Preventief ruimen bij vogelgriep in pluimveedichte gebieden en mogelijkheden voor aanvullende bemonstering

Samenvatting

In the epidemic of highly pathogenic avian influenza (HPAI) in Dutch poultry in 2003, there was extensive between-farm transmission in the poultry-dense areas in the Gelderland valley and southeast Netherlands. Because the application of the minimum European control measures in these areas was not sufficient to prevent transmission, preventive culling was also carried out on a large scale. On the one hand, epidemiological modelling predicts that the risks of spread will be greatly reduced in 2023 compared to twenty years ago. On the other hand, this modelling predicts that there is still an area in the Gelderland valley where the application of the minimum European control measures may be insufficient to prevent intermediate transmission. The many dozens of HPAI outbreaks in the past year and a half, partly in the area in the Gelderland valley, give rise to the following three main questions: 1. The existing epidemiological model is supported by data from the major epidemic in 2003; and subsequently the current higher farm sizes and lower number of farms were taken into account. Is this model compatible with the recently observed outbreaks? 2. According to this model, what is the effect of preventive culling within a radius of 1 km in the area in the Gelderland valley? 3. To what extent can additional surveillance, in particular the sampling of dead animals, speed up the detection of outbreaks and thus reduce transmission risks compared to current surveillance? The current surveillance consists of (amongst other things) reporting enhanced mortality, and in the 3-km area around outbreaks also of sampling by NVWA and intensive telephone monitoring by GD. This report answers a total of five questions. The general conclusions are as follows: 1. The existing epidemiological model for HPAI spread between poultry farms in the Netherlands is well compatible with the observed outbreaks of HPAI in the Netherlands over the period September 2021 to September 2022. 2. The model predicts that preventive culling within 1 km will have the following effect on HPAI epidemics in the Gelderland valley: The average duration of the epidemic will be reduced from 51.4 to 43.9 days and the average total number of outbreak farms will be reduced from 14.6 to 9.7. However, this comes at a price, as according to these model analyses, the mean total number of culled farms will be higher for the preventive culling scenario: 44.8 farms (preventively culled farms and infected farms) compared to 14.6 farms (only infected farms) in the scenario without preventive culling. 3. According to a model analysis, bucket sampling on poultry farms can detect an HPAI outbreak on the farm earlier than the current notification system. The predicted reduction in the average time between introduction and detection is about 30 percent.