Naturally occurring reassortant infectious bursal disease virus in northern China

• A new reassortant IBDV strain (IBD13HeB01) was firstly isolated from northern China.
• Full-length genome of IBD13HeB01 was cloned, sequenced, and analyzed.
• IBD13HeB01 is a segment-reassortment strain with very virulent segment A and attenuated B.
• The virulence of IBD13HeB01 is lower than that of vvIBDV.

Infectious bursal disease virus (IBDV) is a bi-segmented, double-stranded RNA virus that belongs to the genus Avibirnavirus of the family of Birnavirideae. The co-evolution of genome segments is a major evolutionary feature for IBDV. However, in recent years, some strains exhibited markedly different genetic relationships for segments A and B. In this study, we firstly isolated a new type of reassortment IBDV strain named IBD13HeB01 from northern China. The full-length genomes of segments A and B were cloned and identified. Sequence analysis revealed that IBD13HeB01 was a segment-reassortment strain, whose segment A was derived from very virulent strain and segment B from attenuated IBDV. In addition, the virulence of IBD13HeB01 strain was evaluated using SPF chickens. This study is not only beneficial for further understanding of the viral evolution but also suggests the potential risk of application of the live vaccines of IBDV.