Novel Antigenic Variant Infectious Bursal Disease Virus Outbreaks in Japan from 2014 to 2023 and Characterization of an Isolate from Chicken

Figures

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  Figure 1. Phylogenic tree of IBDV B2977CE2C3. A phylogenic tree based on the segment A sequence of the IBDV is shown. The IBDV B2977CE2C3 strain is shown in bold with a star. Relevant sequences of IBDV strains collected from GenBank are shown with the DNA database accession number. Seven genogroups, A1 to A7, of the IBDV strains classified using the Maximum Likelihood method are shown. Sub-genogroups (A2a, A2b, A2c, and A2d) further classified from genogroup A2 are also shown.

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  Figure 2. Amino acid substitutions at putative antigenic sites on VP2 projection domains of IBDV. Four P domains, PBC, PDE, PFG, and PHI, possessing the putative antigenic sites of VP2, are indicated on the top with the amino acid number. Deduced amino acid sequences in the projection domains of IBDV B2977CE2C3 are compared with those of other strains in different genogroups (A1, A2, A3, A4, A5, A6, and A7). Relevant sequences of IBDV strains were collected from GenBank. A common amino acid found in a genogroup is shown in red. An exceptional amino acid that is not found in other strains within a genogroup is shown in green. Two amino acids (221K and 252I) commonly found in the sub-genogroup A2d strain are shown in the box.

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  Figure 3. Effects of the infection of novel antigenic IBDV B2977CE2C3 strain on BW and BF. The increase in body weight (A) and the body weight/BF weight ratio (B) were examined in IBDV B2977CE2C3 infected (blue) and mock-infected chicken (orange) groups. All chickens in both groups were weighed before inoculation (day 0). Six chickens of each group were weighed at 3, 7, 14, and 21 days post-inoculation (pi) and were then sacrificed. The BF was isolated from the sacrificed chickens, and its mass was weighed. The mean value at each measurement point is shown with a bar graph. Symbols * and *** indicate p < 0.05 and p < 0.001, respectively, calculated using an unpaired t-test between the B2977CE2C3 strain-infected and mock-infected groups. Deviation (+/− SD) is shown with error bars on the bar graph.

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  Figure 4. Viral genome copy number in the lymphoid tissues. BF (blue), thymus (orange), spleen (gray), cecal tonsil (yellow), and bone marrow (light blue) were taken from both infected and mock-infected chicken groups at 3, 7, 14, and 21 days post-inoculation (pi). The viral genome copy number in 10% tissue homogenate was measured via quantitative RT-PCR using the quantity known standard as a reference. The vertical axis indicates the natural logarithm of copy number (Log10 [copy number]). The horizontal axis indicates days after the B2977CE2C3 strain infection or the mock infection. The mean genome copy number at each measurement point is shown as a bar graph. Deviation (+/− SD) is shown on the mean bar graph.

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  Figure 5. Anti-IBDV serum titers of IBDV B2977CE2C3 infected chickens. The vertical axis indicates anti-IBDV antibody ELISA titers (S/N). The horizontal axis indicates days post-infection. Six sera are shown individually by open circles. The closed circle indicates the mean anti-IBDV antibody ELISA titer. Deviation (+/− SD) is shown on the closed circle representing the mean value. The cutoff value is 0.2. Since none of the samples at 3 days post-infection produced an anti-IBDV ELISA value (S/P), an open circle is representatively shown at 0.0 on the vertical axis.