Genetic Characterization of Egyptian Field Isolates of Infectious Bursal Disease Virus

Abstract

Detection and characterization of field infectious bursal disease virus (IBDV) isolates circulating among different broiler breeds representing three Egyptian governorates with a history of vaccination against IBDV, was done during 2013- 2015. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to amplify and produce clear band of 620 Base pair (bp) product within the hypervariable region of the IBDV viral protein (VP2) gene. The IBDV was prevalent in thirty out one hundred flocks (30%). Subsequently, chosen PCR products were subjected to further analysis by sequencing and phylogenetic studies. Amino acid substitution in VP2 region used to establish a clear framework on the epidemiology of isolated IBDV . Genetic analysis showed that all examined IBDV isolates characterized as vvIBDV had amino acids residues(222A, 242I, 256I, 294I, 299S) which showed to be unique for all vvIBDV strains and clustered phylogenetically with the previously Egyptian IBDVs ( 99.3-100% ) identity. While, vaccinal IBDV strains (BURSA-VAC and UNIVAX) were clustered in another group with (91.1–91.9%), (91.9–92.6%) identity respectively which might leads to vaccination failure and reemergence of disease. Consequently, we recorded wide range of genetic similarities (94.8-95.6) with the recombinant vaccines (VP2 of Faragher 52/70) seed virus, which showed superior protective efficacy against recent Egyptian vvIBDV isolates. IBDV is still a threat against poultry industry. It is important to keep track on appearance and evolution of antigenically different IBDV circulating strains followed by regular updating of the vaccination strategy.