Impact of palmiped farm density on the resilience of the poultry sector to highly pathogenic avian influenza H5N8 in France

Abstract

We analysed the interplay between palmiped farm density and the vulnerability of the poultry production system to highly pathogenic avian influenza (HPAI) H5N8. To do so, we used a spatially-explicit transmission model, which was calibrated to reproduce the observed spatio-temporal distribution of outbreaks in France during the 2016–2017 epidemic of HPAI. Six scenarios were investigated, in which the density of palmiped farms was decreased in the municipalities with the highest palmiped farm density. For each of the six scenarios, we first calculated the spatial distribution of the basic reproduction number (R0), i.e. the expected number of farms a particular farm would be likely to infect, should all other farms be susceptible. We also ran in silico simulations of the adjusted model for each scenario to estimate epidemic sizes and time-varying effective reproduction numbers. We showed that reducing palmiped farm density in the densest municipalities decreased substantially the size of the areas with high R0 values (> 1.5). In silico simulations suggested that reducing palmiped farm density, even slightly, in the densest municipalities was expected to decrease substantially the number of affected poultry farms and therefore provide benefits to the poultry sector as a whole. However, they also suggest that it would not have been sufficient, even in combination with the intervention measures implemented during the 2016–2017 epidemic, to completely prevent the virus from spreading. Therefore, the effectiveness of alternative structural preventive approaches now needs to be assessed, including flock size reduction and targeted vaccination.

New Patterns for Highly Pathogenic Avian Influenza and Adjustment of Prevention, Control and Surveillance Strategies: The Example of France

“…Reducing density, particularly of ducks, in areas with very high densities, is a measure that has been identified as a potential major improvement by ANSES's expert appraisal work [49], as well as by modeling research [50]. During the 2022-2023 season, voluntary or involuntary reductions in density appear to have had a major effect on the size of epizootics.…”

Vaccination of poultry against highly pathogenic avian influenza – part 1. Available vaccines and vaccination strategies

“…The initiation of HPAI vaccination in poultry is also influenced by the characteristics of the susceptible poultry population. Factors such as a high density of poultry farms, which can lead to multiple poultry outbreaks caused by secondary spread, play a significant role (Boender et al., 2007 ; Dorigatti et al., 2010 ; Lambert et al., 2022 ; Bauzile et al., 2023 ). The spatial distribution of poultry in Europe is presented in Figure 8 and highlights the regions with the highest densities of chickens (scattered relatively across Europe) and ducks (in particular France and Hungary).…”