Some novel field isolates belonging to lineage-1 of the genotype GI-avian infectious bronchitis virus (AIBV) show strong evidence of recombination with field/vaccinal strains.

Abstract

Avian infectious bronchitis virus (AIBV) infection remains one of the significant challenges for the poultry industry due to the high rates of morbidity, mortality, and poor production performance. The AIBV genome is prone to frequent changes due to the possibility of drift and recombination between various genotypes. Despite the massive administration of several types of vaccines, many outbreaks of AIBV continue to be reported worldwide. One of the major goals of this study was to monitor genetic changes in the viral genomes of some recent field isolates of the AIBV from broiler chickens. To achieve these goals, we tested several pools of tissue specimens (trachea and kidneys) from some suspected AIBV outbreaks in broiler chickens by quantitative real-time PCR (q-RT-PCR). We selected two samples, one from the trachea (IBV-4) and one from the kidney (AIBV-6), for the next-generation sequencing (NGS). The full-length genomes of these two isolates were deposited in the GenBank (Accession Numbers: PQ468962 and PQ468963). The viral genome size of AIBV-4 and AIBV-6 was 27,475 and 27,469 nucleotides in length. AIBV-4 have typical AIBV genome organization (5'UTR, ORF1a, ORF1b, S, 3a, 3b, E, M, 4b, 5a, 5b, N, and 3'UTR), while AIBV-6 lack 5b. These two AIBV isolates belong to sublineage-1 of the genotype GI-1 based on the phylogenetic using the full-length, the S, and the N protein sequences. The S1/S2 cleavage sites show polybasic amino acid sequences (RR-F-RR) as direct evidence of virulence of these isolates. The analysis shows multiple recombination events of these isolates with some natural and vaccine strains. The potential major parent for both AIBV-4 and AIBV-6 was AIBV Beaudette. Active and vigilant monitoring of the AIBV sequences of the currently circulating strains in chickens is highly encouraged to help develop novel vaccines and diagnostic assays that match the field circulating strains.