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【Objective】A disease model of fowl adenovirus serotype 2 (FAdV-2) was established to provide a refference for evaluating the immunogenicity and vaccine effectiveness of FAdV-2.【Method】The samples suspected to be infected with avian adenovirus were isolated and identified. The genetic evolution of the Fiber and Hexon gene sequences of the isolates was analyzed. The nucleotide and amino acid sequences of the isolated strain and other FAdV representative strains were analyzed using DNAStar and MEGA7.0. After determining that the isolated virus was FAdV-2, the pathogenicity of the isolated strain was analyzed in 6-week-old SPF chickens under different infection routes and different infection doses in animal experiment. The best infection model and infection dose were selected to establish the FAdV-2 pathogenesis model.【Result】One FAdV-2 strain was successfully isolated from the infected chicken tissue samples, named KM strain. Genetic evolution analysis shows that KM strain and GX01 strain belong to the FAdV-2 of avian adenovirus species D of group Ⅰ. The homology analysis shows that the nucleotide similarity of Fiber gene and Hexon gene between KM strain and GX01 strain is 98.9% and 99.3%, and the amino acid similarity is 98.9% and 98.8%, respectively. The pathogenicity of intravenous injection was higher than that of intramuscular injection, and the chickens showed obvious hepatitis hydropericardium syndrome (HHS). The infection route of the KM strain model was intravenous injection, and the infection dose was 108.0TCID50. The chickens died after infection, with a mortality rate of 50%. Obvious pathological changes were found in the dead chickens at necropsy, and the chickens were positive for cloaca virus shedding at 1 d post infection. The established KM strain disease model provides a certain reference for vaccine development and vaccine evaluation, which will effectively prevent and reduce the transmission of FAdV-2.【Conclusion】It is verified that FAdV-2 can cause hepatitis hydropericardium syndrome, and a pathogenesis model of FAdV-2 infection in SPF chickens is established for the first time.

【Objection】This study aimed to monitor the genetic variation and molecular evolutionary trends of H9N2 avian influenza virus (AIV) in Guangdong, and provide reference data for the evolutionary analysis and prevention and control of H9N2 AIV in China.【Method】The HA and NA genes of three H9N2 AIV strains isolated from Guangdong in 2022 were amplified, cloned, and sequenced. The DNAStar and PhyloSuite software were used for sequence assembly and alignment. The MEGA, Megalign, NetNGlyc 1.0 Server, and other software were used for genetic evolution, percent identity, receptor binding, protein activity, drug resistance, and glycosylation site analysis of their nucleotide and amino acid sequences.【Result】The phylogenetic tree showed that the HA gene of the three isolates belonged to the clade h9.4.2.5 and the NA gene belonged to the clade 1. However, the nucleotide homology with the early strain was only 81.6%~91.7% and 88.2%~91.2%, formed new clade named clade h9.4.2.5c and clade 1.2, respectively. The nucleotide and amino acid sequence analysis revealed that the HA cleavage site was PSRSSR ↓ GLF. The receptor binding site underwent I155T, H183N, A190T/V, T212I, Q226L, and Q227M mutations. The glycosylation site underwent 218N non-glycosylation and acquired new glycosylation site at 313N. The NA stalk showed nine nucleotides deletion at positions 187-195 (ACAGAGATA), leading to the loss of three amino acids at positions 63-65 (TEI). The absorbtion site of NA on red blood cells showed K/E/S368N and D369N mutations. No related mutations to neuraminidase activity and drug resistance were found at the E119, D151, R152, R224, E276, R292, and R371.【Conclusion】The HA and NA genes of the three H9N2 AIV isolated from Guangdong in 2022 had evolved into a new subgroup. Some mutaitons suggest that prevalent H9N2 in Guangdong may enhanc adaptability of mammals and its antigenicity has changed. Moreover, it has not yet acquired resistance to durgs oseltamivir and zanamivir.