Water birds play a crucial role in disseminating and amplifying avian influenza viruses (AIVs) in the environment. However, they may have limited interactions with domestic facilities, raising the hypothesis that other wild birds may play the bridging role in introducing AIVs into poultry. An ornithocoenosis study, based on census-transect and camera-trapping methods, was conducted in 2019 in ten poultry premises in northeast Italy to characterize the bird communities and envisage the species that might act as bridge hosts for AIVs. The data collected were explored through a series of multivariate analyses (correspondence analysis and non-metric multidimensional scaling), and biodiversity indices (observed and estimated richness, Shannon entropy and Pielou’s evenness). The analyses revealed a high level of complexity in the ornithic population, with 147 censused species, and significant qualitative and quantitative differences in wild bird species composition, both in space and in time. Among these, only a few were observed in close proximity to the farm premises (i.e., Magpies, Blackbirds, Cattle Egrets, Pheasants, Eurasian Collared Doves, and Wood Pigeons), thus suggesting their potential role in spilling over AIVs to poultry; contrarily, waterfowls appeared to be scarcely inclined to close visits, especially during autumn and winter seasons. These findings stress the importance of ongoing research on the wild–domestic bird interface, advocating for a wider range of species to be considered in AIVs surveillance and prevention programs.

Comprehensive understanding of the patterns and drivers of avian influenza outbreaks is pivotal to inform surveillance systems and heighten nations’ ability to quickly detect and respond to the emergence of novel viruses. Starting in early 2017, the Italian poultry sector has been involved in the massive H5N8 highly pathogenic avian influenza epidemic that spread in the majority of the European countries in 2016/2017. Eighty‐three outbreaks were recorded in north‐eastern Italy, where a densely populated poultry area stretches along the Lombardy, Emilia‐Romagna and Veneto regions. The confirmed cases, affecting both the rural and industrial sectors, depicted two distinct epidemic waves. We adopted a combination of multivariate statistics techniques and multi‐model regression selection and inference, to investigate how environmental factors relate to the pattern of outbreaks diversity with respect to their spatiotemporal and genetic diversity. Results showed that a combination of eco‐climatic and host density predictors were associated with the outbreaks pattern, and variation along gradients was noticeable among genetically and geographically distinct groups of avian influenza cases. These regional contrasts may be indicative of a different mechanism driving the introduction and spreading routes of the influenza virus in the domestic poultry population. This methodological approach may be extended to different spatiotemporal scale to foster site‐specific, ecologically informed risk mitigating strategies.

Between October 2021 and April 2022, 317 outbreaks caused by highly pathogenic avian influenza (HPAI) H5N1 viruses were notified in poultry farms in the northeastern Italian regions. The complete genomes of 214 strains were used to estimate the genetic network based on the similarity of the viruses. An exponential random graph model (ERGM) was used to assess the effect of ‘at-risk contacts’, ‘same owners’, ‘in-bound/out-bound risk windows overlap’, ‘genetic differences’, ‘geographic distances’, ‘same species’, and ‘poultry company’ on the probability of observing a link within the genetic network, which can be interpreted as the potential propagation of the epidemic via lateral spread or a common source of infection. The variables ‘same poultry company’ (Est. = 0.548, C.I. = [0.179; 0.918]) and ‘risk windows overlap’ (Est. = 0.339, C.I. = [0.309; 0.368]) were associated with a higher probability of link formation, while the ‘genetic differences’ (Est. = −0.563, C.I. = [−0.640; −0.486]) and ‘geographic distances’ (Est. = −0.058, C.I. = [−0.078; −0.038]) indicated a reduced probability. The integration of epidemiological data with genomic analyses allows us to monitor the epidemic evolution and helps to explain the dynamics of lateral spreads casting light on the potential diffusion routes. The 2021–2022 epidemic stresses the need to further strengthen the biosecurity measures, and to encourage the reorganization of the poultry production sector to minimize the impact of future epidemics.

Effective control of avian diseases in domestic populations requires understanding of the transmission dynamics facilitating viral emergence and spread. In 2016–17, Italy experienced a significant avian influenza epidemic caused by a highly pathogenic A(H5N8) virus, which affected domestic premises housing around 2.7 million birds, primarily in the north‐eastern regions with the highest density of poultry farms (Lombardy, Emilia‐Romagna and Veneto). We perform integrated analyses of genetic, spatiotemporal and host data within a Bayesian phylogenetic framework. Using continuous and discrete phylogeography, we estimate the locations of movements responsible for the spread and persistence of the epidemic. The information derived from these analyses on rates of transmission between regions through time can be used to assess the success of control measures. Using an approach based on phylogenetic–temporal distances between domestic cases, we infer the presence of cryptic wild bird‐mediated transmission, information that can be used to complement existing epidemiological methods for distinguishing transmission within the domestic population from incursions across the wildlife–domestic interface, a common challenge in veterinary epidemiology. Spatiotemporal reconstruction of the epidemic reveals a highly skewed distribution of virus movements with a high proportion of shorter distance local movements interspersed with occasional long‐distance dispersal events associated with wild birds. We also show how such inference be used to identify possible instances of human‐mediated movements where distances between phylogenetically linked domestic cases are unusually high.

Wild aquatic birds are crucial in maintaining the high pathogenicity avian influenza (HPAI) viruses. However, the HPAI dynamic at the wild‐domestic interface is still poorly known, and a comprehensive understanding of species that could potentially act as a bridge between wetlands and poultry farms is still lacking. In this study, an eco‐epidemiological framework was used to build species distribution models for 40 wild bird species camera‐trapped at 10 poultry farms in northeastern Italy. The predicted wild bird favorability distributions were used to estimate HPAI outbreak occurrences in the area of interest, using an ensemble approach that included five methodologies: generalized linear model (GLM), generalized additive model (GAM), boosted regression trees (BRTs), random forest (RF), and maximum entropy (MaxEnt). The group of species that included most of the Ardeidae (i.e., great egret, purple heron, little egret, and cattle egret), one Galliformes (i.e., common pheasant), and one Gruiformes (i.e., common moorhen) showed the highest importance (IMP = 28%) in explaining the HPAI outbreak probability of occurrence in poultry, highlighting their potential bridging role between the reservoir species and the domestic populations. The second most important group of species (IMP = 17%) included one Anseriformes (i.e., mallard), two Charadriiformes (i.e., black‐headed gull and yellow‐legged gull), and one Ardeidae (i.e., gray heron), remarking their role in the disease ecology. These results underline the complex role of the wild‐domestic interface in the epidemiology of HPAI, suggesting that a broader range of species than what is typically considered might be involved in HPAI virus ecology. Including these groups of species in targeted surveillance programs would help in fine‐tuning sampling efforts and identifying early warning signals of possible transmission to poultry holdings.

The ongoing global spread of highly pathogenic avian influenza (HPAI) continues causing major impacts on poultry, wildlife, and public health. Among the most affected countries in Europe, Italy experienced three major epidemic waves in 2016–23, caused by 2.3.4.4b H5N8 and H5N1 subtypes. Yet, the underlying spatio-temporal dispersal dynamics and drivers of these epidemics remain to be elucidated. Here, we combined viral genome sequencing with continuous phylogeographic inference to reconstruct the evolutionary and spatio-temporal history of these epidemics. By combining genetic data with landscape, poultry-related variables, and wild bird abundances, we explored how the environment was associated with viral diffusion in space and time. We identified distinct diffusion patterns and environmental associations across the three epidemics. The first two waves (2016–17 and 2021–22) were dominated by local poultry-to-poultry transmission in high-density farming areas, with agricultural areas being significantly associated with a relatively higher viral lineage dispersal velocity in 2021–22. In contrast, the most recent wave (2022–23) showed evidence of mid- to long-distance dispersal events positively associated with wetlands, waterbodies, and gull abundances, pointing to a larger role of wild birds in HPAI spatial dynamics. The estimated weighted diffusion coefficients and spatial wavefront distances revealed a shift from localised poultry-driven to long-distance spread, likely related to wild birds. Our findings highlight a progressive shift from poultry-driven epidemics to more complex environmental transmission dynamics involving wild birds and natural habitats. These changes underscore the need to adapt surveillance and control strategies to an evolving and ecologically diverse viral landscape.