A virulent infectious bronchitis virus (IBV), designated as CK/CH/GD/QY16 (referred as QY16), was isolated from a diseased chicken farm in Guangdong province, China, in 2016. The complete genome of the strain was sequenced and analyzed. The results show that the genome of QY16 consists of 27,670 nucleotides, excluding poly (A) tail, and that its genome organization is 5' UTR-1a-1b-S-3a-3b-E-M-4b-4c-5a-5b-N-6b-3' UTR-poly (A) tail. Sequence comparison among QY16 and other IBV strains was conducted and its results demonstrate that the S1 gene of QY16 has the highest nucleotide sequence identity with that of 4/91, and the other part of its genome is highly similar to that of YX10. The results of the phylogenic analysis show that the entire genome of QY16 and most of the QY16 genes are located in the same cluster as those of YX10, except for the S1 gene which is located in the same cluster with that of 4/91. It has been further confirmed by the RDP and SimPlot analysis that QY16 is a recombinant strain deriving from YX10 (as the major parental sequence) and 4/91 (as the minor parental sequence), and that the recombination occurs in a region which includes the 3'-terminal 1b sequence (85 nt) and the 5'-terminal S1 protein gene sequence (1,466 nt). The results of the vaccination-challenge test suggest that QY16 is a nephropathogenic strain of IBV and that the vaccine strains-H120 and 4/91-cannot provide effective protection against it. These results indicate that the continuing evolution of IBV strains by genetic drift and genetic recombination may lead to IBV outbreaks even among the vaccinated chickens in China.

No abstract

Avian infectious bronchitis virus ( IBV ) is causing considerable economic losses in the world poultry industry. The main difficulty of prevention and control of IB disease is the numerous genotypes and serotypes. The genetic analysis of IBV was mainly based on the S1 gene which played an important role in infectivity. In the study, One hundred and thirty-nine strains of avian infectious bronchitis virus were isolated from chickens showing signs of disease in southern China during the period from April 2019 to March 2020. The nucleotide and amino acid sequences from the isolated field strains were compared to 22 published references. Nucleotide homologies ranged from 64.5% to 100% and amino acid homologies ranging from 70% to 99.8%. Six genotype IBV strains were co-circulating in southern China. QX-type was still the most dominant genotype. Alignment of nucleotide and amino acid sequences of S1 gene revealed that the substitutions, insertions and deletions are widely among isolated strains. Recombination analysis showed that there is a large number of recombinant strains amongst these isolates, forming new sub branches, subtypes and variants. Therefore, long-term continuing surveillance is necessary for IBV prevention and control.

The infectious bronchitis virus ( IBV ) is an acute and highly contagious disease, which affects chickens of all ages. Vaccination is the most important way to control this disease. Nevertheless, novel variant strains are constantly reported because of the lack of proofreading capabilities of RNA polymerase and high frequency of homologous RNA recombination. Cross-protection studies has demonstrated that the vaccines could provide great protective effects against viruses of same serotype or genotype. However, the protective effect of different commercial vaccines and vaccine combinations against the prevalent IBV strains in China has rarely been studied. Owing to the multiple genotype or serotype IBV strains prevalence in China, the polyvalent vaccines and their composition were used to expanding the protection spectrum of vaccine in practical application. To evaluate the protection of Chinese commercial IBV polyvalent vaccines against prevalent strains (QX-like and TW I-like), an immune challenge test was conducted. Four polyvalent vaccines, containing 4/91, H120, YX10p90, LDT3-A, and 28/86, were combined to form 8 vaccination strategies, almost all of which could provide more than 70% protection effects against challenge with QX-like strain. Particularly, the best protection rate (93%) was generated by administration the polyvalent vaccine C (H120 + 28/86 + 4/91) at 1 D of age and the polyvalent vaccine B (H120 + 4/91 + YX10p90) at 10 D of age. However, all the vaccination strategies in this study cannot provide great protective effects against TW-like strain, and more vaccines should be included in studies to expand the protection spectrum of vaccine. Therefore, for the newly emerging IBV strains, immunization with polyvalent vaccines via different vaccination strategies could be used to control the prevalence of IBV in a short time, whereas developing the homologous vaccines was not always necessary.