Isolation and characterization of a fowl adenovirus 2 (FAdV-2) strain YN2497 associated with lethal hydropericardium-hepatitis syndrome in neonatal chickens in China.

Since 2015, the detection rate of fowl adenovirus (FAdVs), including FAdV-2, has increased steadily in China, posing growing challenges to the prevention and control of avian diseases. In this study, an FAdV strain, designated YN2497, was isolated from chickens in Yunnan Province, China, and its genomic characteristics and pathogenicity were investigated. Whole-genome sequencing and comparative phylogenetic analysis confirmed that strain YN2497 belongs to serotype FAdV-2 within the species Fowl Aviadenovirus D. Experimental infection of 1-day-old specific-pathogen-free (SPF) chicks induced typical hydropericardium-hepatitis syndrome (HHS), with viral shedding detected in both oral and cloacal swabs starting at 1-day post-infection. Notably, infection caused 100% mortality in day old chicks and was associated with severe gross and histopathological lesions. These findings demonstrate the high susceptibility of neonatal chickens to this FAdV-2 strain and provide relevant information for understanding age-dependent FAdV-2-associated disease and developing effective control strategies.