Pathogen prevalence and health risks in European backyard poultry: a scoping review

Backyard poultry keeping has expanded across Europe, driven by increasing interest in locally produced eggs and meat. However, these small and often unregistered flocks may operate with limited veterinary supervision and variable biosecurity, creating opportunities for contact between domestic birds, commercial poultry, wildlife, and humans. Despite these concerns, evidence on pathogen occurrence in European backyard poultry systems remains scattered and heterogeneous.

This scoping review aimed to identify and synthesize the available evidence on pathogens reported in European backyard poultry flocks. Specifically, it sought to: (i) map reported occurrences of parasitic, bacterial, and viral pathogens; (ii) describe the diagnostic methods used; (iii) summarize factors associated with pathogen detection or transmission as reported in the included studies; and (iv) highlight methodological gaps and priorities for future surveillance and research.

The review was conducted according to PRISMA-ScR guidelines. Searches were performed in PubMed, CAB Abstracts, and Scopus up to July 2024. Studies conducted in Europe and focusing on backyard or small-scale poultry flocks were eligible if they reported pathogen occurrence, diagnostic methods, or associated factors. Thirty-three studies from 17 European countries met the inclusion criteria. Data extracted included study design, flock characteristics, pathogens investigated, diagnostic approaches, reported occurrence or prevalence values, and associated factors.

This review shows that a wide range of parasitic, bacterial, and viral pathogens has been reported in European backyard poultry flocks, including Eimeria spp., Dermanyssus gallinae, Mycoplasma gallisepticum, Salmonella spp., avian influenza virus, infectious bronchitis virus, and Marek's disease virus. Some studies reported high pathogen detection frequencies, and several associated factors were described, including outdoor access, multispecies keeping, contact with wild birds, and limited biosecurity. However, the evidence base remains fragmented due to uneven geographical coverage, predominantly cross-sectional study designs, frequent use of convenience sampling, heterogeneous diagnostic methods, and differences in sampling units. Therefore, the findings should be interpreted as a mapping of reported pathogen occurrence and associated factors, rather than as estimates of true European prevalence or evidence of reservoir status. Improved surveillance, harmonized diagnostic protocols, and longitudinal studies are needed to better characterize pathogen circulation and its implications for animal and public health within a One Health framework.