Molecular and in vivo Characterization of an Iranian Infectious Bursal Disease Virus Containing a Mixed Virus Population

BACKGROUND: Infectious bursal disease (IBD) is a highly contagious immunosuppressive disease of young chickens caused by infectious bursal disease virus (IBDV). IBDV consists of a two-segmented double-stranded RNA genome which can easily undergo genomic recombination or reassortment during mixed infections. OBJECTIVES: The objectives of this study were to characterize a previously identified Iranian IBDV strain (JRMP29IR) in specific-pathogen-free (SPF) chickens, evaluate the presence of a mixed and/or reassortant virus population in this strain, and examine the frequency of genomic recombination and reassortment in publicly available IBDV genomes through bioinformatics. METHODS: The SPF chickens were challenged with the JRMP29IR strain via oral and intraocular routes. Bursal tissues were extracted for histopathological evaluation and reverse transcription-polymerase chain reaction (RT-PCR) followed by Sanger sequencing. Putative recombinations and reassortments were evaluated using the Recombination Detection Program 5. RESULTS: Through genomic sequencing of the viruses from the bursas of infected chickens, the JRMP29IR strain was found to contain viruses from the classic, variant and very virulent IBDV genotypes. Through bioinformatics, numerous putative recombination and reassortment events were identified that naturally occured throughout the IBDV genome. CONCLUSIONS: Parental JRMP29IR appears to be derived from a flock undergoing a mixed IBDV infection. High frequency of recombination and reassortment among IBDVs suggests that these events are evolutionarily beneficial for the virus.