The QX-type avian infectious bronchitis virus (IBV) is still a prevalent genotype in Southwestern China. To analyze the antigenicity and pathogenicity characteristics of the dominant genotype strains (QX-type), S1 gene sequence analysis, virus cross-neutralization tests, and pathogenicity test of eight QX-type IBV isolates were conducted. Sequence analysis showed that the nucleotide homology between the eight strains was high, but distantly related to H120 and 4/91 vaccine strains. Cross-neutralization tests showed that all eight strains isolated from 2015 and 2017 belonged to the same serotype, but exhibited antigenic variations over time. The pathogenicity test of the five QX-type IBV isolates showed that only three strains, CK/CH/SC/DYW/16, CK/CH/SC/MS/17, and CK/CH/SC/GH/15, had a high mortality rate with strong respiratory and renal pathogenicity, whereas CK/CH/SC/PZ/17 and CK/CH/SC/DYYJ/17 caused only mild clinical symptoms and tissue lesions. Our results indicate that the prevalent QX-type IBVs displayed antigenic variations and pathogenicity difference. These findings may provide reference for research on the evolution of IBV and vaccine preparation of infectious bronchitis (IB).

Background: Clinical cases of hemangioma associated with subgroup J avian leukosis virus (ALV-J) have been reported in commercial chicken layer flocks since 2006. We attempted to reproduce hemangioma through experimental infection with ALV-J to evaluate viral pathogenicity in layer birds and their progenies. Results: Body weight and indexes for immune organs of chickens infected with ALV-J strain SCDY1 were lower than those in controls. Proliferation of lymphocytes was observed in many tissues, and viral integration was detected in the genome of lymphocytes at 14 days post-infection, along with virus shedding. ALV-J was also efficiently transmitted from eggs to progenies. Embryo hatchability and progeny mortality were lower than those for controls. The efficiencies of virus shedding and virus integration in the lymphocytes of progenies were higher than those in parents. Conclusions: ALV-J is able to inhibit the growth of infected chickens, and causes damage to immune organs. Vertical transmission of ALV-J appears to be more deleterious than horizontal transmission.