Comparative risk-assessment of highly pathogenic avian influenza H5 viruses spread in French broiler and layer sectors

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   Peer Community in Animal Science

   Nov 17, 2025

   Avian influenza outbreaks pose a global threat, causing substantial economic losses and posing zoonotic risks to human health worldwide. Since 2015, France has confronted recurrent waves of highly pathogenic H5 avian influenza (HPAI), which have been originally introduced by migrating wild birds. The fattening duck sector—vital for “foie gras” production—is massively impacted [1–3]. In the duck sector, live bird movements between rearing, breeding, and force-feeding stages have been a major vector for virus dissemination. However, broiler and layer farms have also experienced significant outbreaks, with 329 cases reported in chicken farms between 2020 and 2022. Broiler and layer production systems differ significantly: broilers move directly from farm to slaughterhouse, while layers undergo two stages (pullet rearing and layer …

   Avian influenza outbreaks pose a global threat, causing substantial economic losses and posing zoonotic risks to human health worldwide. Since 2015, France has confronted recurrent waves of highly pathogenic H5 avian influenza (HPAI), which have been originally introduced by migrating wild birds. The fattening duck sector—vital for “foie gras” production—is massively impacted [1–3]. In the duck sector, live bird movements between rearing, breeding, and force-feeding stages have been a major vector for virus dissemination. However, broiler and layer farms have also experienced significant outbreaks, with 329 cases reported in chicken farms between 2020 and 2022. Broiler and layer production systems differ significantly: broilers move directly from farm to slaughterhouse, while layers undergo two stages (pullet rearing and layer production), necessitating live bird transport between sites. Even without such movements, indirect pathways—including contaminated equipment, feed delivery, egg collection, manure management, and human activity—present also high transmission risks [4, 5]. Direct human-bird contact, especially by veterinarians and staff working across multiple farms, remains particularly hazardous. The study from Hautefeuille and collaborators evaluates HPAI transmission risks within France’s broiler and layer sectors using the World Organization for Animal Health risk assessment framework [6]. This article is highly relevant to the One Health concept, which links environmental, animal and human health, and is also very timely. Data were collected through literature reviews and expert questionnaires (six to seven experts per questionnaire), with estimates combined using a Monte Carlo iterative process. The analysis focuses on indirect transmission routes—such as human contact, vehicle transport, and shared equipment—and examines how farm type, production stage, farming conditions, and integration level influence spread. Biosecurity’s impact on transmission probabilities is also assessed, with a sensitivity analysis further exploring its role. However, the study does not address cross-sector transmission. Results indicate quite surprisingly that, in the broiler sector, the highest transmission risk occurs between indoor farms, particularly those integrated within the same production association. Key pathways include personnel movement, feed transport, and manure management, even in farms with established biosecurity protocols. In the layer sector, free-range source farms pose the greatest risk to both indoor and free-range production farms, with egg transport and personnel movement as primary transmission routes. Sensitivity analysis confirms that higher biosecurity standards significantly reduce vulnerability as expected. These findings highlight the critical influence of farm type, integration, and biosecurity on virus spread, offering a foundation for targeted interventions—such as movement restrictions, enhanced biosecurity protocols, and vaccination—to mitigate future outbreaks and protect France’s poultry industry. The study’s key strengths are its quite innovative application of expert elicitation and scenario tree modeling to systematically rank HPAI transmission risks. This approach yields practical, evidence-based insights that can directly inform targeted risk management strategies. However, limitations include reliance on expert opinion rather than empirical data, potential biases from arbitrary assumptions, and a focus on relative rather than absolute risk. Also, the 2020 data may not fully reflect current HPAI dynamics. Overall, the study is representing a mature and valuable contribution to this important field of research for virologists, veterinarians, and specialists of avian and public health.

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   6.        Hautefeuille C, Muñoz F, Dauphin G, Paul M, Peyre M, Goutard F (2025) Comparative risk-assessment of highly pathogenic avian influenza H5 viruses spread in French broiler and layer sectors. bioRxiv, ver.6 peer-reviewed and recommended by PCI Animal Science. https://doi.org/10.1101/2024.09.11.612235

    

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   Version published to 10.1101/2024.09.11.612235 on bioRxiv

   Sep 14, 2024