Molecular–Serologic Snapshot of a Silent Respiratory Threat: Avian Metapneumovirus Circulation in Unvaccinated Broiler Breeders in Egypt, 2024-2025

Background Avian metapneumovirus (aMPV) is an economically significant respiratory pathogen of poultry that affects performance, egg production, and fertility of breeder flocks. Despite its impact, aMPV continues to be ill-defined in Egypt with no integrated surveillance studies conducted in breeder flocks. Therefore, the current study was designed to provide the first comprehensive molecular and serological assessment of aMPV circulation in broiler breeders in Egypt. Methods Between 2024 and 2025, 6,000 serum samples and 800 tracheal swabs were collected from 60 unvaccinated broiler breeder flocks across twelve Egyptian governorates. Sera were obtained at 16 weeks (rearing phase) and 35 weeks (production phase) of age and screened for aMPV subtypes A and B by ELISA. Tracheal swabs collected during the production phase were pooled into 80 composite samples and tested for the viral RNA by RT-qPCR. Results Serological analysis revealed widespread aMPV exposure, with flock-level seroprevalence ranging between 94.0% and 97.4%. Antibody titers increased between 16 and 35 weeks, reflecting cumulative viral exposure. Molecular testing detected aMPV RNA in 67 (83.75%) of pooled swabs. Subtype B was the predominant genotype detected solely in 65 (81.25%) sample pools and mixed with subtype A in 2 pools (2.5%). Serological and molecular findings were generally aligned, with flocks positive for aMPV RNA often exhibiting higher antibody titers. Conclusion These findings indicate that aMPV, particularly subtype B, is likely endemic across the Egyptian broiler breeder flocks. The study highlights critical knowledge gaps, emphasizing the need for viral isolation, sequencing, and controlled evaluation of biosecurity and vaccination strategies.