Molecular Characterization Of Infectious Bursal Disease Virus From Commercial Poultry In Pakistan

Infectious bursal disease (IBD) is an immunosuppressive disease of young, growing chickens which results in impaired growth or mortality of rearing flocks. In the current era there is a re-emergence of very virulent Infectious Bursal Disease Viruses (vvIBDV) and classical variant (cv) IBDV strains which increased the financial losses of poultry industry worldwide. Recent studies were conducted to characterize the existing vvIBDVs prevailing in Pakistan. The suspected samples were collected from the field outbreaks during the period from 2014–2017. IBDV was detected by RT-PCR. The sequences of VP2 gene (hyper variable region) were determined and available details were aligned with sequences submitted inGenBank. Phylogenetic analysis reveals that both vvIBDV and classical variant strains were circulating in different regions of Pakistan. In Indo-Pak isolates, the presence of virulent markers, amino acids (A222, I242, Q253, I256 and S299) and “Serine rich- heptapeptide” indicated the presence of very virulent viruses. The presence of T284A isan indicator of vvIBDVs in local poultry farms. More than 99% similarity of Pakistani isolates with Indian sequences reflects the trans-boundary spread of IBD. In recent studies amino acid, Glutamine (Q) is present at position 221 (as reported in previous studies) rather than Histidine (H) in Pakistani sequences. It is investigated that Glutamic acid (E) is located at position 300 in minor hydrophilic region III of VP2 protein in all reported Pakistani isolates. It is the unique feature of indigenous strains. This study will be useful in understanding the origin and pathotypes of IBDV circulating in Pakistan.