In the present study, we isolated a nephoropathogenic strain (IBYZ) in 2011. This strain was isolated, identified, and preserved from a large-scale chicken farm where an outbreak of IBV emerged in Jiangsu province. Chickens infected with the IBYZ strain showed severe kidney damage and a high mortality rate (Fig. 3B). The complete sequence has been deposited in the GenBank database under the accession number of KF663561. The S1 gene sequencing data indicated that the IBYZ strain belonged to the QX-like genotype (Fig. 8 ), with a nucleotide homology with the attenuated vaccine H120 strain of only 77.4%, and amino acid homology of 77.1%. Moreover, the S1/S2 cleavage site of IBYZ is HRRRR/S, which differed from RRFRR/S of the H120 vaccine strain. After whole-genome sequencing, we constructed a molecular clone strain using reverse genetic technology, termed rIBYZ. In addition, another strain used in this study is the live attenuated IBV vaccine, H120, and the molecular clone strain, rH120, which was constructed using the same method.
Fig. 8 Phylogenetic tree constructed based on the S1 gene of isolate ck/CH/IBYZ/2011 and 28 published IBV reference strains using the neighbor-joining method (Mega10.1.6).