Avian infectious bronchitis (IB), caused by avian infectious bronchitis virus (IBV), is an acute and highly contagious disease that is extremely harmful to the poultry industry throughout the world. The cross-using of different attenuated live vaccine strains has led to the occurrence of diverse IBV serotypes. In this study, we isolated an IBV strain from a chicken farm in southwest China and designated it CK/CH/SCMY/160315. Construction of a phylogenetic tree based on full S1 gene sequence analysis suggested that CK/CH/SCMY/160315 bears similarity to GI-28, and further comparison of S1 amino acid residues revealed that CK/CH/SCMY/160315 showed mutations and deletions in many key positions between LDT3-A and other GI-28 reference strains. Importantly, CK/CH/SCMY/160315 was identified as a novel recombinant virus derived from live attenuated vaccine strains H120 (GI-1), 4/91 (GI-13), LDT3-A (GI-28), and the field strain LJL/08-1 (GI-19), identifying at least 5 recombination sites in both structural and accessory genes. Pathogenicity analysis indicated that CK/CH/SCMY/160315 caused listlessness, sneezing, huddling, head shaking, and increased antibody levels in the inoculated chickens. To further describe pathogenicity of this novel strain, we assessed viral load in different tissues and conducted hematoxylin and eosin (HE) staining of the trachea, lungs and kidneys. Our results provide evidence for the continuing evolution of IBV field strains via genetic recombination and mutation, leading to outbreaks in the vaccinated chicken populations in China.

Infectious bronchitis virus (IBV) and Newcastle disease virus (NDV) are two poultry pathogens seriously affecting the poultry industry. Here, IBV S1 and the ectodomain of NDV F proteins were separately linked with the trans-membrane and carboxy-terminal domain of IBV S protein (S_TMCT), composing rS and rF; thus, a novel chimeric infectious bronchitis-Newcastle disease (IB-ND) virus-like particles (VLPs) vaccine containing the rS, rF, and IBV M protein was constructed. Under the transmission electron microscope (TEM), VLPs possessing similar morphology to natural IBV were observed. To evaluate the immunogenicity of chimeric IB-ND VLPs, specific pathogen-free (SPF) chickens were immunized with three increasing doses (50, 75, and 100 μg protein of VLPs). Results of ELISAs detecting IBV and NDV specific antibodies and IL-4 and IFN-γ T cell cytokines indicated that vaccination with chimeric IB-ND VLPs could efficiently induce humoral and cellular immune responses. In the challenge study, chimeric IB-ND VLPs (100 μg protein) provided 100% protection against IBV or NDV virulent challenge from death, and viral RNA levels in tissues and swabs were greatly reduced. Collectively, chimeric IB-ND VLPs are highly immunogenic and could provide complete protection from an IBV or NDV virulent challenge. Chimeric IB-ND VLPs are an appealing vaccine candidate and a promising vaccine platform bearing multivalent antigens.

Avian coronavirus infectious bronchitis virus (IBV) causes severe economic losses in the poultry industry, but its control is hampered by the continuous emergence of new genotypes and the lack of cross-protection among different IBV genotypes. We designed a new immunogen based on a spike with the consensus nucleotide sequence (S_con) that may overcome the extraordinary genetic diversity of IBV. S_con was cloned into a pVAX1 vector to form a new IBV DNA vaccine, pV-S_con. pV-S_con could be correctly expressed in HD11 cells with corresponding post-translational modification, and induced a neutralizing antibody response to the Vero-cell-adapted IBV strain Beaudette (p65) in mice. To further evaluate its immunogenicity, specific-pathogen-free (SPF) chickens were immunized with the pV-S_con plasmid and compared with the control pVAX1 vector and the H120 vaccine. Detection of IBV-specific antibodies and cell cytokines (IL-4 and IFN-γ) indicated that vaccination with pV-S_con efficiently induced both humoral and cellular immune responses. After challenge with the heterologous strain M41, virus shedding and virus loading in tissues was significantly reduced both by pV-S_con and its homologous vaccine H120. Thus, pV-S_con is a promising vaccine candidate for IBV, and the consensus approach is an appealing method for vaccine design in viruses with high variability.