Xue et al. Parasites Vectors (2021) 14:116 https://doi.org/10.1186/s13071-021-04576-x Parasites & Vectors RESEARCH Open Access Potential impact of fooding on schistosomiasis in Poyang Lake regions based on multi-source remote sensing images Jing‑Bo Xue1,2,3,4,5, Xin‑Yi Wang1,2,3,4,5, Li‑Juan Zhang1,2,3,4,5, Yu‑Wan Hao1,2,3,4,5, Zhe Chen6,7, Dan‑Dan Lin6,7, Jing Xu1,2,3,4,5, Shang Xia1,2,3,4,5*† and Shi‑Zhu Li1,2,3,4,5*† Abstract Background: Flooding is considered to be one of the most important factors contributing to the rebound of Oncomelania hupensis, a small tropical freshwater snail and the only intermediate host of Schistosoma japonicum, in endemic foci. The aim of this study was to assess the risk of intestinal schistosomiasis transmission impacted by food‑ ing in the region around Poyang Lake using multi‑source remote sensing images. Methods: Normalized Diference Vegetation Index (NDVI) data collected by the Landsat 8 satellite were used as an ecological and geographical suitability indicator of O. hupensis habitats in the Poyang Lake region. The expansion of the water body due to fooding was estimated using dual‑polarized threshold calculations based on dual‑polarized synthetic aperture radar (SAR). The image data were captured from the Sentinel‑1B satellite in May 2020 before the food and in July 2020 during the food. A spatial database of the distribution of snail habitats was created using the 2016 snail survey in Jiangxi Province. The potential spread of O. hupensis snails after the food was predicted by an overlay analysis of the NDVI maps in the food‑afected areas around Poyang Lake. The risk of schistosomiasis transmis‑ sion was classifed based on O. hupensis snail density data and the related NDVI. Results: The surface area of Poyang Lake was approximately 2207 km2 in May 2020 before the food and 4403 km2 in July 2020 during the period of peak fooding; this was estimated to be a 99.5% expansion of the water body due to fooding. After the food, potential snail habitats were predicted to be concentrated in areas neighboring existing habitats in the marshlands of Poyang Lake. The areas with high risk of schistosomiasis transmission were predicted to be mainly distributed in Yongxiu, Xinjian, Yugan and Poyang (District) along the shores of Poyang Lake. By compar‑ ing the predictive results and actual snail distribution, we estimated the predictive accuracy of the model to be 87%, which meant the 87% of actual snail distribution was correctly identifed as snail habitats in the model predictions. Conclusions: Data on water body expansion due to fooding and environmental factors pertaining to snail breeding may be rapidly extracted from Landsat 8 and Sentinel‑1B remote sensing images. Applying multi‑source remote sens‑ ing data for the timely and efective assessment of potential schistosomiasis transmission risk caused by snail spread during fooding is feasible and will be of great signifcance for more precision control of schistosomiasis. Keywords: Schistosomiasis, Flood disaster, Remote sensing, Water extraction *Correspondence: [email protected]; [email protected] †Shang Xia and Shi‑Zhu Li contributed equally to this work 1 National Institute of Parasitic Diseases, Chinese Center for Diseases Control and Prevention, Chinese Center for Tropical Diseases Research, Shanghai 200025, People’s Republic of China Full list of author information is available at the end of the article © The Author(s) 2021. 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The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/publi cdoma in/ zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Xue et al. Parasites Vectors (2021) 14:116 Page 2 of 13 Background highs following fooding in 1998, and has led to the col- Intestinal schistosomiasis, caused by infection with Schis- lapse of dikes and/or waterlogging in many urban areas in tosoma japonicum, is a zoonotic parasitic disease [1]. In China. Control of schistosomiasis in food-afected areas China, schistosomiasis is mainly concentrated along the has been impacted by increased contact with infested south of the Yangtze River basin, where it has a substan- water during the fght against foods and the increased tial impact on human health and socioeconomic devel- spreading of snails attributable to fooding. In this con- opment [2, 3]. Oncomelania hupensis, a small tropical text, the aim of this study was to predict the expansion freshwater snail, is an amphibious species, and water is of O. hupensis snail habitats impacted by fooding and one of the essential conditions for its growth and repro- to assess the associated potential risk of schistosomia- duction; these snails will not thrive in persistently dry sis transmission in the areas around Poyang Lake using areas. Young snails live in the water, and mature snails multi-source remote sensing image data and Sentinel-1B generally live on wet and food-rich land. Regions where satellite radar images. the water level varies signifcantly are suitable for snail breeding if the water fow is slow or the vegetation grows Methods well. Variations in water level greatly afect the reproduc- Study area tion and growth of snails [4, 5]. Poyang Lake, the largest freshwater lake in China, Oncomelania hupensis is the only intermediate host is located in the middle and lower reaches of the of S. japonicum. [6]. Studies have shown that the geo- Yangtze River in the north of Jiangxi Province graphical distribution of schistosomiasis is strongly (28°22′–29°45′N,115°47′–116°45′E). Te ecological and associated with the distribution of O. hupensis [3]. geographical features of Poyang Lake are suitable for Te primary distribution of O. hupensis along the river snail breeding. Te lake is fed by water from inland riv- system means that it plays a critical role in the trans- ers between April and June and by the Yangtze River mission of schistosomiasis. In China, O. hupensis is between July and September, which enables a high water predominantly distributed in marshland and lake areas level to be maintained during the spring and summer along the middle and lower reaches of the Yangtze seasons. A total of 13 counties (cities, districts) in the River in the provinces of Hunan, Hubei, Jiangxi, Anhui areas around Poyang Lake are endemic for schistoso- and Jiangsu. Tis area covers a landmass of 3.484 to miasis, including Nanchang, Xinjian, Jinxian, the high- 3.611 thousand km 2 and accounts for a geographic dis- tech zone of Nanchang City, Yongxiu, Gongqingcheng, tribution of 97.32–98.9% of snail habitats in China [7]. Lushan, Lianxi, Hukou, Duchang, Poyang, Yugan and China began programs to eliminate schistosomiasis in Wannian (Fig. 1). 2016, and since then disease endemicity has been main- tained at a historically low level in the country, with the Snail distribution exception of regions with extensive snail habitats [8]. Data on snail distribution were obtained from a snail Regular seasonal fuctuations in the water level of Poy- survey carried out in Jiangxi Province in 2016 [11]. Te ang Lake create favorable conditions for snail breed- geographical and environmental characteristics of snail ing in the marshlands around this lake. Flooding in the distribution were extracted for the 13 counties (cites, dis- area in 2017 contributed to the expansion of snail habi- tricts) in which schistosomiasis is endemic, and the spa- tats along Poyang Lake [5, 9, 10] by 490 thousand km2, tial database of snail distribution in the Poyang Lake area accounting for 98% of newly detected and re-emerging was created accordingly. In this study, a 75% subset of the snail habitats in Jiangxi Province [11]. Additionally, snail distribution data was randomly selected as a model infected bovines maintain a reservoir of schistoso- training dataset, and the remaining 25% of the data was miasis infection in the Poyang Lake region, acting as a assigned as the model validation dataset. source of onward transmission [12]. Recently, regions of schistosomiasis transmission have been identifed by Multi‑source remote sensing images wild feces surveillance [13], detection of infected snails Remote sensing image data collected by the Landsat 8 by loop-mediated isothermal amplifcation (LAMP) satellite, with a spatial resolution of 30 m following geo- [14, 15] and sentinel mice-base surveillance [16]. metric correction, convolution interpolation and resam- Since June 2020, continuous heavy rainfall along the pling, were extracted from the NASA EarthData database middle and lower reaches of the Yangtze River has (https ://earth data.nasa.gov/). Operational Land Imager resulted in severe food disasters along the Yangtze River (OLI) multi-wave remote sensing images were obtained basin and in the areas around Poyang Lake. Te highest for May 2016, the time period during which the snail sur- recorded water level exceeded that of previous record vey was conducted.