title: A modelling framework for predicting the optimal balance between control and surveillance effort in the local eradication of tuberculosis in New Zealand wildlife.
abstract: Bovine tuberculosis (TB) impacts livestock farming in New Zealand, where the introduced marsupial brushtail possum (Trichosurus vulpecula) is the wildlife maintenance host for Mycobacterium bovis. New Zealand has implemented a campaign to control TB using a co-ordinated programme of livestock diagnostic testing and large-scale culling of possums, with the long-term aim of TB eradication. For management of the disease in wildlife, methods that can optimise the balance between control and surveillance effort will facilitate the objective of eradication on a fixed or limited budget. We modelled and compared management options to optimise the balance between the two activities necessary to achieve and verify eradication of TB from New Zealand wildlife: the number of lethal population control operations required to halt the M. bovis infection cycle in possums, and the subsequent surveillance effort needed to confidently declare TB freedom post-control. The approach considered the costs of control and surveillance, as well as the potential costs of re-control resulting from false declaration of TB freedom. The required years of surveillance decreased with increasing numbers of possum lethal control operations but the overall time to declare TB freedom depended on additional factors, such as the probability of freedom from disease after control and the probability of success of mop-up control, i.e. retroactive culling following detection of persistent disease in the residual possum population. The total expected cost was also dependent on a number of factors, many of which had wide cost ranges, suggesting that an optimal strategy is unlikely to be singular and fixed, but will likely vary for each different area being considered. Our approach provides a simple framework that considers the known and potential costs of possum control and TB surveillance, enabling managers to optimise the balance between these two activities to achieve and prove eradication of a wildlife disease, or the pest species that transmits it, in the most expedient and economic way. This cost- and risk-evaluation approach may be applicable to other wildlife disease problems where limited management funds exist.
authors.affiliation: Landcare Research, P.O. Box 69040, Lincoln 7640, New Zealand. Electronic address: gormleya@landcareresarch.co.nz.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Gormley
authors.affiliation: Landcare Research, P.O. Box 69040, Lincoln 7640, New Zealand.
authors.forename: E Penelope
authors.initials: EP
authors.lastname: Holland
authors.affiliation: Landcare Research, P.O. Box 69040, Lincoln 7640, New Zealand.
authors.forename: Mandy C
authors.initials: MC
authors.lastname: Barron
authors.affiliation: Landcare Research, P.O. Box 69040, Lincoln 7640, New Zealand.
authors.forename: Dean P
authors.initials: DP
authors.lastname: Anderson
authors.affiliation: Landcare Research, P.O. Box 69040, Lincoln 7640, New Zealand.
authors.forename: Graham
authors.initials: G
authors.lastname: Nugent
mesh_terms: D000818:Animals; D002417:Cattle; D062665:Epidemiological Monitoring / Q000662:veterinary; D058865:Introduced Species; D008962:Models, Theoretical; D009163:Mycobacterium bovis / Q000502:physiology*; D009520:New Zealand; D011155:Population Control / Q000191:economics; D011159:Population Surveillance / Q000379:methods*; D018570:Risk Assessment / Q000191:economics; D048330:Trichosurus; D014380:Tuberculosis, Bovine / Q000382:microbiology / Q000517:prevention & control*
keywords: Eradication; Expected cost; Mycobacterium bovis; Surveillance; Trichosurus vulpecula; Tuberculosis; Wildlife disease