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The application for a poultry compartment by VPI and the prospect of further ones motivates the Dutch Ministry of Economic Affairs and the Netherlands Food and Consumer Product Safety Authority to raise the following three questions: 1) What are the additional transmission risks that the (specific) VPI compartment poses during an HPAI epidemic, compared to a situation without compartment?; 2) What are the additional transmission risks that a compartment in general poses during an HPAI epidemic, depending on its characteristics?; 3) What are relevant evaluation criteria for granting the compartment status? In this study we addressed these questions by quantitatively assessing the veterinary risks based on mathematical model calculations, and by qualitatively discussing the (socio) economic aspects.

As livestock farms in The Netherlands are nowadays being scaled up in size for economic reasons, the question becomes important how disease introduction risks and risks of onward transmission scale with farm size (i.e. with the number of pigs on the farm). Here we use the epidemic data of the 1997-1998 epidemic of Classical Swine Fever Virus (CSF) in The Netherlands to address this question for CSF risks. This dataset is one of the most powerful ones statistically as in this epidemic a total of 428 pig farms were infected (with the majority of farm sizes ranging between 27 and 1750 pigs). We have extended the earlier models for the transmission risk as a function of between-farm distance, by adding two size dependent factors: these factors describe the farm size dependence of, respectively, the susceptibility of an exposed farm and the infectivity of a source farm. Using the best-fitting model, we show that the size of a farm has a significant influence on both farm-level susceptibility and infectivity for CSF. Although larger farms are both more susceptible to CSF and, when infected, more infectious to other farms than smaller farms, the increase is less than linear. According to the best-fitting model, the higher the farm size, the smaller the effect on the susceptibility and infectivity of a farm of increments in farm size. We show that this implies, based on the pig farming characteristics of 1997-1998 in The Netherlands and assuming that the relative spatial distribution of farm locations does not change, a trend towards less but larger farms would produce a net decrease in between-farm transmission risks.

Dit artikel is een samenvatting van het rapport "Laag pathogene aviaire influenza virus iInfecties op pluimveebedrijven in Nederland" (CVI 2012). Dit rapport is geschreven naar aanleiding van vragen van het toenmalige Ministerie van Economische zaken, Landbouw en Innovatie. De vragen die werden gesteld zijn: - hebben pluimveebedrijven met vrije uitloop een grotere kans op introductie van LPAI virus infecties?; - is de kans op introductie gerelateerd aan wilde vogels?; - is er een periode in het jaar waarin het risico op infectie groter is? - kunnen er factoren geidentificeerd worden die de kans op introductie verminderen?

Laag Pathogene Aviaire Influenza (LPAI) is een aandoening bij pluimvee die wordt veroorzaakt door LPAI virussen. In Nederland worden elk jaar meer infecties met LPAI virussen op pluimveebedrijven gedetecteerd. In dit rapport is gekeken naar een aantal mogelijke oorzaken voor deze toename. Het vermoeden bestaat dat serologisch en/of virologisch positieve bedrijven vaker dan gemiddeld bedrijven zijn met vrije uitloop. De vraag is of dit werkelijk zo is, en zo ja welke maatregelen dan genomen kunnen worden om de kans op een introductie op een bedrijf met vrije uitloop te verminderen.

Rift Valley Fever (RVF) is a zoonotic vector-borne infection and causes a potentially severe disease in both humans and young animals. The Ministry of Economic Affairs, Agriculture and Innovation (EL&I) is interested in the risk of an outbreak of Rift Valley Fever virus (RVFV) for the Netherlands, and more knowledge is needed about the risk of introduction of the virus, the risk of spread (transmission) of the virus in the country once introduced, and the methods for control and surveillance. For this purpose, a mathematical model was developed to study (1) the probability of a RVF outbreak at different days of introduction during the year, (2) the probability of persistence of the infection during the entire year, and (3) outbreak size and duration at different days of introduction during the year.