[Spatial distribution characteristics of in different water systems in Anqing City from 2016 to 2022].

Objective: To investigate the distribution of snails in different water systems in Anqing City from 2016 to 2022, so as to provide insights into snail control in the city.

Methods: Snail survey data and distribution of water systems in snail-infested environments were collected from schistosomiasis-endemic areas of Anqing City from 2016 to 2022. The vector maps of towns and water systems in Anqing City were downloaded from National Geomatics Center of China. The GPS toolbox APP version 2.7.9 was downloaded from a smartphone to record the longitude and latitude of each snail-infested environment in Anqing City, which were loaded into the software LocaSpace Viewer version 4.4.6 to map the distribution of snail-infested environments. The area of snail habitats, area of emerging snail habitats, area of re-emerging snail habitats, type of snail habitats and density of living snails were descriptively analyzed. The spatial database of snail-infested environments in Anqing City was built with the software ArcGIS version 10.8, and the density of living snails was subjected to spatial autocorrelation analysis in snail-infested environments. The hotspot clusters of density of living snails were identified in snail-infested environments and the density of living snails was subjected to standard deviation ellipse analysis in snail-infested environments.

Results: A total of 515 snail-infested environments were identified in water systems in Anqing City in 2022. The area of snail habitats reduced from 6 909.32 hm in 2016 to 6 087.48 hm in 2022, with a reduction of 11.89%, and the areas of snail habitats reduced by 2.39%, 21.71% and 1.67% in the main stream of the Yangtze River, the Wanhe River system and the Caizihu River system in Anhui City, respectively, while the area of snail habitats increased by 3.94% in the Huayang River system. Emerging or re-emerging snail habitats were identified in Anqing City each year during the period from 2016 to 2018 and from 2020 to 2020. The density of living snails appeared a tendency towards a decline in the Wanhe River system ( = -0.030, = -3.019, < 0.05) and Huayang River system ( = -0.029, = -4.296, < 0.05) in Anqing City from 2016 to 2022, and fluctuated in the main stream of the Yangtze River ( = 0.028, = 1.019, > 0.05) and the Caizihu River system ( = 0.020, = 1.877, > 0.05). A positive global spatial autocorrelation was identified in the density of living snails in Anqing City each year from 2016 to 2022 (all Moran's values > 0, all values < 0.05), and the hotspot clusters of density of living snails in snail-infested environments were mainly distributed in the Wanhe River system (Shankou Township, Hongpu Township, Yueshan Township and Wanghe Townshpi), the main stream system of the Yangtze River (Dalongshan Township, Wanhe Farm, Haikou Township and Huayang Township), the Huayang River system (Dashi Township and Xuqiao Township) and the Caizihu River system (Xiushan Township and Fangang Township). The ratio of the long to short axes of the standard deviation ellipse was 1.72 to 2.06 for the density of living snails in snail-infested environments in Anqing City from 2016 to 2022, and snails were mainly distributed in the southwest to northeast, and appeared the east-west and north-south spread.

Conclusions: The areas of snail habitats and the density of living snails appeared a tendency towards a decline in different water systems in Anqing City from 2016 to 2022; however, there is still a risk of snail spread. Reinforced surveillance and precision control of snails are required in Anqing City.