Modelling the control of bovine tuberculosis in badgers in England: culling and the release of lactating females.
A simulation model was used to evaluate the effect of different levels of culling on 6 badger social groups in an attempt to reduce or eradicate tuberculosis (TB) infection from the population. Apart from fecundity, all model parameters were derived from a comprehensive study of a naturally-infected badger population in England. Badger control was simulated using a trap-and-cull of 80% of all badgers in either 2 social groups (localized strategy) or all 6 social groups (wide area strategy). Lactating females were permitted to infect none or all of their young, to simulate the extremes of sow-to-cub (pseudo-vertical) transmission. Trapped lactating sows were either all released or all killed. Simulations where all infected badgers can be correctly diagnosed were also run to determine the importance of an improved live test for TB. In the absence of badger control, pseudo-vertical transmission increased the persistence and prevalence of TB in the simulated population. A single control operation was capable of eradicating TB from the population only if all 6 badger social groups were subjected to culling. If only infected individuals were killed, disease eradication was possible without a marked increase in population extinction. If all individuals were killed, the increased level of disease eradication occurred as a result of an increase in population extinction. Killing lactating badgers had no effect on the medium-term prevalence (up to 20 years) of the disease and resulted only in a reduced persistence of TB when a wide area badger control strategy was used.