Novel Taiwan-I-type infectious bronchitis virus: First evidence of testicular atrophy and efficacious protection with strain-matched oil-emulsified inactivated vaccine

The Taiwan-I-type infectious bronchitis virus (IBV) has become one of the most dominant and threatening genotypes circulating in China poultry farms. In this study, we characterized the Taiwan-I-type IBV strain GX-NN200723 and evaluated its pathogenicity and vaccine potential. Phylogenetic and recombination analyses revealed that the strain shared the highest nucleotide similarity with the vaccine strain QXL87 and originated from a recombination event between CK/CH/LSC-99I (major parent) and TW2575/98 (I) (minor parent) within the S1 gene region. Notably, epitope mapping showed significant differences in the number and sequence of antigenic sites compared to commonly used vaccine strains (H120, 4/91, QXL87, LDT3-A), and these differences may largely account for the poor cross-protection and frequent vaccine failures observed in the field. Pathogenicity assessment in 7-day-old SPF chicks demonstrated broad tissue tropism of the strain, causing 30% mortality along with severe reproductive disorders, notably, testicular atrophy in males was observed for the first time in Taiwan-I-type IBV. Furthermore, an oil-emulsified inactivated vaccine (OEIV) developed from the GX-NN200723 strain induced strong humoral and cell-dependent immune responses. Protective efficacy was only evaluated against homologous challenge in this study, the GX-NN200723-OEIV group exhibited 100% survival, the mildest clinical signs, minimal pathological damage, and the lowest viral shedding among all immunized groups. These findings support the use of the GX-NN200723-OEIV as a promising candidate vaccine for controlling Taiwan-I-type IBV infection. This study provides critical insights into the evolution, pathogenesis, and immunization strategies against this economically significant poultry pathogen.