Molecular characterization of variant infectious bronchitis virus in China, 2019: Implications for control programmes

Infectious bronchitis virus (IBV), an ongoing emergence enveloped virus with a single-stranded positive-sense RNA genome, belongs to the Gammacoronavirus genus in the Coronaviridae family. IBV-associated tracheitis, nephritis, salpingitis, proventriculitis and egg drop have caused devastating economic losses to poultry industry worldwide. Since the end of 2018, a remarkably increasing number of commercial broilers and layers, vaccinated or not, were infected with IBV in China. Here, we described two IB outbreaks with severe respiratory system or kidney injury in IBV-vaccinated commercial poultry farms in central China. Other possible causative viral pathogens, including avian influenza virus (AIV), Newcastle disease virus (NDV) and Kedah fatal kidney syndrome virus (KFKSV), were excluded by reverse transcription-polymerase chain reaction (RT-PCR), and three virulent IBV strains, HeN-1/China/2019, HeN-2/China/2019 and HeN-101/China/2019, were identified. Although the gross pathologic appearance of these two IB outbreaks was different, the newly identified IBV strains were all closely related to the ck/China/I0529/17 strain and grouped into GI-19 genotype clade based on the sequencing and phylogenetic analysis of the complete S1 genes. Moreover, there are still some evolutionary distance between the newly identified IBV strains, HeN-101/China/2019 in particular, and other GI-19 strains, suggesting that Chinese IBV strains constantly emerge and evolve towards different directions. In conclusion, this study provided an insight of the recently emerging IBV outbreaks in IBV-vaccinated commercial poultry farms and identified the genetic characteristics of three virulent GI-19 IBV strains, which shows the need to carry out proper preventive measures and control strategies.