Abstract
BackgroundIn order to optimise the cost-effectiveness of active surveillance to substantiate freedom from disease, a new approach using targeted sampling of farms was developed and applied on the example of infectious bovine rhinotracheitis (IBR) and enzootic bovine leucosis (EBL) in Switzerland. Relevant risk factors (RF) for the introduction of IBR and EBL into Swiss cattle farms were identified and their relative risks defined based on literature review and expert opinions. A quantitative model based on the scenario tree method was subsequently used to calculate the required sample size of a targeted sampling approach (TS) for a given sensitivity. We compared the sample size with that of a stratified random sample (sRS) with regard to efficiency.ResultsThe required sample sizes to substantiate disease freedom were 1,241 farms for IBR and 1,750 farms for EBL to detect 0.2% herd prevalence with 99% sensitivity. Using conventional sRS, the required sample sizes were 2,259 farms for IBR and 2,243 for EBL. Considering the additional administrative expenses required for the planning of TS, the risk-based approach was still more cost-effective than a sRS (40% reduction on the full survey costs for IBR and 8% for EBL) due to the considerable reduction in sample size.ConclusionsAs the model depends on RF selected through literature review and was parameterised with values estimated by experts, it is subject to some degree of uncertainty. Nevertheless, this approach provides the veterinary authorities with a promising tool for future cost-effective sampling designs.
Highlights
In order to optimise the cost-effectiveness of active surveillance to substantiate freedom from disease, a new approach using targeted sampling of farms was developed and applied on the example of infectious bovine rhinotracheitis (IBR) and enzootic bovine leucosis (EBL) in Switzerland
A literature review on the epidemiology of IBR and EBL was conducted with a focus on specific risk factors (RF) for the diseases and their relevance for the Swiss cattle population, given that the population is considered to be free of these diseases
As all cattle farms are registered in the animal movement database (TVD), the chosen RF could be allocated to the affected farms by means of the TVD and the geographical software ArcGis 9, ArcMap Version 9.2 (ESRI Inc.) providing us with an Excel list (Microsoft Corporation 2007) of all 52,176 Swiss cattle farms and their corresponding RF for IBR and EBL for the year 2008
Summary
In order to optimise the cost-effectiveness of active surveillance to substantiate freedom from disease, a new approach using targeted sampling of farms was developed and applied on the example of infectious bovine rhinotracheitis (IBR) and enzootic bovine leucosis (EBL) in Switzerland. In Switzerland, annual serological surveys are conducted to substantiate freedom from infectious bovine rhinotracheitis (IBR), enzootic bovine leucosis (EBL), Brucella melitensis, Aujeszky’s disease and porcine reproductive and respiratory syndrome (PRRS). A very low prevalence is considered for sample size calculation and, in consequence, a large sample size is required to demonstrate freedom from disease [1]. This active surveillance approach is costly and personnel-intensive. The development of cost-effective tools for animal disease surveillance is of high interest to scientists and decision-makers in the field of veterinary public health
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