Abstract: Objective To understand the distribution trend of Oncomelania snails in Susong County for evidences to develop schistosomiasis control measures. Methods Snail data, including areas with snail prevalence, snail density and occurrence rate of live snails at individual frame, were collected from 2010 to 2021 in Susong County, and retrospectively analyzed for snail distribution across the county and in different endemic areas as well as the distribution trend of snails and the factors affecting the snail prevalence. Results The total area of Oncomelania hupensis in the county was maintained between 1 672.60 hm2 and 2 171.57 hm2, and appeared relatively stable from 2010 to 2021, during which the snail prevalence was 985.74-1 235.64 hm2 in marshland areas, with light fluctuation. The area with snail was 181.44-284.78 hm2 in lake regions, and tended to decrease, yet was 399.77-750.02 hm2 in inland regions, and tended to increase. The live snail density was 0.16-0.75 snails/0.11 m2 throughout the county, and the occurrence rate of live snails was 5.11%-11.78% at per frame. Live snail density remained relatively stable in the marshland and lake regions, whereas tended to increase from the lower level in inland areas. Live snail occurrence at individual frame was fluctuated considerably in diverse endemic areas. No infected snails have been found since 2013. Conclusion Snail prevalence remains relatively stable in Susong County, yet tends to spread in inland areas, which suggests that snail monitoring and control shall be focused in the inland regions in order to consolidate the prevention and control efforts achieved in previous years. 

Key words: Schistosomiasis, Oncomelania snail, Susong County