Real Time Detection of Different Variant Strains of Infectious Bronchitis Virus in Trachea, Lung and Kidney of Infected Broiler Chickens

BACKGROUND: Avian infectious bronchitis virus (IBV) has a great potential for genetic variability which leads to the generation of new virus strains. The changes in the IBV genome often cause alterations in virulence, tissue tropism, and viral replication in the host tissues. OBJECTIVES: This study was conducted to identify the virus variant strains in the trachea, lungs, and kidneys of infected birds. The possible relationship of IBV variants with the relative quantity of virus in each organ was also investigated. METHODS: The IBV variant strains were detected by polymerase chain reaction (PCR) and direct sequencing. Amongst infected commercial broiler flocks sampled at Golestan and Mazandaran provinces of Iran, nine flocks (three flocks per variant) were selected based on the identified variants. Trachea, lung, and kidney samples of five birds per flock were examined for the presence of the virus and variants. Moreover, the virus was quantified in target organs using real-time quantitative PCR. RESULTS: Based on the results of PCR and sequencing, three IBV variants were selected, namely A, B, and C. Virus types A and B were detected in all target organs, while type C was detected in the trachea and kidney. Virus type C had the highest quantity of 17.02±5.22 and virus type A showed the lowest quantity of 5.68±2.4 in infected tissues. The relative quantity of virus detected in tissues significantly correlated with the IBV variant. CONCLUSIONS: Genetic polymorphism in IBV field strains was revealed to have significant correlations with viral quantity in the lung, trachea, and kidney. Our findings are an update of the current knowledge on the associa-tions between viral genotype, virulence, and pathogenicity.