Necrotizing salpingitis in commercial laying hens associated with fowl adenovirus serotype 1 infection in China.

Fowl adenovirus serotype 1 (FAdV-A1) is a significant pathogen primarily associated with gizzard erosion and ulceration (GEU) in poultry. This study conducted a comprehensive epidemiological investigation of FAdV-A1 in 16,481 clinical samples collected from commercial poultry farms across 30 provinces in China between January 2022 and March 2026. The results revealed an overall FAdV-A1 detection rate of 0.36% (60/16,481), with 75% (45/60) of positive cases identified in laying hen flocks, predominantly during the onset to peak production phase (18-35 weeks of age). FAdV-A1 infection caused necrotizing salpingitis in affected hens, characterized by increased oviduct secretions, uterine edema, and necrosis and desquamation of glandular epithelial cells. Phylogenetic analysis based on the hexon gene demonstrated that all 19 sequenced FAdV-A1 isolates share 95.62-99.78% sequence identity with the apathogenic CELO strain. Serological analyses of AGP and VN revealed that antisera against currently circulating FAdV-C4 vaccine showed limited cross-neutralization against FAdV-A1 in vitro. FAdV-A1 challenge in laying hens induced characteristic necrotizing salpingitis lesions. This investigation demonstrates that FAdV-A1 is not restricted to causing GEU lesions but also elicits a previously unrecognized clinical manifestation of necrotizing salpingitis in Chinese laying hen flocks, thereby providing a scientific basis for accurate diagnosis, serological differentiation, and comprehensive prevention and control measures.