BIO-MOLECULAR IDENTITY OF CIRCULATED STRAIN OF INFECTIOUS BRONCHITIS VIRUS (IBV) IN VACCINATED BROILER CHICKEN

Document Type : Research article

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Virology Department, Fac. Vet. Medicine, Beni-Suef University, Egypt.

Abstract

Infectious bronchitis virus (IBV) is regarded as one of the most deleterious viruses, inducing high risk in the poultry industry worldwide, including Egypt. The present study aimed to detect the biological and molecular characteristics of IBV in samples collected from vaccinated broilers in Beni-Seuf Governorate during 2023. The virus propagated on SPF-embryonated chicken eggs (ECE), after the fifth passage, the characteristic pathological lesions, such as dwarfing and curling of the infected embryos, were observed. The trypsin-induced hemagglutination test (THA) and reverse transcriptase polymerase chain reaction (RT-PCR), amplification of partial Spike-1 glycoprotein, sequencing, partial identity, and phylogenetic tree were performed to achieve this aim. The amplification of a partial Spike-1 glycoprotein and phylogenetic tree assigned the isolate to genotype I, clade 23 (S1: GI-23), and submitted it to GenBank as Egypt/Beni/Suef/05 Egyptian IBV strain with accession no.: OR471645. Sequencing analysis showed a high degree of similarity to previously isolated Egyptian strains, such as OP585566 F1282-6 Egypt 2022) 100, 100%(, EG/VVT.NRC_Egypt_2021 (96.9, 98.4%) and MN967774 Bens/AR07 Egypt 2019 (97.6 ,98.7%) of nucleotide and amino acid sequences, respectively. In conclusion, the present IBV strain during 2023 clustered in GI. 23 lineages are still circulating in susceptible or vaccinated broiler chickens, causing persistent infection to poultry flocks. Despite broad vaccination regimes, this strain is virulent to broilers, leading to serious mortalities and morbidity, altering the economic situation of local industry in Egypt. Efficient vaccination providing cross-protection against the circulating genotype is based on the genotyping, serotyping, and protectotyping in a collective manner, but not in a separate manner.

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