Abstract: Objective To understand the status of snail distribution after flooding in Anhui Province in 2020 for evidence to formulate corresponding prevention and control measures. Methods The data on the rainfall and water level in flood season in 2020 as well as disaster information of schistosomiasis in the endemic areas in Anhui were collected and analyzed. In 2021, the snail habitats were investigated in 50 counties of 9 cities where schistosomiasis was endemic, and the information of snail breeding environment, snail distribution, newly emerging and re-emerging snails were collected to analyze the diffusion of snails in Anhui after the flood. Results In flood season of 2020, the middle and lower reaches of the Yangtze River were hit by heavy rainfall, with rainfall of 317.9 mm in July. The average water level recorded at Datong hydrological station was 15.29 m in July, and the monthly maximum water level in July and August reached 16.2 m and 15.4 m respectively, both exceeding the water line for alarming (14.4 m) at the station. A total of 71.43% of the endemic towns and 47.98% of the endemic villages in across Anhui were affected by the flood disaster, resulting in embankment breaches at 130 places. In 2021, snails were found in an area of 20 238.26 hm², of which 16 781.86 hm² of lake and river beach were the major snail habitats. The area of snail re-emerging was 976.84 hm2 in total, in which 685.10 hm² was recurrent area of Oncomelania hupensis caused by the flood. The area of newly emerging snail was 611.52 hm², of which 482.23 hm² was associated with the flood. The areas with re-emerging or newly emerged snails were primarily in the Yangtze River and its tributaries, among which the area of snail re-emerging in the main stream of the Yangtze River was 275.65 hm²(28.22%), and the area of snail newly emerging was 223.93 hm²(36.62%). The environment with snail re-emerging or newly emerging was most seen in beaches, where snails were re-emerged in 515.54 hm²(52.78%), and newly emerged in 470.79 hm²(76.99%). In the areas with different epidemic degrees, snail re-emerging or newly emerging was found in transmission interruption areas, where Oncomelania hupensis was re-emerged in 917.45 hm²(93.92%), and newly emerged in 526.53 hm²(86.10%). Among the different epidemic types, the area of re-emerging and newly emerging snail habitats was more in the marshland and lake regions, accounting for 567.87 hm² (58.13%) and 477.79 hm²(78.13%), respectively. Conclusion The flooding in 2020 produced serious impact on snail diffusion in Anhui Province. Therefore, it is necessary to enhance snail surveillance, risk assessment of schistosomiasis and control of the snails in key environment.

Key words: Schistosomiasis, Flooding, Diffusion of snails, Anhui Province