| White spot syndrome virus (WSSV) first appeared in1992in Taiwan, it’s a rod-shaped double-stranded DNA virus without inclusion body and has been highly pathogenic for different varieties of shrimps. WSSV caused acute fatal infectious diseases and huge economic losses in the global shrimp farming industry, and this situation was particularly serious in China. WSSV has wide geographical distribution, wide range of popular and strong infectivity, and the incidence rises with the development of the shrimp farming industry. Several outbreaks of shrimp disease happened frequently in coastal areas of Jiangsu and it caused mass mortalities of cultured Exopalamon carincauda since2007.The investigation of horizontal transmission routes on WSSV from some coastal areas of Jiangsu has conducted in the study from July2012to April2013. Anest-PCR has been performed to detect the WSSV from live shrimp, fresh chilled bait and the environmental samples such as copepod, algae, mud and water. The investigation showed that80%of the shrimp samples were infected with WSSV, and there were massive mortalities in some pathogentic ponds and the mortality spreaded from some areas to adjacent areas. The incidence and mortality of September and October were higher than the other months in2012. The positive ratio of WSSV of crab was relatively high, and some samples of fresh chilled bait, copepod and algae carried a certain percentage of WSSV and the wild shrimp and crab also carried WSSV. The result showed that Exopalamon carincauda, crab and bait played an important role and the role of copepod and microalgae could not be ignored in the process of WSSV infecting Exopalamon carincauda, but the role of mud and water remained to be elucidated. Either shrimp, or crab, bait, copepods and microalgae may become sources of transmission of WSS after infected with WSSV.The investigation of vertical transmission route on WSSV has also conducted. During the spawning period of Exopalamon carincauda, we collected the broodstocks in two tranches. The eggs of every broodstock were observed by perspective microscope and got related information on stages of embryonic development. After extracting DNA in the tissue and eggs, a nest-PCR has been performed to detect WSSV from the samples. The investigation showed that most of the eggs were in blastocyst stage, gastrula stage, nauplii stage and zoea larvae stage.53%of the broodstocks and33%of the eggs were infected with WSSV by PCR.Some samples of the eggs in blastocyst stage, gastrula stage, nauplii stage and zoea larvae stage were infected with WSSV. Because the eggs in blastocyst stage, gastrula stage, nauplii stage didn’t start to feed, WSSV could not be spread by mouth, and the possibility of the surface of the eggs carrying WSSV was excluded at the same time, so the possibility that WSSV existing in the eggs originated from the external environment was excluded finally. The investigation of vertical transmission routes showed that WSSV existing in the eggs originated from the broodstocks, and the route of vertical transmission of WSSV may be present, but the further study would be needed to confirm the conclusion.In the study, we infected Exopalamon carincauda with WSSV artificially, and the enzyme avtivity for four immune-enzymes(ACP, AKP, SOD, POD) was investigated at0thh,6thh,12thh,24thh,36thh,48thh,60thh,72thg after the shrimps was infected with WSSV. The results showed that the enzyme avtivity of ACP, AKP, SOD and POD had certain trends and characteristics within72hours after the shrimps was infected with WSSV:the avtivity of ACP and AKP increased to the highest enzyme avtivity at36th h and48th h; the avtivity of SOD and POD increased to the highest enzyme avtivity at60th h and6th h; ACP, AKP, SOD and POD were sensitive to pathogenic reaction, so that they could provide technical basis to prevent and control the WSSV infection of Exopalamon carincauda.According to the conclusions obtained by the investigation, combining with the Exopalamon carincauda farming industry in coastal areas of Jiangsu, we propose the prevention and control measures against outbreak of WSSV in Jiangsu. |
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