Assessing the Effectiveness of Tuberculosis Management in Brushtail Possums (<i>Trichosurus vulpecula</i>), through Indirect Surveillance of<i>Mycobacterium bovis</i>Infection Using Released Sentinel Pigs

Nugent, Graham; Yockney, Ivor; Whitford, E. J.; Cross, Martin L.

doi:10.1155/2014/361634

Cited by 8 publications

(5 citation statements)

References 44 publications

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“…Radio telemetry is then used to relocate them on a number of subsequent occasions, and any resident uncollared pigs that they have become associated with are shot. This Judas method facilitates location and shooting of feral pigs at approximately twice the rate of untargeted hunting (Nugent et al ., 2014 ). With the available range of hunting techniques, it is feasible to maintain feral pig populations at very low densities in most areas, but deliberate control of feral pig populations has not been applied for TB management purposes in New Zealand.…”

Section: Ecology and Epidemiology Of Tb In Wild Deer And Feral Pigsmentioning

confidence: 99%

“…3–4 pigs per pig home range) is sufficient to provide 95% confidence that TB is not present in possums over the same area (Nugent and Whitford 2008a ). The high sensitivity of pigs as sentinels has supported the deliberate release of radio-tagged TB-free pigs for disease surveillance purposes (Nugent et al 2002 ), and sometimes these pigs' movements have been tracked by radio-collaring them with GPS-transmitting devices to better define the area “surveyed” (Nugent et al 2011c ), and sometimes to help locate non-collared sympatric resident pigs for sampling (Yockney and Nugent 2006 ; Nugent et al ., 2014 ).…”

Section: Roles Of Wild Deer and Feral Pigs In The New Zealand Tb Contmentioning

confidence: 99%

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The epidemiology ofMycobacterium bovisin wild deer and feral pigs and their roles in the establishment and spread of bovine tuberculosis in New Zealand wildlife

Nugent

Gortázar²,

Knowles³

2015

New Zealand Veterinary Journal

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In New Zealand, wild deer and feral pigs are assumed to be spillover hosts for Mycobacterium bovis, and so are not targeted in efforts aimed at locally eradicating bovine tuberculosis (TB) from possums (Trichosurus vulpecula), the main wildlife host. Here we review the epidemiology of TB in deer and pigs, and assess whether New Zealand's TB management programme could be undermined if these species sometimes achieve maintenance host status.In New Zealand, TB prevalences of up to 47% have been recorded in wild deer sympatric with tuberculous possums. Patterns of lesion distribution, age-specific prevalences and behavioural observations suggest that deer become infected mainly through exposure to dead or moribund possums. TB can progress rapidly in some deer (<10%), but generalised disease is uncommon in wild deer; conversely some infected animals can survive for many years. Deer-to-deer transmission of M. bovis is rare, but transmission from tuberculous deer carcasses to scavengers, including possums, is likely. That creates a small spillback risk that could persist for a decade after transmission of new infection to wild deer has been halted.Tuberculosis prevalence in New Zealand feral pigs can reach 100%. Infections in lymph nodes of the head and alimentary tract predominate, indicating that TB is mostly acquired through scavenging tuberculous carrion, particularly possums. Infection is usually well contained, and transmission between pigs is rare.Large reductions in local possum density result in gradual declines (over 10 years) in TB prevalence among sympatric wild deer, and faster declines in feral pigs. Elimination of TB from possums (and livestock) therefore results in eventual disappearance of TB from feral pigs and wild deer. However, the risk of spillback infection from deer to possums substantially extends the time needed to locally eradicate TB from all wildlife (compared to that which would be required to eradicate disease from possums alone), while dispersal or translocation of pigs (e.g. by hunters) creates a risk of long-distance spread of disease. The high rate at which pigs acquire M. bovis infection from dead possums makes them useful as sentinels for detecting TB in wildlife.It is unlikely that wild deer and feral pigs act as maintenance hosts anywhere in New Zealand, because unrestricted year-round hunting keeps densities low, with far less aggregation than on New Zealand farms. We conclude that active management of wild deer or feral pigs is not required for local TB eradication in New Zealand.

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Section: Ecology and Epidemiology Of Tb In Wild Deer And Feral Pigsmentioning

confidence: 99%

Section: Roles Of Wild Deer and Feral Pigs In The New Zealand Tb Contmentioning

confidence: 99%

The epidemiology ofMycobacterium bovisin wild deer and feral pigs and their roles in the establishment and spread of bovine tuberculosis in New Zealand wildlife

Nugent

Gortázar²,

Knowles³

2015

New Zealand Veterinary Journal

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“…Although we compared only two alternative surveillance tools here (leg‐hold traps alone, or DDs (chew‐cards) with follow‐up trapping), there are other options for surveillance of residual M. bovis infection in possums in New Zealand—most notably—the use of wildlife spillover hosts as sentinels for persistent infection (e.g., feral pigs and ferrets and wild deer; Nugent, ; Anderson et al., ). In particular, feral pigs are especially sensitive detectors of persistent M. bovis infection in possums (Nugent, Gortazar, & Knowles, ; Nugent, Whitford, & Young, ; Nugent, Yockney, Whitford, & Cross, ), so where they are abundant and inexpensive to procure—a high stopping threshold would be optimal.…”

Section: Discussionmentioning

confidence: 99%

Cost-based optimization of the stopping threshold for local disease surveillance during progressive eradication of tuberculosis from New Zealand wildlife

Gormley

Anderson

Nugent

2017

Transbound Emerg Dis

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Bovine tuberculosis (TB) is managed in New Zealand largely via population reduction of the major wildlife disease reservoir of Mycobacterium bovis, the introduced brushtail possum Trichosurus vulpecula. New Zealand aims to eradicate M. bovis infection from its livestock and wildlife within 40 years, as the culmination of progressive regional eradication programmes. Declarations of regional eradication are decided after extensive possum population control and post-control surveillance; hence, we developed a modelling framework, based on eco-epidemiological simulation data, to provide cost-evaluated options for deciding when to make these declarations. A decision-support framework evaluated potential costs of wildlife surveillance (and recontrol, if required) with respect to the calculated probability of successful eradication of M. bovis from wildlife. This enabled expected costs to be predicted in terms of stopping thresholds, allowing selection of optimal stopping rules based on minimizing costs. We identified factors that could influence optimal stopping values applied during regional eradication. Where vector/disease surveillance was inexpensive (for example, using low-cost detection devices or sentinel wildlife hosts) optimization involved setting a higher rather than lower stopping value, as it would be cheaper to minimize the risk of making a false declaration of eradication than to remedy any such failure. In addition, any cost of recontrol would largely depend on the time to rediscovery of residual M. bovis infection in wildlife, which would in turn be linked to the level of ongoing passive surveillance (with more rapid detection of re-emergent infection among wildlife in farmland situations than in remote forested regions). These two scenarios would favour different optimal stopping rules, as would the consideration of stakeholder confidence and socio-political issues, which are discussed. The framework presented here provides guidance to assess the economics underlying eradication of bovine TB from New Zealand farming; this eliminates reliance upon a pre-determined and uniform stopping rule for ceasing active management.

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“…Potential data sources to inform this modelling will include disease status of livestock in adjacent pastures, direct possum and sentinel surveys along forest/pasture margins, and data from sentinel animals (usually pigs) deliberately released into a surveillance area that can be tracked using VHF (very high frequency) and GPS (global positioning system) telemetry, and later recaptured to be tested for TB (Nugent et al . 2014 ). Additionally, and ideally, comparison of a range of freedom estimation model outcomes with predictions from sampling statistics would be undertaken on a research-basis across different habitat types, to provide more accurate descriptions of population size for the wildlife species (possums or sentinels) under consideration in each different area.…”

Section: Modelling That Integrates Surveillance Information From Multmentioning

confidence: 99%

Development of integrated surveillance systems for the management of tuberculosis in New Zealand wildlife

Anderson

Ramsey

Lisle

et al. 2015

New Zealand Veterinary Journal

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Disease surveillance for the management of bovine tuberculosis (TB) in New Zealand has focussed, to a large extent, on the development of tools specific for monitoring Mycobacterium bovis infection in wildlife. Diagnostic techniques have been modified progressively over 30 years of surveillance of TB in wildlife, from initial characterisation of gross TB lesions in a variety of wildlife, through development of sensitive culture techniques to identify viable mycobacteria, to molecular identification of individual M. bovis strains. Of key importance in disease surveillance has been the elucidation of the roles that different wildlife species play in the transmission of infection, specifically defining brushtail possums (Trichosurus vulpecula) as true maintenance hosts compared to those that are predominantly spillover hosts, but which may serve as useful sentinel species to indicate TB persistence. Epidemiological modelling has played a major role in TB surveillance, initially providing the theoretical support for large-scale possum population control and setting targets at which control effort should be deployed to ensure disease eradication. As TB prevalence in livestock and wildlife declined throughout the 2000s, more varied field tools were developed to gather surveillance data from the diminishing possum populations, and to provide information on changing TB prevalence. Accordingly, ever more precise (but disparate) surveillance information began to be integrated into multi-faceted decision-assist models to support TB management decisions, particularly to provide informed parameters at which control effort could be halted, culminating in the Proof of Freedom modelling framework that now allows an area to be declared TB-free within chosen confidence limits. As New Zealand moves from large-scale TB control to regional eradication of disease in the coming years, further integrative models will need to be developed to support management decisions, based on combined field data of possum and TB prevalence, sentinel information, risk assessment in relation to financial benefits, and changing political and environmental needs.

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Assessing the Effectiveness of Tuberculosis Management in Brushtail Possums (Trichosurus vulpecula), through Indirect Surveillance ofMycobacterium bovisInfection Using Released Sentinel Pigs

Cited by 8 publications

References 44 publications

The epidemiology ofMycobacterium bovisin wild deer and feral pigs and their roles in the establishment and spread of bovine tuberculosis in New Zealand wildlife

The epidemiology ofMycobacterium bovisin wild deer and feral pigs and their roles in the establishment and spread of bovine tuberculosis in New Zealand wildlife

Cost-based optimization of the stopping threshold for local disease surveillance during progressive eradication of tuberculosis from New Zealand wildlife

Development of integrated surveillance systems for the management of tuberculosis in New Zealand wildlife

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