鳢流行性溃疡综合征病原分离鉴定与病理形态学观察

四川地区养殖的白乌鳢 (Channa argus) 在2021年秋冬阴雨季节频繁发生溃疡性死亡事件。为确定白乌鳢溃疡性疾病的原因，通过临床观察、分离培养、组织学和分子生物学等技术开展了研究。大体病理研究发现，患病鱼主要表现为皮肤脱落并暴露皮下肌肉层，肌肉出现深层溃疡的情况；在光镜下，发现肌肉触片中有直径为10~20 μm的无隔膜分枝状菌丝，通过霉菌分离纯化和ITS基因序列分析，鉴定该病原菌为侵入性丝囊霉菌 (Aphanomyces invadans)。组织病理学显示，在皮肤真皮层和肌肉中的溃疡边缘包围着成熟的肉芽肿，而这些肉芽肿可侵袭至肉眼所观察到的正常肌肉处，对病鱼造成进一步的影响。研究结果表明，此次白乌鳢暴发性死亡的原因是侵入性丝囊霉菌引起的流行性溃疡综合征 (Epizootic Ulcerative Syndrome, EUS)，这是关于白乌鳢流行性溃疡综合征的首次报告。研究结果为侵入性丝囊霉菌的鉴定和临床诊断提供了理论参考，也是侵入性丝囊霉菌宿主进一步扩大的证明。

Epizootic ulcerative syndrome (EUS) in fish: history and current status of understanding

In order to determine the causes of the frequent occurrence of diseases in leucistic northern snakehead (Channa argus) in Sichuan Province of China during the cloudy, rainy autumn and winter, we carried out the reseach by techniques such as clinical observation, isolation and culture, as well as histology and molecular biology, etc.. Generally, the pathological study shows that the main manifestations of the diseased fish were skin peeling, exposing the subcutaneous muscle layer, and the deep ulcer of the muscle. Moreover, non-septate branching fungal hyphae with a diameter of 10–20 µm were observed in squash preparations under light microscopy. The pathogen was identified as invasive Aphanomyces invadans by isolation and purification and ITS sequence analysis. Histopathology reveals that the ulcer edge in the skin dermis and muscle was surrounded by mature granuloma. These granulomas could invade the normal muscles observed by naked eye and caused a further impact on the diseased fish. The findings indicate that the disease was Epizootic Ulcerative Syndrome (EUS), which is the first report of EUS in leucistic C. argus, providing the basic data for the identification and clinical diagnosis of A. invadans. The findings also suggest that a risk of host expansion of this fungus may exist.