A Single Mutation of VP2 is Responsible for the Lethality and Antigenicity Differences between Novel Variant and Very Virulent IBDV Strains

Figure 1

Influence of residue 279 of VP2 on the pathogenicity difference between novel variant infectious bursal disease virus (nVarIBDV) and very virulent IBDV (vvIBDV). (a) Amino acid differences between nVarIBDVs (SHG19, 19D38, UPM14322019, and Kagoshima MO 2B-28 strains) and vvIBDVs (HLJ0504, HK46, D6948, and UK661 strains) in the hypervariable region of VP2. nVar, nVarIBDV; vv, vvIBDV. (b) Schematic diagram of the infectious clones of segment A with residue 279 mutation based on the backbone of HLJ0504 or SHG19 strain. (c) Immunofluorescence assay (IFA) of point mutation viruses rHLJ-D279N and rSHG-N279D in DT40 cells with MAb against IBDV VP2 at 24 hr postinfection (hpi). (d) Electron microscopy detection of point mutation viruses rHLJ-D279N and rSHG-N279D in the bursa. The viruses arranged in crystal lattices were marked with arrows. (e) Mean symptomatic index (MSI) of chickens infected with rHLJ0504, rHLJ-D279N, rSHG-N279D, or rSHG19, with a dose of 2.5 × 10⁵ viral RNA copies/200 μl. Treatments with different lowercase letters differ significantly at their confidence level (). (f) Survival curve of the infected chickens within the observation period of 7 days.

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