Pathogenic mechanisms and molecular features of a novel UL2 gene-deficient duck enteritis virus endemic to China

Duck enteritis virus (DEV) was identified as the etiological agent responsible for an outbreak of morbidity and mortality in adult ducks on a farm in Jiangsu, China. Diagnostic approaches confirmed that the outbreak was caused by the highly pathogenic DEV-JS2024 isolate. The clinical progression of the disease, characterized by lethargy, anorexia, ocular discharge, and high mortality, was accompanied by extensive hemorrhagic lesions in critical organs such as the liver, spleen, lungs, and bursa of Fabricius, consistent with known signs of DEV infection. Genomic analysis of DEV-JS2024 revealed a 45% G+C content and 76 open reading frames. BLASTn analysis revealed that the genome of DEV-JS2024 shares the highest sequence similarity with the Chinese virulent strain CV and the DEV attenuated vaccine strain C-KCE in the database. These results indicate a close genetic relationship between DEV-JS2024 and both the virulent and attenuated strains, suggesting potential similarities in their genomic architecture. Comparative genomic analysis identified 28 nucleotide mutations, including 15 non-synonymous mutations potentially related to virulence factors. The study also highlighted the first reported 528 base pairs deletion in the UL2 gene of a virulent strain, challenging its utility as a marker for distinguishing virulent from attenuated strains. Phylogenetic analysis suggested that DEV-JS2024 may result from recombination between the vaccine and virulent strains, further complicating our understanding of DEV pathogenicity. This study provides new insights into the molecular evolution of DEV and stresses the importance of continued genomic surveillance to enhance vaccine development and control measures for duck plague.本研究确认，鸭肠炎病毒（Duck enteritis virus, DEV）为中国江苏某养殖场成年鸭暴发高发病率与高死亡率疫情的致病原。经诊断方法验证，此次疫情由高致病性分离株DEV-JS2024引发。该疾病的临床特征为精神沉郁、食欲废绝、眼部分泌物增多及高死亡率，同时可见肝脏、脾脏、肺脏及法氏囊等关键器官的广泛性出血性病变，与已报道的DEV感染症状一致。对DEV-JS2024的基因组分析显示，其G+C含量为45%，共包含76个开放阅读框（open reading frames）。BLASTn分析结果表明，DEV-JS2024的基因组与数据库中中国强毒株CV及DEV减毒疫苗株C-KCE的序列相似性最高。上述结果提示，DEV-JS2024与上述强毒株及减毒株均存在紧密的遗传亲缘关系，表明三者的基因组结构可能具有相似性。比较基因组分析共鉴定出28个核苷酸突变，其中包括15个可能与毒力因子相关的非同义突变。本研究同时首次在强毒株的UL2基因中报道了528 bp的缺失，这一发现对该缺失作为区分强毒株与减毒株的分子标记的实用性提出了挑战。系统发育分析结果显示，DEV-JS2024可能由疫苗株与强毒株重组演化而来，这进一步使我们对DEV致病性的认知变得更为复杂。本研究为DEV的分子演化研究提供了新的视角，并强调了持续开展基因组监测的重要性，以助力鸭瘟的疫苗研发与防控措施优化。