THE POPULATION DYNAMICS OF ONCOMELANIA HUPENSIS AFTER SNAILS CONTROL IN MARSHLANDS IN CHANGSHA SECTION OF XIANG RIVER

Schistosomiasis brings heaps of harmful effects to hosts. It was more widespread in Changjiang drainage basin and Southern China. Oncomelania hupensis, theonly intermediate host of Schistosoma japonicum, plays a vital role in the transm ission and prevalence of Schistosom iasis. The urban section of Xiang River was considered to be an are awithout snails. Due to a variety of factors, snails have been found in many marshlands in Changsha section of Xiang River since snailswere found in fujiazhou in 1997. To investigate the distribution and quantitative changes of Oncomelania snails in each marshland of Changsha section of Xiang River, 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 by using the systematic and environmental sampling according to the methodsmentioned in “Hand book of Schistosom iasis Control”. Twenty-fourmarsh-lands were investigated continuously from 2003 to 2008. The total number of marsh lands with snails were 20 which accounted for 83.3% of all marsh lands investigated, and fourmarsh lands had no snails. The number of marsh land with living snails accounted for 62.50, 66.67, 66.6, 70.83, 33.33 and 37.50% of the year investigated respectively. Compared with 2008, the number of marsh lands with living snails, the rate of frame with snails, the average density of snails and the rate of living snails decreased 40.00, 99.10, 99.74 and 51.09% respectively in 2003. Processed by SAS9.1.3 Cochran-Armitage Trend Chi-Square Test, the rate of frames with snails (Z=91.56, P<0.01) and the rate of living snails (Z=65.13, P<0.01) were different in each marshland, and the downward trend was significant. Among the 20 marshlands with snails, 5 marshlands have infected snails, occupying 25.00% of the whole. The number of marshlands with in fected snails has declined year by year, so have the average density of infected snails and the infection rate of snails. Nomarshlands with infected snails were found in Changsha section of Xiang River from 2007 to 2008. The research indicated that the combination of environment improvement and snail control by chem icals 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, reclamation and plantation in all measures of snail control through environment improvement on marshlands in Changsha section of the XiangRiver. It may be related to water leveland the climate that the number of marshland with snails, the totalnumber of snails, the rate of frames with snails and the rate of living snails decreased sharply in 2007 and 2008. The Oncomelania hupensis in Changsha section of Xiang River have been well controlled.