Surveillance on potential factors influencing schistosomiasis prevalence in water system of Bianmin River Ⅰ Distribution and dynamics of Oncomelania snails / 中国血吸虫病防治杂志

ABSTRACT

Objective To understand the distribution,variance and dynamics of Oncomelania snails in the water system of the Bianmin River after the river bank being protected with concrete.Methods The snails in the water system of the Bianmin River were investigated with the systemic sampling method and environmental spot-checking method in spring from 2002 to 2005.The indexes including area with snails,area with infected snails,rate of frames with snails,density of living snails and infection rate of snails in different environments were collected,analyzed and compared year by year.Results From 2002 to 2005,in the main river of the water system of the Bianmin River,irrigation areas and the adjacent marshlands of the Yangtze River,the areas with snails were 20.94-31.88,39.30-48.08 hm2 and 275.13-292.31 hm2,respectively;the rates of frames with snails were 9.96%-21.88%,29.61%-58.54% and 62.14%-85.97%,respectively;the mean densities of snails were 0.97-1.86,0.92-3.96 snails/0.1 m2 and 7.72-11.15 snails/0.1 m2.In 2005,in the main river,irrigation areas and the adjacent marshlands,the rates of frames with snails were 21.88%,39.33% and 83.81%,respectively;the densities of living snails were 1.30,3.96 snails/0.1 m2 and 11.15 snails/0.1 m2.During the last four years,the rates of frames with snails increased quickly in the main river of the water system of the Bianmin River;the densities of snails increased by 4 times in the irrigation areas;the indexes mentioned above were stable in the adjacent marshlands of the Yangtze River.However,the rate of frames with snails in the marshlands was 2-3 times higher than that in the irrigation areas and the mean density of snails in the marshlands was 3-8 times higher than that in the irrigation areas.Conclusions The main factor causing the increase of snails is that the river beach has not been cleaned yet in the water system of the Bianmin River,and so the key of schistosomiasis control is that first,the river beach should be cleaned completely,and at the same time,strengthening the snail control in the irrigation areas and the snail surveillance and snail control with molluscicides in the outfalls of the rivers of the water system of the Bianmin River to the Yangtze River.