Abstract
Highly pathogenic avian influenza (HPAI) continues to be a severe on-going threat to domestic and wild birds, with the French poultry sector experiencing both animal health and economic impacts every year. Current between-farm transmission dynamics have been mechanistically explained through farm populations having species-dependent infectivity and susceptibility. During the 2016-2017 French epidemic, dynamic models have shown that duck farms were both more infective and susceptible to HPAI than poultry farms. However, aviculture farms differ across more qualities than only species presence, including rearing practices and environmental exposure, flock sizes, and temporal activity periods. Differences in infectivity and susceptibility among duck farms are hypothesized to be related to indoor and outdoor farming practices, as different stages in the production cycle occur in different environments. Further, differences in individual farm contribution to epidemic propagation is hypothesized to be explained through farm size. To test these hypotheses, we developed an individual-based, spatially-explicit, deterministic model of HPAI transmission that accounts for the varying periods of activity and inactivity among farms, and also considers the dynamic nature of outdoor raising restrictions. This model is currently being parameterized to 2021–22 historical epidemic data of southwest France, and will be used to elucidate transmission rates, relative susceptibility, and relative infectivity of the different types of duck farms. The discovered parameters will then be fed into stochastic models to explore alternative epidemic outcomes across different biosecurity scenarios, such moving the pre-fattening stage of foie gras duck raising exclusively indoors, or instituting various poultry vaccination strategies.