DEMONSTRATING FREEDOM OF DISEASE AFTER AN EMERGENCY VACCINATION CAMPAIGN WITH AN E2 SUB-UNIT MARKER VACCINE AGAINST CLASSICAL SWINE FEVER: A SIMULATION

摘要

The aim of this study was to simulate end screening after an emergency vaccination campaign with a marker vaccine against Classical Swine Fever (CSF). In each run of the model, it is assumed that 500 herds are vaccinated. The number of infected herdsand the number of infected animals within an infected herd are modelled as binomial distributions. The animal-level sensitivity and specificity are modelled as beta distributions. At each iteration the number of animals to be sampled in a herd is calculated in order to detect a minimal within herd prevalence (e.g. 1%) with a given level of confidence (e.g. 99%). The model indicates for each herd whether it is categorized as infected or not, based upon a given threshold of positive samples (e.g. 5%). Bycomparing these results to the simulated proportion of infected herds, it becomes possible to determine the herd sensitivity and specificity. If a herd prevalence of 5% and a within-herd prevalence of 2% are assumed, the highest combined herd sensitivity(HSe) (77.54%) and specificity (HSp) (74.45%) is obtained at the threshold level of 2%. If a threshold level of 5% is used the HSe decreases to 36.95%, whereas the HSp increases to 98.93%. Varying other parameters (e.g. expected within-herd prevalence,sample size) never results in a situation where an acceptably high HSe and HSp are combined. Therefore, further efforts are needed to improve herd level diagnostics. Also these results should be used to review available simulation models as the choice may influence the conclusions dramatically.