罗氏沼虾肌肉白浊病的病原和组织病理

Pathogen and histopathology of muscle whitish disease in Macrobrachium rosenbergii

对患肌肉白浊病的罗氏沼虾进行细菌分离、寄生虫检查、组织病理观察以及虾池的水质分析和疾病的流行病学调查,排除了细菌、寄生虫以及水质环境因素造成该病的可能性,并发现病症多发生在体长0 8～3cm的幼虾中,而体长3cm以上的虾病症明显减轻。病虾的显微和亚显微组织病理观察发现,病虾腹部白浊的肌肉组织肌纤维肌浆内存在嗜碱性包涵体,肝胰腺、血细胞、心脏和鳃组织细胞胞浆内也有嗜碱性包涵体出现,包涵体内有大量以晶格状排列、无囊膜的二十面体球状病毒颗粒,直径为(23.6±3.8)nm(n=40)。在包涵体外的胞浆内,尤其在白浊肌肉组织肌纤维肌浆内也分布有大量病毒。心脏和鳃组织出现不同程度的变性,肌肉组织、肝胰腺、血细胞除变性外还出现坏死;肌肉组织病变尤为严重,肌肉白浊症状是肌肉组织变性、坏死的结果。将病虾白浊肌肉组织以口服方式感染健康虾,健康虾出现与自然发病虾一样的症状,发病率和死亡率亦与自然感染病虾相近,表明上述二十面体球状病毒是罗氏沼虾肌肉白浊病的病原。

An investigation on the outbreaks of muscle whitish disease in giant freshwater prawn Macrobrachium rosenbergii has been conducted from spring to summer since 2000 in the culture farms around the suburbs of Shanghai City and Wujiang City of Jiangsu Province. The disease usually outbroke from March to August when the prawns were just during the seeding phase and larvae culturing phase. And the muscle whitish usually happened to the larvae with body length at from 0.8 cm to 3 cm,while over 3.0 cm of body length the diseased degree was allayed. The diseased prawns are observed under light and electron microscopes in terms of histopathology and the results show that there are many basophilic inclusion bodies within the sarcoplasm of muscle cells in the abdominal whitish muscle tissues, and the basophilic inclusion bodies also appear in the cytoplasm of hepatopancreas,blood cells ,heart and gill. The cytoplasmic inclusion bodies contain massive nonenveloped viruses which show icosahedra and array as crystalshaped at the mean size of (23.6±3.8) nm (n=40) in diameter. The viruses also appear in the cytoplasm outside the inclusion bodies, especially in the sarcoplasm of muscle cells. The heart and gill tissues degenerate to some extent and the muscle, hepatopancreas and blood cells are necrotic besides the degeneration. The muscle tissue is the most severe in histopathological change, and the symptom of abdominal whitish muscle is due to the degeneration and necrosis in myofibril. The artificial infection experiment was conducted by oral administration of whitish muscle tissue of diseased prawns to health prawns. The results show that the viruses found in diseased prawns are the pathogen of the muscle whitish disease of M. rosenbergii.