Department of Veterinary Medical Sciences, University of Bologna, Ozzano dell'Emilia (BO), Italy.
CEVA Salute Animale, Agrate Brianza (MB), Italy.
Transbound Emerg Dis. 2020 Mar;67(2):1025-1031. doi: 10.1111/tbed.13421. Epub 2019 Nov 24.
Recently, a new genotype of infectious bursal disease virus (IBDV), named ITA, was detected in IBD-vaccinated Italian broilers. Genome characterization revealed ITA to be a genetically different IBDV, belonging to genogroup 6 according to a recently proposed IBDV classification. The currently available clinical data do not allow any definition of the degree of pathogenicity of the ITA-IBDV isolates. In the present study, a pathogenicity trial was conducted by the oral inoculation of specific-pathogen-free (SPF) chickens. Birds were housed in poultry isolators and inoculated at 35 days of age with an ITA-IBDV isolate (35 birds) or a strain belonging to the G1a genogroup as a comparison (35 birds). Control birds (25 birds) were contextually mock-inoculated with sterile water. Birds were observed daily for clinical signs and at 0, 7, 14, 21 and 28 days post-inoculation (dpi) were bled for IBDV antibody detection. At 2, 4, 7, 14, 21 and 28 dpi, five birds from each of the inoculated groups, and three from the control group, were euthanized and subjected to a post-mortem examination; the bursa:body weight and thymus:body weight ratios were calculated. Microscopic lesions of the bursa and thymus were scored on the basis of lymphoid necrosis and/or depletion or cortex atrophy, respectively. Both viruses induced a subclinical course of disease, as neither clinical signs nor mortality were recorded during the study, even in the presence of typical IBDV gross and microscopic lesions. Bursal damage, measured by the bursa:body weight ratio, was more noticeable and precocious after ITA-IBDV inoculation. Histopathology scores of the bursa, indicative of rapid lymphoid depletion, confirmed the aggressiveness of the ITA-IBDV strain in this organ. This study showed that, although the ITA-IBDV strain tested causes infection with a subclinical course, it induces severe damage to lymphoid tissues. Therefore, its circulation in birds might be a threat for the poultry industry and may jeopardize the success of the production cycle.
最近，一种新型传染性囊病病毒（IBDV）的基因型，命名为 ITA，在接种 IBD 疫苗的意大利肉鸡中被检测到。基因组特征表明，ITA 是一种具有遗传差异的 IBDV，根据最近提出的 IBDV 分类，属于基因 6 组。目前的临床数据尚无法确定 ITA-IBDV 分离株的致病程度。在本研究中，通过口服接种 SPF 鸡进行了致病性试验。鸡被安置在禽隔离器中，在 35 日龄时用 ITA-IBDV 分离株（35 只鸡）或属于 G1a 基因组的株系（35 只鸡）进行接种。对照鸡（25 只鸡）用无菌水进行模拟接种。每天观察鸡的临床症状，并在接种后 0、7、14、21 和 28 天（dpi）采血检测 IBDV 抗体。在 2、4、7、14、21 和 28 dpi 时，从每个接种组中选择 5 只鸡，从对照组中选择 3 只鸡进行安乐死，并进行剖检；计算法氏囊：体重和胸腺：体重比。根据淋巴细胞坏死和/或耗竭或皮质萎缩，分别对法氏囊和胸腺的显微镜下病变进行评分。两种病毒均引起亚临床疾病，因为在研究期间既没有记录临床症状也没有记录死亡率，即使存在典型的 IBDV 大体和显微镜下病变。ITA-IBDV 接种后，法氏囊：体重比测量的法氏囊损伤更明显且更早。法氏囊的组织病理学评分，表明淋巴细胞迅速耗竭，证实了 ITA-IBDV 株在该器官中的侵袭性。本研究表明，尽管测试的 ITA-IBDV 株引起亚临床感染，但它会引起淋巴组织的严重损伤。因此，其在禽类中的传播可能对家禽业构成威胁，并可能危及生产周期的成功。
