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Infectious bronchitis virus (IBV) affects both vaccinated and unvaccinated flocks worldwide, with a significant impact on the poultry industry. The aim of the present study is to characterize an emerging variant pathogenic IBV originating from field outbreaks in vaccinated Egyptian layer flock. Samples were collected from disease-suspected flock with a history of administration of live and inactivated IBV vaccines (Ma5 type). Virus propagation in embryonated chicken eggs (ECEs), after three successive passages, revealed typical IBV lesions such as curling and dwarfism. The reported isolate was identified by a real-time reverse transcriptase PCR assay targeting nucleocapsid (N) gene and, further characterized by full-length spike (S1) gene sequencing. Phylogenetic analysis revealed clustering of the isolated virus within 4/91 genotype of GI-13 lineage. Deduced amino acid sequences identity revealed 75-76% and 88-90% similarity with the currently used classic (H120, Ma5, and M41) and variant vaccine strains (4/91 and CR88) in Egypt, respectively. Recombination analysis gave an evidence for distinct patterns of origin for the studied isolate providing another example of intra-genotypic recombination among IBVs and the first example of recombination within the GI-13 lineage in the Egyptian field. The studied isolate (IBV/CK/EG/Fadllah-10/2019) emerged as a result of recombination between the variant group (Egy/var I genotype, GI-23 lineage) as a major parent and the CR88 variant vaccine strain (4/91 genotype, GI-13 lineage) as minor parent. Our data suggest that both mutation and recombination may be contributing to the emergence of IBV variants which ascertain the importance of disease monitoring in vaccinated flocks as well as re-appropriation for the current vaccine strategies.

Emergence and genetic analysis of variant pathogenic 4/91 (serotype 793/B) infectious bronchitis virus in Egypt during 2019