 (0.10–0.14) mth− 1 | Fitted to observed numbers of reactor animals at disclosing tests in HRA and LRA. Close to a previously published estimate [22]. |
Power law determining degree of density dependence of cattle-cattle transmission. (0 matches density dependence, while a value of 1 matches frequency dependence.) | q | 0.5 (0.3–1.0) | Partial density dependence was demonstrated previously [22], but model outputs had low sensitivity to this parameter’s precise value. |
Probability of a persistent infection at the end of a breakdown in herds > 300 cattle, given that infected cattle remained after the disclosing test or there was at least 1 additional reactor. | c p | 0.6 (0.3–0.9) | Fitted to the observed number of breakdowns detected by post breakdown tests, especially in the Edge and Low Risk regions. Probability was lower in smaller herds, see Additional file 1. |