Population Dynamics Of Oncomelania Before And After Snail Control In Marshlands Of Changsha Section Of Xiang River

Schistosomiasis brings heaps of harmful effects to hosts.At once time it was more widespread in Changjiang drainage basin and Southern China.Oncomelania hupensis,the only intermediate host of Schistosoma japonicum,plays a vital role in the transmission and prevalence of Schistosomiasis.Changsha section of Xiang river includes two parts: Wangcheng section and the urban section.The urban section was considered to be an area without snails,while Zengpizhou in Wangcheng section has snail distribution..Wangcheng has reached the standard of interrupted the transmission of Schistosomiasis in 1992.Due to a variety of factors,snails have been found in many marshlands in Changsha section of Xiang river since snails were found in fujiazhou in 1997.To investigate the Oncomelania hupensis distribution and quantitative changes in each marshland of Changsha section,and to evaluate the effectiveness of snail control in recent years,we have made a consecutive investigation of snail distribution in marshlands from 2003 to 2008 according to the methods mentioned in "Handbook of Schistosomiasis Control".The main results obtained are as follows:Twenty-four marshlands were investigated continuously from 2003 to 2008.The total number of marshlands with snails were 20 which accounted for 83.3%of all marshlands investigated,and four marshlands had no snails.The number of marshland with snails respectively accounted for 66.67%,66.67%,70.80%,75.00%,62.50%and 62.50 %of the year investigated;Compared with 2008,in 2003 the number of marshlands with living snails,the rate of frame with snails,the average density of snails,the rate of living snails respectively decreased by 40.00 %,99.10%,99.74%,51.09%.Processed by SAS 9.1.3 Cochran-Armitage Trend Chi-Square Test,the rate of frames with snails (Z= 91.5602,P＜0.01) and the rate of living snails(Z=65.1332, P＜0.01) were different in each marshland,but the downward trend was significant.Among 20 marshlands with snails,5 marshlands have infected snails(all in Wangcheng section),occupying 25.00%of the whole.The general development tendency of infected snails is:the number of marshlands with infected snails has declined year by year,so have the average density of infected snails and the infection rate of snails.No marshlands with infected snails were found in Changsha section of Xiang River from 2007 to 2008.The research indicates that the combination of environment improvement and snail control by chemicals was much more effective than only the latter.The effect of snail control was more lasting and more thorough by utilizing higher or lower marshland and reclamation and plantation in all measures of environment improvement and construction on marshlands of Changsha section of the Xiang River.It may be related to water level and the climate that the number of marshland with snails, the total number of snails,the rate of frames with snails and the rate of living snails decreased sharply in 2007 and 2008.The Oncomelania hupensis in the Changsha section of Xiang River have been well controlled.