Huang Yuanling, Shu Gang, Huang Cong, Han Jingyi, Li Jia, Chen Hongjun, Chen Zongyan
College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China.
Shanghai Veterinary Research Institute, Chinese Academy of Agricultral Science (CAAS), Shanghai, China.
Front Microbiol. 2023 Mar 17;13:1039259. doi: 10.3389/fmicb.2022.1039259. eCollection 2022.
Infectious bursal disease (IBD) is a highly epidemic and immunosuppressive disease of 3- to 6-week-old chicks caused by infectious bursal disease virus (IBDV). Since 2017, there has been a notable increase in the isolation rates of novel variant IBDV strains in China, of which characteristic amino acid residues were different from those of early antigen variants. In this study, one IBDV strain was isolated from a farm with suspected IBD outbreak in Shandong Province, China, which was designated LY21/2. The strain LY21/2 could replicate in MC38 cells with previous culture adaption in SPF chick embryos. Phylogenetic analysis revealed that LY21/2 formed one branch with novel variant IBDVs and shared 96.8-98.6% nucleotide sequence identity with them. Moreover, LY21/2 serving as the major parent underwent the recombination event of a variant strain (19D69), while the minor parent was a very virulent strain (Harbin-1). SPF chicks inoculated with LY21/2 showed no gross clinic symptom, whereas bursal atrophy was exhibited and apoptosis was occurred in 55.21% of bursal cells. The results of histopathology and immunohistochemical staining showed that lymphocyte depletion and connective tissue hyperplasia and IBDV antigen-positive cells were observed in the bursa of LY21/2-infected chicks. Besides, DNA fragmentation was detected in the LY21/2-infected bursal tissue section by TUNEL assay. Collectivtely, these data presented analysis and evaluation of the genetic characteristics and pathogenicity of a novel variant IBDV strain. This study may help in the development of biosafety strategies for the prevention and control of IBDV in poultry.
传染性法氏囊病（IBD）是由传染性法氏囊病病毒（IBDV）引起的3至6周龄雏鸡的一种高度流行且具有免疫抑制性的疾病。自2017年以来，中国新型变异IBDV毒株的分离率显著增加，其特征性氨基酸残基与早期抗原变异株不同。在本研究中，从中国山东省一个疑似IBD爆发的养殖场分离出一株IBDV毒株，命名为LY21/2。LY21/2毒株在经SPF鸡胚预先适应培养后可在MC38细胞中复制。系统发育分析表明，LY21/2与新型变异IBDV形成一个分支，与它们的核苷酸序列同一性为96.8%至98.6%。此外，LY21/2作为主要亲本经历了一个变异株（19D69）的重组事件，而次要亲本是一个超强毒株（哈尔滨-1）。接种LY21/2的SPF雏鸡未表现出明显的临床症状，但出现了法氏囊萎缩，且55.21%的法氏囊细胞发生了凋亡。组织病理学和免疫组化染色结果显示，在LY21/2感染雏鸡的法氏囊中观察到淋巴细胞耗竭、结缔组织增生以及IBDV抗原阳性细胞。此外，通过TUNEL检测在LY21/2感染的法氏囊组织切片中检测到DNA片段化。总体而言，这些数据展示了对一株新型变异IBDV毒株的遗传特征和致病性的分析与评估。本研究可能有助于制定家禽IBDV预防和控制的生物安全策略。
