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Objective To evaluate the effects of the project of ditching for drain on Oncomelania hupensis snail control and flood prevention security and explore the optimal engineering design plan in Dongting Lake region. Methods A retrospective study was performed on the previous studies about the project of ditching for drain. The reference values of project indices were determined. The outside levee of Nanhu New Distinct of Yueyang City in Dongting Lake region was selected as the study area , and the cross section of marshland perpendicular to the center line of the levee was extracted to research. According to the situa?tions of various water levels,a dynamic simulation was performed on the effect and security of the project of ditching for drain through the software FLAC3D. Results The retrospective study showed that the project would be effective when the relatively subsoil water level decreased by 0.35 m,and the soil water content decreased correspondingly. The dynamic simulation by FLAC3D showed that the minimum safe distances between transverse ditch 1,vertical ditch and levee toe should be 25 m and 13 m respectively. The digging depth of transverse ditch and vertical ditch should be 1.2 m and 1.0 m respectively. If the width of marshland in drought period was less than 500 m,one transverse ditch was efficient. Otherwise,more transverse ditches should be set with the intervals of 300 m. Conclusions The project of ditching for drain is an effective ecological snail elimination method. Optimizing the digging depth of ditches and distances between transverse ditches,vertical ditch and levee toe will en?sure the effects and security of the project.
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Objective To evaluate the effect of ditching for drain on the control of the breed of Oncomelania hupensis snails in beaches of Dongting Lake. Methods From November,2009 to November,2012,an O. hupensis snail infested beach of the Yueyang jail and an O. hupensis snail infested beach of Junshan District were selected as research fields in the eastern Dongting Lake area,and the former,as the intervention field,was performed with the ditching for drain by excavators and the latter,as the control field,was not. Results Before the project implemented,the average soil moisture contents on the beaches in dry seasons of the two fields were both about 35.56%. After the project implemented,in the intervention field,the average soil mois?ture content was 26.53%which was significantly lower than that(35.56%)in the control field(F=6.53,P0.05),and after the project implemented(in 2012),no adult and young snails were found in the interventional field,but in the control field,the average densities of living snails and young snails were 29.37 snails/0.1 m2 and 213±108.45 snails/0.1 m2 respectively. Conclusion The intervention of ditching for drain can decrease the soil moisture contents quickly and change the ecological condition,therefore,can control the breed of O. hupensis snails in the beaches of Dongting Lake.
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Objective To study the morphological change of Schistosoma japonicum eggs processed by calcium cyanamide synthetic drug,so as to provide the basis for further study of the mechanism that calcium cyanamide synthetic drug to schisto?some eggs. Methods The calcium cyanamide synthetic drug was added to the cattle feces containing schistosome eggs and mixed up,and then the cattle feces was stacked as original shape on the marshland. Blank controls were set at the same time. The cattle feces samples were collected and the schistosome eggs were observed under a microscope on the 1st,2nd,3rd,7th day after the experiment. Results By the effect of calcium cyanamide synthetic drug,the color of eggs was deepening gradual?ly,the miracidia were atrophied,and the shells of eggs were thickened. The embryonic membrane of miracidia was no longer completed 3 days later,and the miracidia were deformed severely 7 days later. The atrophy of miracidia was not obvious in the blank controls. Conclusion The schistosome miracidia and embryonic membrane can be damaged by the calcium cyanamide synthetic drug,and worse damaged with time extending.
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Objective To observe the effects of calcium cyanamide (Rongbao) on the histological and morphological changes of Oncomelania hupensis snails in order to explore its molluscicidal mechanisms.Methods The serial snails' slides were fixed after soaking in a concentration of Rongbao leached liquor at different time.The histological and morphological changes of the snails were compared among these slides.Results After soaking in the Rongbao leached liquor for 48 h,the mantle epithelia,respiratory epithelia of the gill,liver cells,and muscle cells of gastropods were injured seriously,which resulted in the death of the snails directly.The death rates of the snails were 96.70% and 100% after soaking in the Rongbao leached liquor for 48 h and 72 h,respectively.Conclusion Rongbao is an effective molluscicide by damaging the several snail tissues.
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0. 05), Conclusion There was the same molluscicidal effect while the active content of SCN was a guarter of active content of WPN by immersion and spraying in the field. SCN is a novel form of niclosamide with high molluscicidal effect and of convenience to use in the field.
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Objective To explore susceptibility of praziquantel(PQT) against Schistosoma japonicum in the repeated chemotherapy areas in Dongting Lake region of China. Methods Sixty mice were divided into two groups, and infected respectively by cercariae released from the infected snails which were collected from new and old endemic areas. After 5 weeks, the mice in each group were divided into control groups and treatment groups (PQT group). The mice in each PQT group were treated with a single oral dose of praziquantel (600 mg/kg). Three weeks post treatment, mice were dissected, and the number of adults, the stool eggs per gram (EPG), the liver EPG and the hatching rates were observed. Results The worm reduction rates of the PQT groups of new and old epidemic areas were 98.24% and 98.71% respectively, and the stool egg reduction rates 99.94% and 99.64%, the liver egg reduction rates 75.85% and 73.10%,and there were no significant differences between the new and old endemic areas. The stool hatching test was positive in the control groups, and negative in the PQT groups. Conclusion Susceptibility of praziquantel against Schistosoma japonicum does not decrease in repeated chemotherapy areas in Dongting Lake region.