Identification of a novel recombinant virulent avian infectious bronchitis virus

Abstract

The emergence of new infectious bronchitis virus (IBV) variants is often disastrous in the poultry industry. In this study, an IBV, CK/CH/2010/JT-1, was isolated from an H120- and 4/91-IBV-vaccinated flock in China. Antisera against vaccine strains H120 and 4/91 could not provide effective protection against CK/CH/2010/JT-1 in virus neutralization assays. CK/CH/2010/JT-1 could cause 43.75% mortality with respiratory and severe renal lesions in inoculated chickens. Phylogenetic analysis of the S1 gene showed that CK/CH/2010/JT-1 and 31 other isolates could be grouped as a new genotypic cluster. Recombination analysis revealed that three recombination events could be found in the genome of CK/CH/2010/JT-1 at positions 24709-365, 17160-19811 and 21136-21770. Whole-genome sequence analysis showed that CK/CH/2010/JT-1 originated from multiple template switches among QX-like, CK/CH/LSC/99I-, tl/CH/LDT3/03- and 4/91-type IBVs. All of these data demonstrated that CK/CH/2010/JT-1 is a new recombinant genotype IBV with high virulence. Our findings suggest that the surveillance of new genotype strains of IBV is very important for developing more effective anti-IBV strategies.

Keywords: Genome; Infectious bronchitis virus; Recombinant; Virulence.

Fig. 1

Phylogenetic tree of the S1 gene from infectious bronchitis viruses (IBVs). A phylogenetic tree was constructed with the UPGMA method using MEGA version 5.05. Bootstrap values were determined from 1000 replicates of the original data. The CK/CH/2010/JT-1 strain is marked with a black solid triangle, and strains described in BLASTN analysis are marked with black hollow triangles.

Fig. 2

Simplot (A) and Bootscan (B) analyses of the complete genomic sequence of strain CK/CH/2010/JT-1. Reference strains partridge/GD/S14/2003 (red), 4/91 (yellow), ck/CH/LDL/091022 (blue) and GX-YL5 (brown) were used as putative parental strains. The y-axis gives the percentage of identity or permuted trees respectively, and the x-axis gives the location of the query sequence. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Evolution analysis of strain CK/CH/2010/JT-1. (A) Phylogenetic trees of the S1 gene and genomic positions 366-17159, 19812-21135, 21771-23867, and 23868-24708 of ck/CH/2010/JT-1 by the neighbour-joining method using MEGA version 5.05. (B) Recombination process of strain CK/CH/2010/JT-1′s genome sequence. CK/CH/LSC/99I-type (brown), QX-like (blue), tl/CH/LDT3/03-type (red) and 4/91-type (yellow) strains. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

Chickens experimentally infected with IBV isolate CK/CH/2010/JT-1. (A) Survival of chickens after inoculation with IBV strain CK/CH/2010/JT-1. (B) Antibody responses to IBV in sera at 28 days post-inoculation.

Fig. 5

Gross lesions in trachea and kidney tissues from chickens experimentally infected with IBV strain CK/CH/2010/JT-1. A, normal trachea control; B, tracheas of dead chickens at 8 dpi showed haemorrhage with serous catarrhal exudates; C, normal kidney control; D, kidneys of dead chickens at 8 dpi showed swollen tubules and ureters distended with excess urate.

Fig. 6

Histopathologic analysis (haematoxylin-eosin stain) of chickens infected with IBV strain CK/CH/2010/JT-1. A, normal trachea tissue control; B, trachea tissue infected with CK/CH/2010/JT-1 displays extensive dropout, degeneration, and necrosis of ciliated epithelial cells and lymphocytic infiltration (black arrow). Scale bar = 50 μm; C, normal lung tissue control; D, lung tissue infected with CK/CH/2010/JT-1 displays haemorrhage and congestion (black arrow). Scale bar = 200 μm; E, normal kidney control; F, kidney tissue infected with CK/CH/2010/JT-1 displays severe renal lesions, including degeneration, necrosis of renal tubular epithelial cells, and exfoliated renal tubular epithelial cells (black arrow). Scale bar = 50 μm.