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.

中文翻译：

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传染性法氏囊病病毒的ITA基因型分离株（G6）的体内致病性比较研究。

最近，在接种IBD的意大利肉鸡中发现了一种新的传染性法氏囊病病毒（IBDV）基因型，名为ITA。基因组表征显示ITA是一种遗传上不同的IBDV，根据最近提出的IBDV分类，它属于基因组6。当前可获得的临床数据不允许对ITA-IBDV分离株的致病性程度进行任何定义。在本研究中，通过口服接种无特定病原体（SPF）的鸡进行了致病性试验。将鸟圈养在家禽隔离器中，并在35日龄时接种ITA-IBDV分离株（35只鸟）或作为对照的属于G1a基因组的菌株（35只鸟）。对照鸟（25只鸟）在上下文中用无菌水模拟接种。每天观察鸟类的临床体征，并在0、7、14时观察 接种后21和28天（dpi）取血用于IBDV抗体检测。在2、4、7、14、21和28 dpi时，对每只接种组的五只鸟和对照组的三只鸟实施安乐死并进行尸检。计算法氏囊：体重和胸腺：体重比。分别根据淋巴样坏死和/或耗竭或皮质萎缩对滑囊和胸腺的微观病变进行评分。两种病毒均诱导出亚临床病程，因为即使在存在典型的IBDV肉眼和镜下病变的情况下，研究期间也未记录到临床体征或死亡率。ITA-IBDV接种后，以法氏囊：体重比衡量的法氏囊损伤更为明显和早熟。滑囊的组织病理学评分，表明淋巴样快速耗竭，证实了ITA-IBDV毒株在该器官中的侵袭性。这项研究表明，尽管所测试的ITA-IBDV菌株会在亚临床病程中引起感染，但它会对淋巴组织造成严重损害。因此，其在禽类中的流通可能对家禽业构成威胁，并可能危及生产周期的成功。