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 generating new virus strains. The changes in IBV genome often cause alterations in the virulence, tissue tropism and viral replication in the host tissues. OBJECTIVES: This study was conducted to identify the virus variant strains in trachea, lung and kidney of infected birds. The possible relationship of IBV variants with the relative quantity of virus in each organ was also investigated.METHODS: IBV variant strains were detected by polymerase chain reaction (PCR) and direct sequencing. Amongst samples collected during one season (spring), from infected commercial broiler flocks located at Golastan and Mazandaran province of Iran, 9 flocks (3 flocks per each variant) were selected based on the identified variants. Trachea, lung and kidney samples of 5 birds per flock were examined for the presence of virus and variants. Virus also quantified in target organs using relative quantitative real time PCR.RESULTS: Based on the PCR and sequencing, three IBV variants were selected (A, B and C). Virus type A and B were detected in all target organs but virus type C detected in trachea and kidney. Virus type C had the highest quantity (17.02 ± 5.22) and virus type A showed the lowest quantity (5.68 ± 2.4) in infected tissues. Relative quantity of virus detected in tissues significantly correlated with IBV variant. CONCLUSIONS: Genetic polymorphism at IBV field strains has revealed significant correlations with viral quantity in lung, trachea and kidney. Our finding is an update of current knowledge on the associations between viral genotype, virulence and pathogenicity.