Molecular characterization of pathogenic 4/91-like and QX-like infectious bronchitis virus infecting commercial poultry farms in Indonesia

Background and Aim: Existing data on the characteristics of infectious bronchitis virus (IBV) gathered throughout Indonesia have been recognized to indicate variants similar to globally distributed vaccine strains. Despite past and current intensive vaccination programs, IBV infections in the country's poultry industry have not been effectively controlled. Therefore, this study aimed to investigate the genotype of several isolates based on partial S1 gene sequences. In particular, the investigation is directed to focus on layer chickens in actively vaccinated farms indicating IBV symptoms. Materials and Methods: Samples were isolated from ten different layer chicken flocks experiencing respiratory problem, drops in egg production, and a "penguin-like" stance, which were collected from commercial poultry farms in Central Java and Yogyakarta regions, Indonesia, within the periods of 2012-2018. Fragment of the S1 gene of IBV sampled from actively vaccinated commercial poultry farms was amplified using primer 5'-aca tgg taa ttt ttc aga tgg-3' (forward) and 5'-cag att gct tac aac cac c-3' (reverse) with the length of polymerase chain reaction (PCR) product at 383 bp. The sequence of samples was then compared with the sequence of reference S1 gene nucleotides of IBV from NCBI GenBank database. The amino acid analysis and multiple alignment sequence were conducted using Mega X. Results: During necropsy, enlargement of the oviduct and swollen kidney were observed. Reverse transcription-PCR diagnosis of their 383 bp S1 gene showed that all samples were IBV positive. Phylogenetic analysis of the S1 gene discovered seven samples to be clustered as 4/91-like strains. Meanwhile, the remaining three samples were grouped in QX-like strain cluster. Conclusion: This study is a pioneering report providing molecular evidence of pathogenic QX-like and 4/91-like strains circulating in Indonesia. Findings discovered, in this study, strongly suggested the importance of improving protections by available IBV vaccines through updated circulating strain clusters. It is critical to ensure the delivery of an effective control measurement of and vaccination protocols against IBV infections in the country's commercial poultry industry in particular and worldwide in general.