我国养殖大菱鲆病毒性红体病及其流行情况调查

Investigation of pathogen and epidemiology of a novel disease, ‘Viral reddish body syndrome’, among farmed Scophthalmus maximus in China

大菱鲆病毒性红体病(Viral reddish body syndrome, VRBS)是一种新发现的感染我国养殖大菱鲆的流行性疾病.本文描述了病鱼的外观症状和解剖病理特征,报道了该病的病原及疾病流行情况调查结果.外观检查发现,病鱼的体表无明显损伤,但腹面沿脊椎骨附近皮下淤血、发红,鳍及鳍基部充血、发红;病鱼贫血,血液凝固性差;肾脏肿大,呈灰白色.组织病理学研究显示病鱼脾组织中存在大量肥大细胞,电镜切片中可见大量平均直径约125 nm的二十面体病毒粒子,即大菱鲆红体病虹彩病毒(Turbot reddish body iridovirus, TRBIV).将过滤除菌的含TRBIV的病鱼脾组织匀浆液,经腹腔注射进行人工感染,感染鱼在3周内的累积死亡率达85.7%,死亡大菱鲆表现出腹面和鳍边发红等外观症状,并在感染鱼脾组织切片中观察到大量同样的病毒粒子,由此证实TRBIV是我国养殖大菱鲆病毒性红体病的病原.疾病流行情况调查显示,该病多在养成期大菱鲆中流行,高发季节为每年的8～12月.

A novel infectious disease affecting farmed turbot, Scophthalmus maximus, was described. This disease named as ‘Viral reddish body syndrome’ (VRBS) has caused severe mortalities of farmed turbot and led to serious economic losses in China. Affected fish generally lacked external lesions. The only consistent abnormalities were pale gills with local haemorrhages, petechial haemorrhages in fins and fin bases, especially haemorrhages in muscle and skin. Anaemia, pallor and enlarged kidneys were usually observed in severe affected fish. Investigations showed that the aetiological agent was neither parasite nor bacteria. By light microscope, many enlarged cells were observed in the spleen of diseased turbot. Numerous viral particles 125 nm in diameter with icosahedral in symmetry were detected by transmission electron microscopic (TEM) examination in the cytoplasm of diseased turbot. The virus is subsequently identified as Turbot reddish body iridovirus (TRBIV). Intraperitoneal inoculation of the filtrate (450 nm) from spleen homogenate of VRBS fish to turbot juveniles induced 85.7% of cumulative mortalities within 3 weeks, while no turbot died in control group. Moribund fish showed similar clinical signs as VRBS fish and numerous TRBIV particles were observed in the spleen by TEM. This experiment proved that TRBIV is the causative pathogen of VRBS. Further investigations of epidemiology suggested that juveniles, 10~20 cm in length or 100~400 g in weight, be most easily affected by VRBS and the peak prevalent seasons of the disease be from August to December.