Comparative Genetic Sequencing Analysis of Infectious Bursal Disease Strains in Egypt: Insights into Their Molecular Evolution and Diversity based on Highly Variable Region

Document Type : Original Article

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1 Avian and Rabbit Diseases Department, Faculty of Veterinary Medicine, Benha University, Benha, Egypt.

2 Central Laboratory for Evaluation of Veterinary Biologics, Cairo, Egypt.

Abstract

Infectious bursal disease virus (IBDV) is an immunosuppressive virus for chicks especially 3-6 weeks of age. It is a double-stranded RNA virus which is characterized by continuous antigenic variation and mutation in its highly variable region (HVR) of viral protein 2. To investigate the molecular genotyping and the genetic relationships among the IBDV strains circulating in Egypt, bursae of six IBDV-positive samples collected from Qalubia, Gharbia, Giza, and Cairo provinces during 2018-2021 subjected to partial genomic sequencing of 620 bp HVR of VP2. The results revealed that all the sequenced samples clustered as genotype 3 of very virulent strains based on phylogenetic analysis. Comparing them to the other reference strains isolated from Egypt, they showed 97.9% to 100% nucleotide identity among them although there was 92.8% to 95.1% similarity with other reference genotype 3 strains isolated from other countries. They also recorded high divergence with other isolates from Egypt. In conclusion, this study highlights the endemic circulation of very virulent IBDV strains of genotype 3 which may be the main cause of the ineffectiveness of many used vaccines against IBDV due to the high antigenic diversity.

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