| White spot syndrome virus (WSSV) was the most destructive shrimp virus so far. It had spread all over the world since occurred in 1992. This virus brought great economic losses in world shrimp farming every year and has not been controlled completely till today, it was currently the main disease threat to sustainable shrimp farming. In past 10 years, much work has been done about WSSV transmission modes and several routes of infection have been found. These include not only carrier shrimp larvae, other crustaceans (e.g., crabs) and plankton in and around culture ponds, but also bird feces. Shrimp farmers have taken care to culture WSSV-resistant species (e.g., Litopenaeus vannamei), to breed WSSV-free post larvae, to restrict live food inputs, to disinfect inlet water in order to limit horizontal and vertical transmission of WSSV. Despite implementation of measures to reduce transmission, the occurrence of WSSV outbreaks was still very high in mainland China, especially in more northernly regions. This may be due to the fact that some major transmission routes have not yet been discovered.WSSV distribution in shrimp pond system was studied combined with shrimp farming practice by sensitive, crediable detection techniques. Effect and mechanism of rotifer resting eggs in shrimp pond sediments in transmitting WSSV were studied primarily. These study could offer theory information to prevent WSSV transmission effectively. The primary results of the study were as follows:Two pairs of primer were designed for white spot syndrome virus detection. The outer one was for polymerase chain reaction (PCR), the inner one was for producing probe. The results showed that the detection limit of outer primers PCR-electrophorisis was Ipg WSSV DNA, which was lOfg WSSV DNA in PCR-dot blot hybridization; Single inner primers dot blot hybridization could only detect more than Ing WSSV DNA. The sensitivity of PCR-dot blot hybridization was 102 higher than PCR-electrophorisis, 105 higher than single dot blothybridization. The specificity of PCR- dot blot hybridization was confirmed by Southern hybridization. The results showed that PCR-dot blot hybridization was suit for trace WSSV detection.Uracil-DNA glycolsylase (UNO) was used to control carry-over contamination in WSSV DNA detection by PCR . Optimal dUTP and Mg2+ concentrations for this pair of primers were 0.4mM and 2.0mM respectively when UNG was present, the detection limit of WSSV DNA by PCR amplification was Ipg on this condition. UNG made this PCR sensitivity degrade one-tenth. At least lOng WSSV DNA containing dU could be abolished by 0.5U UNG prior to the normal PCR amplification .The negative result was ocurred in WSSV injected Cambarus proclarkii detection with PCR. But, positive results were occurred when the DNA sample was diluted to 10?106 times. Together with the results of DNA probe dot blot hybridization and histopathological section, PCR false negative result could be concluded. The ratio of primer to template for sceessful amplification was 2.43 x]05 ?2.43xl010; The reason and prevent methods for PCR false negative results werediscussed.In 2002, more than 1 000 samples were detected by PCR-DNA probe dot blot hybridization for white spot syndrome virus (WSSV) carrying status. The results showed that 26.6% was WSSV positive in 639 slirimp samples, 18.2% was positive in 77 crab samples, respectively. The WSSV positive ratio was 38.3% in 266 zooplankton samples, and the positive ratio was declined from March to September. Noticeable, the zooplankton positive ratio was still very high after water disinfection. All the 30 snail and shellfish sampbs and 22 filtered seawater samples were WSSV negative. The WSSV positive ratio was 17.6% in 204 mud samples.In 2002, two pen-closing culturing natterns were used to culture Fenneropenaeus chinesis and Litopenaeus vannamei in Rushan shrimp farm. The effects of white spot syndrome prevention were compared. The results showed that the WSSV positive ratio was increased in Fenneropenaeus chinesis culturing process, a...
|
PDF Full Text Request