| Schistosomiasis japonicum is a major zoonose threatening human health,the epidemic situation of S.japonicum has rebound in china recently.Oncomelania hupensis is the only intermediate host of S.japonicum,which is the key point in transmission of the S.japonicum.The ecological changes such as construction of Three Gorges Reservoir and global warming may induce O.hupensis Large-scale spread and engender new epidemic areas.Research on O.hupensis ecology especially O.hupensis population dynamics can supply information for controlling the O.hupensis;In our study,we made a dynamic observation on the O.hupensis population In the new era,which included O.hupensis distribution,risk factors of the distribution,population density and structure etc.Part 1 Dynamic studies on the distribution of the Oncomelania hupensisObjective To study the distribution of the Oncomelania hupensis and supply the theoretical information for snail ecology and population dynamics.Methods A bottomland close to Junshan Park in Yueyang City,Hunan Province and an environment called "lanbao" closed to Puge County,Sichuan Province were selected as the study field.The study period was from October,2007 to May,2008 for Hunan and Sichuan was from Feb,2008 to Feb,2009.Systematic sampling and Random sampling was separately designed to determine the sites of investigation where all the snails were collected and the number of live snails was counted by the method of dissection in the laboratory.Statistical indices of snails such as median,quartile range and aggregation index were first calculated to conduct a preliminary analysis.Then, negative binomial distribution,log-normal distribution,exponential distribution etc were fitted to the snail data to explore the snail distribution in different time.Results The snail distribution in the whole study period was basically positively skewed distribution.The median of the snail were 7,9,1,0,3,4 and 1per 0.01m~2 for Hunan and Sichuan 6.5,4.5,3,4.0,4.0,4.0,4.0,2.0,11.0,3.0,1.0,1.0和2.0 per 0.01m~2 respectively;The variance was larger than the mean in most months,and the aggregation index changed with the snail density with different direction according to Hunan and Sichuan.No distribution was successfully fitted to the Hunan snail data from the October,the snail data in the November was approximately log-normal distribution;both the exponential distribution and negative binomial distribution were fitted well to the Hunan snail data from April,2008,while the snail data from other months were all approximately negative binomial distribution.No distribution was successfully fitted to Sichuan snail at Jun,2008,Oct,2008,Dec,2008 and Feb,2009, the others were approximately negative binomial distribution.Conclusions The snail distribution was not the unique negative binomial distribution,but maybe dynamic distribution related with snail density.A new generalized distribution model was needed to reflect the dynamics of the distribution.Part 2 study on Micro-environment impact factors on Oncomelania hupensisObjectives To explore the relationship of the snail distribution and micro-environment factors so as to supply information for eliminating Oncomelania hupensis with ecology methods and controlling the Schistosomiasis..Methods Filed selection and sampling method was the same as the first part,the soil surface temperature and vegetation cover was measured partly when snail investigated,and about 30g soil samples were collected,the number of live snails was counted by the method of dissection at the laboratory,soil pH value and soil moisture was measured too. Statistical indices of snails such as median,variance,minimum value,maxium value etc were first calculated to conduct a preliminary analysis,then scatter diagram and spearman analysis between the factor and snail was done,finally general additive model for all facors and the curve model for each factor were fitted.Results 104 frames were surveyed at Hunan field,while Sichuan was 75;ph value in Hunan was 4.7-7.92,where Sichuan was 4.88-7.77,the coverage of the grass in Hunan was 1 percent to 96 percent,where Sichuan was 1 percent to 100 percent;soil temperature in Hunan was 14.5℃-32.7℃,but 19.3℃-27.1℃in Sichuan;the water content of soil in Hunan was 0.07-2.00,where Sichuan was 0.14-0.85;the trend of the scatter diagram was different between the two sites,most of the spearman analysis were not significant in statistics,curve models were fitted effectively,adjusted r~2 was around 0.9;General additive model for all factor was fitted,which showed the coverage was not significant in hunan field,while other factors were all significant;After the deduction of linear and other factors the curv relationship between micro-environmental factors and snail was different with that single-factor fitted;the relative effective to the snail distribution was different between the two field.Conclusion the relationship was different between snail and factors in Hunan and Sichuan;smoothess function relationship was shown with the snail and factors,negative binominal regression or other linear regress model were not suggested fitted simply;different methods should be adopted in Sichuan an Hunan to change the ecology of the snail so as to control the diffusion and propagation of the snail.Part 3 Observation on Oncomelania hupensis populationObjectives To explore the dynamic change of the snail density and age composition under nature environment at different months so as to supply information for controlling the spread of the snail and prevent the epidemic of Schistosomiasis.Methods Filed selection and sampling method was the same as the first part,firstly the body,sex,survival status were measured,then the number of live snails was counted with each frame,german of the O.hupensis was dissected and observed by electron microscope followed.Draw the line graph of density and mortality,bar graph of body indices and sex;snails that length more than 5mm or less was distinguished as mature of immature for the Sichuan snail and snails that snail big than 5 or less was distinguished as mature or immature for Hunan snail,and the bar graph of the age composition was plotted.The germen distribution of O.hupensis was describedResults density of Hunan snail had a decreasing trend,mortality keep at a high level and immature O.hupensis existed all the year basically,whose proportion however kept in a low level,renewal was not happened.The proportion of female and mail had no significant difference,Germen of the female O.hupensis shrank at May 2008, which shrank overly at August 2008 under water,the mail O.hupensis showed no significant change;though electron microscopy it was found that snail gonad had significant changes under snow frozen weather and water.Density of Sichuan snail fluctuated and was highest at October 2008,when renewal of the snail happened,mortality was at a low level,The proportion of female and mail snail showed no significant difference.The germen of female O.hupensis was plumpy at May 2008,which got plump overly at August 2008,it begun to shrink at Sep,and got quite atrophic at Nov 2008,there no significant changes at snail gonad was found by electron microscopy.Conclusion The endure long period of snow weather with low temperature affected the snail ecology at some degree maybe in Hunan,density of the snail showed a decreasing trend and renewal was not formed,where renewal stage was happened at October 2008 for Sichuan,the population was at a dynamic equilibrium,it was found that snow frozen weather and water have a significant effect on snail'gonad by micro-electron microscopy;we should adopt different methods to control snail proliferation so as to prevent epidemic of Schistosomiasis based on the different ecology structure. |
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