National Institute of Parasitic Diseases, China CDC (Chinese Center for Tropical Diseases Research) Key Laboratory On Parasite and Vector Biology, National Health Commission WHO Collaborating Centre for Tropical Diseases, National Center for International Research On Tropical Diseases, Ministry of Science and Technology, Shanghai, 200025, China.
Fudan University School of Life Sciences, Shanghai, 200438, China.
Parasit Vectors. 2024 Jul 7;17(1):291. doi: 10.1186/s13071-024-06318-1.
Oncomelania hupensis is the exclusive intermediate host of Schistosoma japonicum in China. Snail control is an essential component of schistosomiasis elimination programme. With 70 years of continuous efforts, the range of O. hupensis had reduced significantly, but slowed down in last decades. A large number of levees against flooding were constructed along Yangtze River and its affiliated lakes in the middle and lower reaches, which influenced the hydrology and ecology in the alluvial plains. The purpose of this study was to assess the impact of levees on the distribution of O. hupensis in the middle and lower reaches of the Yangtze River.
The snail habitats were digitalised by hand-held GPS system. The years for discovery and elimination of snail habitats were extracted from historical records. The accumulated snail-infested range for each habitat was calculated on the basis of annual reports. The current distribution of O. hupensis was determined by systematic and environmental sampling. The geographical distribution of levees was obtained from satellite imagery. To assess the impact of levees, the data pertaining to O. hupensis were divided into two parts: inside and outside the Yangtze River. Joinpoint regression was utilised to divide the study time span and further characterise the regression in each period. The 5-year-period moving averages of eliminated area infested by snails were calculated for the habitats inside and outside Yangtze River. The moving routes of corresponding geographical median centres were simulated in ArcGIS. Hotspot analysis was used to determine the areas with statistical significance clustering of O. hupensis density.
Three periods were identified according to Joinpoint regression both inside and outside Yangtze River. The area infested by O. hupensis increased in the first two periods. It decreased rapidly outside Yangtze River year over year after 1970, while that inside the Yangtze River did not change significantly. Furthermore, the latter was significantly higher than the former. It was observed that the present density of O. hupensis inside Yangtze River was lower than outside the Yangtze River. The median centre for eliminated ranges inside Yangtze River wavered between the east (lower reach) and the west (middle reach). In contrast, the median centre for eliminated ranges continuously moved from the east to the west.
Our findings indicated that the levees had a considerable negative impact on the distribution of O. hupensis outside Yangtze River. Some hotspots observed in the irrigation areas need a sluice system at the inlet of branch for snail control. The major distribution of O. hupensis located in Hubei might be caused by severe waterlogging. The intensive surveillance should be implemented there. The biggest two freshwater lakes, the major endemic regions historically, were identified as cold spots. The long-term impact of Three Gorges Dam on the distribution of O. hupensis in the lakes should be monitored and evaluated.
钉螺是中国日本血吸虫的唯一中间宿主。钉螺控制是消除血吸虫病规划的重要组成部分。经过 70 年的持续努力，钉螺的分布范围已显著缩小，但在过去几十年中速度有所放缓。在长江中下游地区，修建了大量防洪堤坝，这影响了冲积平原的水文学和生态学。本研究旨在评估堤坝对长江中下游钉螺分布的影响。
使用手持 GPS 系统对螺区进行数字化。从历史记录中提取发现和消除螺区的年份。根据年度报告计算每个螺区的累计有螺面积。通过系统和环境抽样确定钉螺的当前分布。从卫星图像中获取堤坝的地理分布。为了评估堤坝的影响，将与钉螺有关的数据分为长江内外两部分。采用 Joinpoint 回归将研究时间段分为两部分，并进一步描述每个时期的回归特征。计算长江内外螺区消除面积的 5 年移动平均值。在 ArcGIS 中模拟相应地理中位数中心的移动路线。使用热点分析确定钉螺密度有统计学意义聚类的区域。
根据长江内外的 Joinpoint 回归，确定了三个时期。在头两个时期，钉螺感染面积增加。1970 年后，长江外的感染面积逐年迅速减少，而长江内的感染面积没有明显变化。此外，后者明显高于前者。观察到长江内的钉螺当前密度低于长江外。长江内消除范围中位数中心在东部（下游）和西部（中游）之间波动。相比之下，消除范围中位数中心连续从东向西移动。
我们的研究结果表明，堤坝对长江外钉螺的分布有相当大的负面影响。灌溉区的一些热点观察到需要在支流入水口设置水闸系统来控制钉螺。历史上主要分布在湖北的钉螺可能是由严重的渍水引起的。应在那里进行密集监测。两个最大的淡水湖，历史上的主要流行地区，被确定为冷点。应监测和评估三峡大坝对湖泊内钉螺分布的长期影响。
