Full-length genome sequencing analysis of avian infectious bronchitis virus isolate associated with nephropathogenic infection

Infectious bronchitis virus (IBV) produces infectious bronchitis (IB) disease in poultry worldwide. In spite of proper vaccinations against the IBV, new IBV strains are continually emerging worldwide. In this study, a new highly virulent nephropathogenic IBV strain named CK/CH/XDC-2/2013 was identified from a vaccinated flock with clinical signs of IB in the Jiangsu province of China. The full-length genome sequence of the isolate was 27,714 nucleotides long, and the genome was organized similarly to classical IBV strains. Minimum divergence, phylogenetic analysis, and distance matrix of the genome showed that the CK/CH/XDC-2/2013 isolate had the highest similarity to the IBV BJ strain. The spike glycoprotein (S) gene had the greatest similarity to the nephropathogenic BJ strain and showed an 8 amino acid insertion (YSNGNSDV) at 73 to 80 sites and 3 amino acid deletion at sites 126 to 128 compared to the IBV vaccine strains. A recombination analysis of the S gene showed that the new isolate evolved from the IBV BJ strain and the KM91 vaccine strain. An animal challenge experiment showed a mortality of 60 to 80% in early-age chickens by different inoculation routes. Pathological examinations of the kidneys revealed inflammation, distention with uric acid deposits, and tubular degeneration. It indicated that the CK/CH/XDC-2/2013 isolate has robust kidney tissue tropism, and new nephropathogenic IBV strains are continuously evolving in China.