Potential Impact of Flood on Schistosomiasis in Poyang Lake Regions Based on Multi-Source Remote Sensing Images Jing-Bo Xue NIPD: National Institute of Parasitic Diseases Xin-Yi Wang National Institute of Parasitic Disesses Li-Juan Zhang NIPD: National Institute of Parasitic Diseases Yu-Wan Hao NIPD: National Institute of Parasitic Diseases Zhe Chen Jiangxi Institute of Parasitic Diseases Dan-Dan Lin Jiangxi Institute of Parasitic Diseases Jing Xu National Institute of Parasitic Diseases Shang Xia ( [email protected] ) NIPD: National Institute of Parasitic Diseases Shi-Zhu Li NIPD: National Institute of Parasitic Diseases Research Keywords: Schistosomiasis, Flood disaster, Remote sensing, Water extraction Posted Date: October 20th, 2020 DOI: https://doi.org/10.21203/rs.3.rs-92265/v1 License: This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License Version of Record: A version of this preprint was published on February 22nd, 2021. See the published version at https://doi.org/10.1186/s13071-021-04576- x. Page 1/13 Abstract Background Flooding may be the most important factors contributing to the rebound of Oncomelania hupensis in endemic foci. This study aimed to assess the risk of schistosomiasis japonica transmission impacted by ooding around the Poyang Lake region using multi-source remote sensing images. Methods Normalized Difference Vegetation Index (NDVI) data collected by the Landsat 8 satellite was used as an ecological and geographical suitability indicator of O. hupensis snail habitats in the Poyang Lake region. The ood-affected water body expansion was estimated using dual polarized threshold calculations based on the dual polarized synthetic aperture radar (SAR). The image data were captured from Sentinel-1B satellite in May 2020 before the ood and in July 2020 during the ood. The spatial database of snail habitats distribution was created by using the 2016 snail survey in Jiangxi Province. The potential spread of O. hupensis snails after the ood was predicted by an overlay analysis of the NDVI maps of ood-affected water body areas. In addition, the risk of schistosomiasis transmission was classied based on O. hupensis snail density data and the related NDVI. Results The surface area of Poyang Lake was approximately 2,207 km2 in May 2020 before the ood and 4,403 km2 in July 2020 during the period of the ood peak, and the ood-caused expansion of water body was estimated as 99.5%. After the ood, the potential snail habitats were predicted to be concentrated in areas neighboring the existing habitats in marshlands of the Poyang Lake. The areas with high risk of schistosomiasis transmission were predicted to be mainly distributed in Yongxiu, Xinjian, Yugan and Poyang (District) along Poyang Lake. By comparing the predictive results and actual snail distribution, the predictive accuracy of the model was estimated as 87%, which meant the 87% of actual snail distribution were correctly identied as the snail habitats in the model predictions. Conclusions Flood-affected water body expansion and environmental factors pertaining to snail breeding may be rapidly extracted from Landsat 8 and Sentinel-1B remote sensing images. The applications of multi-source remote sensing data are feasible for the timely and effective assessment of the potential schistosomiasis transmission risk caused by snail spread during the ood disaster, which is of great signicance for precision control of schistosomiasis. Background Schistosomiasis japonica, caused by infection with Schistosoma japonicum, is a zoonotic parasitic disease [1]. In China, schistosomiasis is mainly concentrated along the south of the Yangtze River basin, and has a substantial impact on human health and socioeconomic development [2, 3]. Oncomelania hupensis is a freshwater snail species and the only intermediate host of S. japonicum. [4]. O. hupensis is mainly distributed along the river system and plays a critical role in the transmission of schistosomiasis. Studies have shown that the geographical distribution of schistosomiasis is strongly associated with the distribution of O. hupensis[3]. O. hupensis is predominantly distributed in marshland and lake areas along the middle and lower reaches of the Yangtze River in the provinces of Hunan, Hubei, Jiangxi, Anhui and Jiangsu. This area covers a landmass of 3.484 to 3.611 billion m2 and accounts for a geographic distribution of 97.32% to 98.9% of snail habitats in China [5]. Since China moved towards elimination of schistosomiasis in 2016, disease endemicity has been maintained at a historically low level in the country, with the exception of regions with extensive snail habitats [6]. Regular seasonal uctuation of the water body level create favorable conditions for snail breeding in marshlands around Poyang Lake. Flooding in the area in 2017 has contributed to the expansion of snail habitats along Poyang Lake [7-9] by 490 billion m2, accounting for 98% of newly-detected and re-emerging snail habitats in Jiangxi Province [10]. Additionally, infected bovines maintain a reservoir of schistosomiasis infection in the Poyang Lake region, acting as a source of onward transmission [11]. Recently, regions at schistosomiasis transmission have been identied by wild feces surveillance [12, 13], detection of infected snails by loop-mediated isothermal amplication (LAMP) [14, 15] and sentinel mice- base surveillance [16, 17]. Since June 2020, continuous heavy rainfall along the middle and lower reaches of the Yangtze River has resulted in severe ood disasters along the Yangtze River basin and around the Poyang Lake area in China. The highest recorded water level exceeded that of previous record highs following ooding in 1998, and has led to dyke collapse and water logging in many urban areas in China. Control of schistosomiasis in ood-affected areas has been impacted by increased contact with infested water during the ght against oods, and increased spreading of snails attributed to ooding. The aim of this study was to predict the expansion of O. hupensis snail habitats impacted by ooding and to assess the associated potential risk of schistosomiasis transmission in the Poyang Lake area using multi-source remote sensing image data and Sentinel-1B satellite radar images. Methods Study area Poyang Lake, the largest freshwater lake in China, is located in the middle and lower reaches of the Yangtze River in the north of Jiangxi Province (N 28˚22' to 29˚45', E 115˚47' to 116˚45'). The ecological and geographical features of the Poyang Lake are suitable for snail breeding. The lake is fed by water from inland rivers between April and June, and by the Yangtze River between July and September, maintaining a high water level during the spring and summer seasons.. Page 2/13 A total of 13 counties (cities, districts) are endemic for schistosomiasis endemic around the Poyang Lake area, including Nanchang, Xinjian, Jinxian, the high- tech zone of Nanchang City, Yongxiu, Gongqingcheng, Lushan, Lianxi, Hukou, Duchang, Poyang, Yugan and Wannian (Figure 1). Snail distribution Data on snail distribution was obtained from a snail survey carried out in Jiangxi Province in 2016 [10]. The geographical and environmental characteristics of snail distribution were extracted for the 13 counties (cites, districts) in which schistosomiasis is endemic, and the spatial database of snail distribution in Poyang Lake areas was created accordingly. A 75% subset of the snail distribution data was randomly selected as a model training dataset, and the remaining 25% were assigned as the model validation dataset. Multi-source remote sensing images Remote sensing image data collected by the Landsat 8 satellite, with a spatial resolution of 30 m following geometric correction, convolution interpolation and resampling, were extracted from the NASA EarthData database (https://earthdata.nasa.gov/). Operational Land Imager (OLI) multi-wave remote sensing images were obtained for May 2016, the time period during which the snail survey was conducted. Sentinel-1B synthetic aperture radar (SAR) images were obtained from the European Space Agency (ESA) Earth Online database (https://earth.esa.int/), and remote sensing image data were obtained from the Sentinel-1B dual-polarized (HV + HH) SAR data for May 15, 2020 corresponding to the time period before the ood and for July 14, 2020, corresponding to the peak ood time period. An interferometric wide swath mode was assigned as the image mode. Remote sensing image data inversion NDVI data were used as a measure of vegetation coverage in snail habitats, calculated using the following formula: where NIR indicates the reectance in near-infrared wavelengths, and R indicates the reectance in visible red wavelengths. Maximum and minimum NDVI values for snail habitats around the Poyang Lake area were calculated based on a dataset of 75% of snail distribution sites. Flood-cased expansion of water body areas were identied using dual polarized threshold calculations for the ooding time period [18]. SAR images were segmented by estimation of small backscattering coecient thresholds of water on SAR images. Segmentation results were saved as classication result les and classication results were post-processed. Incorrect extraction images were removed through a human-computer interaction system to yield the nal water body data. Sentinel-1B satellite data were processed using the SAR Scape module in ENVI software version 5.3, which mainly included radiometric calibration, ltering processing, terrain