Wang Yifan, Xu Liwen, Ma Weixiang, Sun Heng, Huang Zengchao, Cai Shuanghu, Jian Jichang, Huang Yucong
Guangdong Provincial Key Laboratory of Pathogenic Biology and Epidemiology for Aquatic Economic Animals & Key Laboratory of Control for Diseases of Aquatic Economic Animals of Guangdong Higher Education Institutes, Fisheries College of Guangdong Ocean University, Zhanjiang, China.
Key Laboratory of South China Sea Fishery Resources Exploitation & Utilization, South China Sea Fisheries Research Institute of Chinese Academy of Fishery Sciences, Ministry of Agriculture and Rural Affairs, Guangzhou, China.
J Fish Dis. 2022 Feb;45(2):277-287. doi: 10.1111/jfd.13553. Epub 2021 Nov 14.
In December 2019, a mass mortality among cultured Murray cod (Maccullochella peelii peelii) fry occurred on a freshwater farm located at Foshan city of Guangdong province, China. The cumulative mortality was up to 45% within 15 days. The diseased fish showed clinical signs, including abnormal swimming behaviour, loss of appetite and dark body colouration before mass mortality. Samples of brain and retina tissues were collected from affected fish and subjected to reverse transcriptase polymerase chain reaction detection and virus isolation in cell culture. Approximately 430 bp product was detected from the brain and retina tissues and culture supernatant of betanodavirus-infected SSN-1 cells. The typical cytopathic effect of betanodavirus infection, which is characterized by vacuolation, was observed in SSN-1 cells at three days after inoculating with the tissue filtrate of diseased Murry cod fry, and the TCID of the infected SSN-1 cell supernatant was 10 . Histopathological examinations revealed vacuolation and necrosis in the brain and retina of naturally and experimentally infected Murray cod fry. Electron microscopic observation also showed the aggregation of numerous spherical, non-enveloped viral particles measuring 22-28 nm in diameter in the cytoplasm of betanodavirus-infected SSN-1 cells. Sequence and phylogenetic analysis based on RdRp and Cp genes further indicated that the betanodavirus isolated from Murray cod belonged to the RGNNV genotype. Much higher mortality was obtained in challenged Murray cod fry compared with the controls through immersion challenge. This study is the first report of the natural infection of betanodavirus in freshwater fish in China.
2019年12月，中国广东省佛山市一家淡水养殖场养殖的墨瑞鳕（Maccullochella peelii peelii）鱼苗发生大规模死亡。15天内累计死亡率高达45%。患病鱼苗在大规模死亡前出现了包括异常游泳行为、食欲不振和体色变黑等临床症状。从患病鱼苗采集脑和视网膜组织样本，进行逆转录聚合酶链反应检测及细胞培养病毒分离。在受β-诺达病毒感染的SSN-1细胞的脑、视网膜组织及培养上清液中检测到约430bp的产物。用患病墨瑞鳕鱼苗的组织滤液接种SSN-1细胞三天后，观察到β-诺达病毒感染典型的细胞病变效应，其特征为空泡化，感染的SSN-1细胞上清液的半数组织培养感染剂量（TCID）为10 。组织病理学检查显示，自然感染和实验感染的墨瑞鳕鱼苗的脑和视网膜有空泡化和坏死。电子显微镜观察还显示，在受β-诺达病毒感染的SSN-1细胞的细胞质中有大量直径为22 - 28nm的球形、无包膜病毒颗粒聚集。基于RNA依赖的RNA聚合酶（RdRp）和衣壳蛋白（Cp）基因的序列及系统发育分析进一步表明，从墨瑞鳕分离的β-诺达病毒属于红鳍东方鲀神经坏死病毒（RGNNV）基因型。通过浸泡攻毒，攻毒的墨瑞鳕鱼苗的死亡率远高于对照组。本研究是中国淡水鱼中β-诺达病毒自然感染的首次报道。
