Identification and Pathogenicity Evaluation of a Novel Reassortant Infectious Bursal Disease Virus (Genotype A2dB3)

Abstract

Infectious bursal disease virus (IBDV) is a non-enveloped, bi-segmented double-stranded RNA virus and the causative agent of a poultry immunosuppressive disease known as infectious bursal disease (IBD). The novel variant IBDV (nVarIBDV) recently posed a great threat to the development of the poultry industry. In this study, we identified a novel segment-reassortant IBDV strain, IBDV-JS19-14701 (Genotype A2dB3). Phylogenic analysis showed that Segments A and B of IBDV-JS19-14701 were derived from emerging nVarIBDV (Genotype A2dB1) and long-prevalent HLJ0504-like strains (Genotype A3B3) in China, respectively. The pathogenicity of IBDV-JS19-14701 was further evaluated via animal experiments. IBDV-JS19-14701 exhibited a similar virulence to chickens with the nVarIBDV. The identification of this reassortment event is beneficial for understanding the epidemiology of nVarIBDV and will contribute to the efficient prevention and control of IBD.

Keywords: genome; infectious bursal disease virus; novel variant strain; pathogenicity; segment reassortment.

Figure 1

Phylogenetic analysis of the nucleotide sequences encoding the polyproteins (a) and VP1 (b). The trees were generated by the neighbor-joining method with MEGA6 software. Trees were drawn to scale, with branch lengths measured in the number of substitutions per site. Only branches supported by a bootstrap value above 50% were displayed. The genogroup and corresponding phenotype for each branch was marked. The segment-reassortant strain detected in this study (IBDV-JS19-14701) was highlighted with a solid circle.

Figure 2

Identification of co-infection by restriction enzyme digestion analysis. (a) A part of the nucleotide alignment report showing the presence or absence of the Hind III restriction enzyme site (bp 2188–bp 2193) in Segment A. An asterisk indicates a residue identical to the IBDV-JS19-14701 strain. The shaded area indicates the presence of a Hind III restriction site; (b) total RNA of IBDV-JS19-14701, SHG19, or HLJ0504 was extracted and subjected to RT-PCR, respectively. The RT-PCR products (bp 1421–bp 3170 of Segment A, 1749 bp) were then subjected to Hind III digestion.

Figure 3

Pathogenicity evaluation of the reassortant strain IBDV-JS19-14701. (a) B/BW ratio at seven days post-infection (* p < 0.05); (b) Representative hematoxylin and eosin (H&E) staining (scale bars, 200 μm) and immunohistochemistry (IHC) staining (scale bars, 50 μm) of IBDV VP2 protein in the bursal tissues harvested at seven days post-infection.