Abstract: Objective　To investigate the distribution characteristics of Oncomelania hupensis snails in Yunnan Province following interruption of schistosomiasis transmission, so as to provide the evidence for assessing the risk of schistosomiasis transmission and scientifically formulating the schistosomiasis surveillance program. Methods　According to the requirements of the National Schistosomiasis Surveillance Scheme (2020 Edition), O. hupensis snail surveillance data were collected from 18 schistosomiasis⁃endemic counties (cities, districts) in Yunnan Province from 2020 to 2024, including area of snail survey, area of snail habitats, area of re⁃emerging snail habitats, number of frames surveyed, number of frames with O. hupensis snails, number of O. hupensis snails captured, and number of living snails, and the occurrence of frames with snails and mean density of living snails were calculated. Changes in snail status over the 5⁃year period from 2020 to 2024 and the differences in snail distributions specified by epidemic intensity, environmental type, and vegetation type were analyzed. Results　The areas of snail survey increased from 1 727.96 hm2 in 2020 to 3 894.45 hm2 in 2024 (peak) across 18 schistosomiasis⁃endemic counties (cities, districts) in Yunnan Province during the period from 2020 through 2024. The areas of snail habitats increased from 70.36 hm2 in 2020 to a peak in 2023 (172.04 hm2), followed by a reduction to 132.36 hm2 in 2024, and the areas of re⁃emerging snail habitats increased from 42.71 hm2 in 2020 to a peak in 2022 (78.43 hm2), followed by a reduction to 40.21 hm2 in 2024. The occurrence of frames with snails and mean density of living snails increased from 1.24% (3 025/244 404) and (0.033 2 ± 0.038 7) snails/0.1 m2 in 2020 to peaks at 2.03% (6 231/307 563) and (0.066 9 ± 0.068 4) snails/0.1 m2 in 2023, followed by reductions to 1.04% (5 829/559 941) and (0.032 6 ± 0.057 7) snails/0.1 m2 in 2024, respectively. There was a significant difference in the occurrence of frames with snails over the 5⁃year study period ([χ2] = 1 962.95, P < 0.05), and the occurrence of frames with snails reduced by 48.71% in 2024 relative to in 2023 ([χ2] = 1 411.05, P < 0.005); however, there was no significant difference in the mean density of living snails over the 5 years (H = 5.310, P > 0.05). There were significant differences in the occurrence of frames with snails ([χ2] = 481.27, P < 0.05) and mean density of living snails (H = 6.872, P < 0.05) in schistosomiasis⁃endemic areas with different epidemic intensities. The occurrence of frames with snails ([χ2] = 25.32 and 38.70, both P values < 0.017) and mean density of living snails (Z = 28.55 and 49.96, both P values < 0.017) were higher in schistosomiasis transmission⁃interrupted and eliminated areas with snails than in schistosomiasis⁃eliminated areas without snails, and the occurrence of frames with snails ([χ2] = 453.54, P < 0.017) and mean density of living snails (Z = -56.97, P < 0.017) were higher in schistosomiasis⁃eliminated areas with snails than in schistosomiasis transmission⁃interrupted areas with snails. O. hupensis snails were mainly distributed in paddy fields, dry farmlands and ditches; however, the occurrence of frames with snails (13.40%, 424/3 164) and mean density of living snails [(0.252 8 ± 0.158 7) snails/0.1 m2] were higher in ponds/weirs than in other types of environments (both P values < 0.05). Rice, dry farmland crops and weeds were main vegetations in which O. hupensis snails were distributed, and the occurrence of frames with snails (2.29%, 7 111/310 140) and mean density of living snails [(0.072 3 ± 0.018 9) snails/0.1 m2] were higher in weeds than in other types of environments (both P values < 0.05). Conclusions　O. hupensis snails have been effectively controlled in Yunnan Province following implementation of integrated schistosomiasis control measures; however, there are still risk factors for schistosomiasis transmission, including reduced attention to schistosomiasis control and snail re⁃emergence. Improved control efforts and surveillance system construction and timely identification of risk factors of snail status and timely management are recommended to ensure the achievement of the target of schistosomiasis elimination as scheduled. 

Key words: Schistosomiasis, Oncomelania hupensis, Surveillance, Yunnan Province, Post?transmission interruption

摘要： 目的　了解云南省血吸虫病传播阻断后钉螺分布特征，为评估血吸虫病传播风险、科学制定监测方案提供参考。方法　按照《全国血吸虫病监测方案（2020年版）》要求，收集2020—2024年云南省18个血吸虫病流行县（市、区）钉螺监测数据，包括钉螺调查面积、查出有螺面积、复现有螺面积、调查框数、有螺框数、捕获螺数、活螺数等指标，计算有螺框出现率和活螺平均密度，分析5年间螺情变化及不同流行程度地区、不同环境类型、不同植被类型间螺情分布差异。结果　2020—2024年云南省18个血吸虫病流行县（市、区）钉螺调查面积从2020年的1 727.96 hm2增至2024年的3 894.45 hm2（峰值）；查出有螺面积从2020年的70.36 hm2增至2023年的172.04 hm2（峰值），2024年降至132.36 hm2；复现有螺面积从2020年的42.71 hm2增至2022年的78.43 hm2（峰值），后降至2024年的40.21 hm2；有螺框出现率和活螺平均密度分别从2020年的1.24%（3 025/244 404）、（0.033 2 ± 0.038 7）只/0.1 m2升至2023年的2.03%（6 231/307 563）、（0.066 9 ± 0.068 4）只/0.1 m2（均为峰值），2024年分别降至1.04%（5 829/559 941）、（0.032 6 ± 0.057 7）只/0.1 m2，各年有螺框出现率差异有统计学意义（[χ2] = 1 962.95，P < 0.05）；2024年有螺框出现率较2023年下降了48.71%，差异有统计学意义（[χ2] = 1 411.05，P < 0.005）；但2020—2024年各年活螺平均密度差异无统计学意义（H = 5.310，P > 0.05）。不同血吸虫病流行程度地区有螺框出现率（[χ2] = 481.27，P < 0.05）和活螺平均密度（H = 6.872，P < 0.05）差异均具有统计学意义，达到传播阻断标准的有螺区和达到消除标准的有螺区有螺框出现率（[χ2] = 25.32、38.70，P均< 0.017）和活螺平均密度（Z = 28.55、49.96，P均< 0.017）均高于达到消除标准的无螺区；达到消除标准的有螺区有螺框出现率（[χ2] = 453.54，P < 0.017）和活螺平均密度（Z = −56.97，P < 0.017）均高于达到传播阻断标准的有螺区。钉螺主要分布于水田、旱地和沟渠，但塘堰有螺框出现率［13.40%（424/3 164）］和活螺平均密度［（0.252 8 ± 0.158 7）只/0.1m2］均高于其他环境类型（P均< 0.05）；钉螺分布环境的植被以水稻、旱地作物、杂草为主，杂草环境有螺框出现率［2.29%（7 111/310 140）］和活螺平均密度［（0.072 3 ± 0.018 9）只/0.1 m2］均高于其他植被类型（P均< 0.05）。结论　云南省通过实施血防综合治理措施有效控制了螺情，但存在重视程度下降、钉螺复现等风险因素，今后应继续加强防治力度和监测体系建设，及时发现螺情风险因素并进行治理，以确保如期实现血吸虫病消除目标。

关键词: 血吸虫病, 钉螺, 监测, 云南省, 传播阻断后