Thesis (Ph.D.) - Cairo University - Faculty of Veterinary Medicine - Department of Animal Diseases

Four IBV isolates were detected by RT-PCR and were identified by sequence and phylogenetic analysis of portion of S1 gene from 17 chicken farms showing respiratory signs and variable mortalities in different Egyptian governorates. Two IBV isolates, IBV S40 and IBV S61, are related to Mass reference strains (Egypt/F/03, M41, H120, Ma5, and M52). However, IBV S78 and IBV S84 are related to Egyptian variant 2 IBV strains Ck/Eg/BSU-2/2011 and Ck/Eg/BSU-3/2011. In U.S., adaptation of an embryo-attenuated IBV ArkDPI-derived vaccine on CEK cells shifted the virus population towards homogeneity in spike (S) gene. The changes achieved in the S1 gene in CEKp7 were maintained after a back-passage in chickens or ECE. The homogeneous kidney cell-adapted IB ArkDPI vaccine confers effective protection against challenge; both eliminating emergence of vaccine subpopulations after vaccination and eliminating subpopulations after wild ark challenge. IBV cross-protection trials were also performed in healthy chickens maintained under controlled environmental conditions. Our results emphasized the need to include both single vaccination control groups and control groups primed and boosted with a single serotype when testing the efficacy of IBV protectotypes and/or novel IBV vaccine combinations against heterologous serotypes under controlled experimental conditions. Single vaccination with rLS/IBV.S2 (previously developed recombinant NDV La sota (rLS) expressing an IBV S2 transgene elicits a level of protection considerably less than the level of protection achieved by the prime and boost vaccination regime

Issued also as CD