Takahashi Mari, Oguro Shiori, Kato Atsushi, Ito Soma, Tsutsumi Nobuyuki
Nisseiken Co., Ltd., 9-2221-1 Shin-machi, Ome 198-0024, Tokyo, Japan.
Nippon Institute for Biological Science, 9-2221-1 Shin-machi, Ome 198-0024, Tokyo, Japan.
Pathogens. 2024 Dec 23;13(12):1141. doi: 10.3390/pathogens13121141.
Novel antigenic variant strains of the infectious bursal disease virus (IBDV) classified into genogroup A2d have been found in the western part of Japan since 2017. Novel antigenic variant IBDVs now occur in higher frequencies in poultry houses and have been detected in the eastern part of Japan, indicating the spread of IBDVs despite the usual IBDV vaccination. We isolated a novel antigenic variant IBDV, designated as the B2977CE2C3 strain. The B2977CE2C3 strain had two genogroup A2d specific amino acids-lysine and isoleucine, at 221 and 252 aa-along with the other genogroup A2 common amino acids in the projection domains of the VP2 protein corresponding to the virus-neutralizing epitopes and viral pathogenicity. Experimental infection of the B2977CE2C3 strain did not produce any apparent clinical signs in the specific-pathogen-free chickens during the observation period (21 days), but atrophy of the bursa of Fabricius (BF) was apparent. The mean BF to the body weight ratio was 0.35 in negative control chickens at 21 days post-infection (pi) but 0.06 in the B2977CE2C3 infected group. An extremely high copy number of the IBDV genome (>10 copies/µL) was observed in the BF at 3 days pi, while a high copy number of the IBDV genome (>10 copies/µL) was observed in the thymus, spleen cecal tonsil, and bone marrow even though macroscopic lesions were not apparent in these organs.
自2017年以来，在日本西部发现了归类于A2d基因组群的传染性法氏囊病病毒（IBDV）新型抗原变异株。新型抗原变异IBDV目前在家禽舍中出现的频率更高，并且在日本东部也已被检测到，这表明尽管进行了常规的IBDV疫苗接种，IBDV仍在传播。我们分离出一种新型抗原变异IBDV，命名为B2977CE2C3株。B2977CE2C3株在对应病毒中和表位和病毒致病性的VP2蛋白的突出结构域中，除了具有其他A2基因组群常见氨基酸外，在221和252位氨基酸处还有两个A2d基因组群特异性氨基酸——赖氨酸和异亮氨酸。在观察期（21天）内，B2977CE2C3株对无特定病原体鸡的实验性感染未产生任何明显的临床症状，但法氏囊（BF）出现萎缩。感染后21天（pi），阴性对照鸡的平均BF与体重比为0.35，而B2977CE2C3感染组为0.06。感染后3天，在BF中观察到极高拷贝数的IBDV基因组（>10拷贝/µL），而在胸腺、脾脏、盲肠扁桃体和骨髓中也观察到高拷贝数的IBDV基因组（>10拷贝/µL），尽管这些器官中未出现明显的宏观病变。
