1996年中国对虾暴发性流行病病毒病原研究

STUDY OF THE VIRAL AGENT CAUSING EPIZOOTIC IN CHINESE CULTIVATED PENAEID SHRIMP PENAEUS CHINENSIS IN 1996

１９９６年６月至８月，青岛地区养殖的中国对虾（Ｐｅｎａｅｕｓｃｈｉｎｅｎｓｉｓ）大面积暴发流行病，死亡率达９０％以上。发病对虾典型表征为甲壳白斑。病虾鳃组织匀浆滤液经微孔滤膜过滤除菌后，注射给健康对虾进行人工感染试验，９天内累计死亡率达１００％，发病症状及体征与自然发病对虾相似。电镜下自然发病对虾鳃、胃、头胸甲下表皮、淋巴样器官、触角腺等组织细胞核内发现大量杆状病毒，未见包涵体；人工感染对虾相同组织中可见大量同样病毒。切片中病毒粒子有包膜，完整毒粒大小为１２５±７６×３４５±１６ｎｍ，核衣壳为８５±６５×２９５ｎｍ。核质内可见不同成熟阶段的病毒形态，部分毒粒一端有突出的乳头状结构。经氯化铯密度梯度纯化后，包膜全部丢失。负染标本显示，核衣壳呈杆状，螺旋对称，大小为８０±１３×３８０±２４３ｎｍ，衣壳由１３～１６条螺旋带构成。研究结果表明，该病毒致病及形态特征与已报道的白斑征杆状病毒（Ｗｈｉｔｅｓｐｏｔｓｙｎｄｒｏｍｅｂａｃｕｌｏｖｉｒｕｓ，ＷＳＢＶ）相似，是１９９６年中国对虾暴发性流行病的主要病原。本文称之为“中国对虾非包涵体型杆状病毒（Ｐｅｎｅａｕｓｃｈｉｎｅｎｓｉｓｎｏｎ－ｏｃｌｕｄｅｄｂａｃｕｌｏ?

Serious epizootic causing high mortality (90%) among cultivated Penaeus chinensis occurred in Qingdao Prefecture, East China, between June and August in 1996. Typical external sign of the disease was white spots on the carapace. Similar epizootic was firstly observed in the same prefecture in 1993. Reinfection tests by injection of filtered gill homogenate from diseased shrimps ( P. chinensis ) demonstrated that the causative agent was highly virulent with 100% of cumulative mortalities within 9 days. A non-occluded nuclear bacilliform virus was mostly found by electron microscopy in the gill, cuticular epidermis under the exoskeleton, stomach, lymphoid organ and other tissues of ectodermal and mesodermal origin from naturally diseased shrimps. White spots on the carapace and similar viruses were also found from the artificially infected shrimps. The virion was enveloped with a mean size of 125±7.6×345± 16nm. The average size of enveloped nucleocapsid was 85±6.5×295nm. Sometimes, a nipple-like appendage could be found protruding from one extremity of the virion. Viruses at different stages of assembly were usually found in the nucleoplasm. Envelopes were all lost after purification from cesium chloride density gradient ultracentrifugation. The cylindrical nucleocapsid in negatively stained preparations was 80±13nm×380±24nm with 13-16 stripes. Based on its pathogenic and morphological characteristics, this virus should belong to the White Spot Baculoviruses (WSBVs) and is proved to be the major causative agent of the epizootic. To differ from the names of other isolates of WSBVs from P. monodon and P. japonicus in Thailand,Taiwan and Japan, this virus is temporally named as Penaeus chinensis non-occluded baculovirus (PcNOBV) representing the strain isolated from cultivated P. chinensis in China.