Isolation and Molecular Characterization of Infectious Bronchitis Virus (IBV) Variants Circulating in Commercial Poultry in Pakistan

Avian infectious bronchitis is a contagious viral disease of chicken. It is present everywhere in the world where poultry is reared. This study was designed to detect, isolate and sequence the circulating Infectious bronchitis viruses (IBVs) in poultry in Pakistan. Out of 905 clinical specimens tested, 358 were found positive for IBV, having serotype distribution of Mass (43%), 4/91 (51%), and different variants of IBV (5%), respectively. One of the variants recovered from broiler-breeder (BB) flock and designated as Pak-973, was further propagated and characterized on molecular basis. Virus neutralization test did not neutralize it with the reference antisera IBV serotypes M41, 4/91, D274, D1466 and IT-02, identifying it as a distinct serotype. Furthermore, Haemagglutination Inhibition test (HI) has proven useful in differentiating various serotype of IBV. In addition to this, partial Spike 1 (S1) gene was amplified by reverse transcriptase-PCR (RT-PCR) and subjected to sequencing for determining its genetic diversity. Sequenced data was submitted in the GenBank and the IBV isolate named as KX013102_NARC/973_Pakistan_2015. The phylogenetic analysis of Pak-973 showed a maximum homology of 93% with the Indian IBV variant KF360983_23/B/2008_India. However, an overall nucleotide homology with some other Indian isolates is between 82-93%. This study revealed the presence of IBV variant isolates in the field in Pakistan during 2015.