Increase and decrease of Oncomelania snail population in Yizheng City in 2002～2008 and the control strategy

Objective To survey the increase and decrease of Oncomelania snail population before and after implementation of he Medium Term Planning for Control of Schistosomiasis in Yicheng(2004-2008),and to anlaysis of control measures.Methods The data concerning area with snails,area with infected snails,rate of frames with snails,density of viable snails and infection rate of snails in different environments were collected,analyzed and compared year by year from 2002 to 2008.At the same time,areas with snails on river beach and in rivers connected with the Yangtze River,area with snails and coverage rate of snail control areas were compared.Results Just before 2005,area with snails was larger.Then snail control measures were strengthened,and also comprehensive management of river beach and rivers connected with the Yangtze River was implemented.Area with snails decreased year by year.Inland snails and infected snails were finally eliminated.It was not yet clear if there were linear relationship between areas with snails on river beach and in rivers connected with the Yangtze River(r=0.393,P0.05).There is obvious negative correlation between area with snails and coverage rate of snail control areas(r =-0.891,P0.05).Conclusions The comprehensive chemical control of snails on river beach and river channels are the most direct and effective measures