Evolution of New Variant Strains of Infectious Bronchitis Virus Isolated from Broiler Chickens

In order to investigate the prevalence and track the genetic evolutions of the circulated infectious bronchitis virus (IBV) strains and their prevalence in Assiut, Egypt, partial S1 gene amplification and sequencing were done during 2013-2014. Three infectious bronchitis virus (IBV) strains with the following accession numbers (KR003438, KR003439 and KR003440 respectively) were detected from 21 tracheal samples originated from suspected broiler flock with a percentage of infection 14.28%. Nucleotide sequencing and analyses of the hypervariable region of the S1 subunit of the virus spike gene showed that the three isolates, shared from 94.3% to 99.3% homologies between each other. 46.5 to 84.6% similarities were observed with the global reference strains which reflected the variant nature of the three isolated viruses. In their comparison with the commonly used vaccine strains (793/B and Massachusetts types) the isolates revealed low nucleotide homologies ranged from 66.3 to 85.7% which the lower values 67% to 69.8% were mentioned with the most used vaccinal strain H120 that explain the farness of isolated viruses from vaccines used in Egypt. The pathogenicity testing of the 3 IBV isolates in 30-day-old chickens revealed the respiratory nature of these strains with mortality percentages 20-30%. These results demonstrates for the first time in Assiut province, the variant nature of the circulated IBV serotypes associated with disease cases and its farness from the used vaccinal strains that emphasize the importance of continued monitoring of IBV to optimize the vaccination strategies to lay a good foundation for developing vaccines having strains genetically close related to the circulated field viruses.