Risk maps for the spread of highly pathogenic avian influenza in poultry

Abstract

Devastating epidemics of highly contagious animal diseases such as avian influenza, classical swine fever, and footand-mouth disease underline the need for improved understanding of the factors promoting the spread of these pathogens. Here the authors present a spatial analysis of the between-farm transmission of a highly pathogenic H7N7 avian influenza virus that caused a large epidemic in The Netherlands in 2003. The authors developed a method to estimate key parameters determining the spread of highly transmissible animal diseases between farms based on outbreak data. The method allows for the identification of high-risk areas for propagating spread in an epidemiologically underpinned manner. A central concept is the transmission kernel, which determines the probability of pathogen transmission from infected to uninfected farms as a function of interfarm distance. The authors show how an estimate of the transmission kernel naturally provides estimates of the critical farm density and local reproduction numbers, which allows one to evaluate the effectiveness of control strategies. For avian influenza, the analyses show that there are two poultry-dense areas in The Netherlands where epidemic spread is possible, and in which local control measures are unlikely to be able to halt an unfolding epidemic. In these regions an epidemic can only be brought to an end by the depletion of susceptible farms by infection or massive culling. The analyses provide an estimate of the spatial range over which highly pathogenic avian influenza viruses spread between farms, and emphasize that control measures aimed at controlling such outbreaks need to take into account the local density of farms.

Evaluation of interventions and vaccination strategies for low pathogenicity avian influenza: spatial and space–time analyses and quantification of the spread of infection

“…In the Italian and Dutch HPAI epidemics of 1999-2000 and 2003, respectively, local transmission played an important role [1,11,28]. However, our results on the extent of clustering in the 2002-2003 LPAI epidemic (within 60 km, with a peak at 20 km) could be a consequence of a medium and long-distance spread of the infection due to the transmission of AI viruses through the contact structure of the poultry production sector (i.e.…”

“…However, when combined with other control measures such as vaccination, the effectiveness increased (Table 1, epidemic 3, periods [10][11][12]. In fact, these two measures are not designed to directly lower the risk of infection at the farm level or in the area where the epidemic was still in progress ; instead, they are meant to reduce contacts between farms in areas where the virus has been introduced, decreasing the risk of the massive spread of infection.…”

“…To evaluate the effectiveness of measures for controlling HPAI epidemics, both spatial analyses and estimates of the basic reproduction ratio (R 0 ) have been adopted [1,11,12]. Spatial analyses have been used to generate hypotheses regarding AI risk factors and to identify areas at higher risk of infection, through the detection of spatial and space-time clusters.…”

Farmers’ willingness to invest in livestock disease control: the case of voluntary vaccination against bluetongue

“…Small values of represent global transmission and high values depict transmission kernels with primarily local spread (Boender et al, 2007;de Koeijer et al, 2011).…”

“…The epidemiology of BT is modelled by a stochastic spatial explicit susceptible-latent-infectious-recovered (SLIR) model, in which the probability of transmission from an infectious farm to a susceptible farm is a function of interfarm distance and the infectious period (Boender et al, 2007;de Koeijer et al, 2011).…”