Co-infection Of White Spot Syndrome Virus And Taura Syndrome Virus In Litopenaeus Vannamei

Since Litopenaeus vannamei was introduced into our country ,it has become the most popular and highest yield cultured shrimp in recent years. However due to importation of Taura syndrome virus (TSV)-contaminated post larvae or spawners, Taura syndrome is also introduced and devastate the shrimp culture industry. By the outbreak of white spot syndrome virus(WSSV) in 1993 , it has been causing severe damage to the shrimp culture industry. As the culture circumstance deteriorating, the trend of co-infection of TSV and WSSV in Litopenaeus vannamei appears in the process of shrimp culture.The mortality of cultured Litopenaeus vannamei exceeding 90% occur in October, 2003 at a shrimp farm in Jiaozhou, Qingdao. The diseased shrimps are 3-5 cm in length. The reddish hepatopancreas and white spots in the exoskeleton are the typical symptom of the diseased shrimps. The possibility of infection by bacterium or parasites was excluded through observation. The typical white spot syndrome and Taura syndrome symptom are also showed through investigation of epidemiology . In the following experiment, the diseased shrimps are researched from histopathology .In order to find the agents, fluorescence antibody technique (IFAT) and polymerase chain reaction (PCR) technique and virus purification technique are also used.Histologically the general body surface shows evident pathological changes as necrotic lesions .The cells of hepatopancreas and midgut display an increased eosinophilia of the cytoplasm and pyknosis nuclei. In the cells of gill tumescent nuclei are found. Under the microscope , the virus particles of WSSV are found in the cell of gill. The agents are not found in the cell of hepatopancreas.discontinuous sucrose gradient technique is designed to purify the agents. Between the sucrose gradient of 30% and 35% was the band of TSV; Between the sucrose gradient of 46 and 52% was the band of WSSV.Through immuno-fluorescence antibody technique (IFAT) and polymerase chain reaction (PCR), white spot syndrome virus (WSSV) wasdetected in the gills of the shrimps. In the same sample, Taura syndrome virus (TSV) was also detected through Reverse-transcription polymerase chain reaction (RT-PCR). It can conclude that it was the co-infection of the two viruses which caused the high mortality of the shrimps. Multiplex polymerase chain reaction is also designed in order to detect WSSV and TSV more rapidly and accurately.