Abstract: Objective　To investigate the trends in the prevalence of schistosomiasis in surveillance sites of Sichuan Province from 2020 to 2024, so as to provide insights into facilitating the elimination of schistosomiasis in hilly endemic areas. Methods　  A total 63 schistosomiasis⁃endemic counties (cities, districts) were selected in Sichuan Province as national schistosomiasis surveillance sites from 2020 to 2024, and transmission⁃interrupted and eliminated counties (cities, districts) with and without Oncomelania hupensis snails were classified into classⅡand Ⅲ surveillance counties (cities, districts), respectively. Two to three administrative villages were randomly sampled from each surveillance county (city, district) each year from 2020 to 2024 to investigate the prevalence of schistosomiasis. Mobile populations were screened for Schistosoma japonicum infections using indirect hemagglutination test (IHA), and sero⁃positives were subjected to parasitological tests using egg hatching test with nylon gauze and modified Kato⁃Katz thick smear method, with at least 200 populations investigated in each surveillance county (city, district). At least 100 livestock were tested for S. japonicum infections using miracidial hatching test across classⅡsurveillance counties (cities, districts). O. hupensis snail survey was performed in 3 administrative villages from classⅡsurveillance counties (cities, districts) with high⁃abundance snails, and 3 administrative villages randomly sampled from class Ⅲ surveillance counties (cities, districts) with a history of high⁃abundance snails, a high risk of introduction of snails or many settings suitable for snail breeding. At least 20% of class Ⅱ surveillance counties (cities, districts) were selected, and two administrative villages with a history of high⁃abundance snails, a high risk of introduction of snails, or many settings suitable for snail breeding were randomly selected from each county (city, district), followed by sampling of at least five settings from each village for snails and wild feces survey to monitor schistosomiasis transmission risk. All snails captured were examined for their viability using microscopy and tested for S. japonicum nucleic acid using loop⁃mediated isothermal amplification (LAMP) assay. Wild feces were tested for S. japonicum miracidia using miracidial hatching test. The mean density of living snails was subjected to clustering analysis using the software ArcGIS 10.4.1, spatial distribution maps of mean density of living snails were generated, and local spatial autocorrelation analysis was performed with hotspot analysis. Results　A total of 73 241 mobile populations were serologically screened for antibodies against S. japonicum in Sichuan Province from 2020 to 2024, and there were 355 cases tested positive for the anti⁃S. japonicum antibody, with a cumulative sero⁃prevalence rate of 0.48% (355/73 241). The sero⁃prevalence rates of anti⁃S. japonicum antibody were 0.69% (97/14 009), 0.68% (101/14 845), 0.46% (67/14 607), 0.34% (51/14 923), and 0.26% (39/14 857) from 2020 to 2024, with a reduction of 62.32% in 2024 relative to in 2020, and there was a significant difference in the sero⁃prevalence of S. japonicum among years ([χ2] = 43.530, P < 0.001). Nevertheless, all sero⁃positives were tested negative for S. japonicum infections by parasitological assays. In 2023, the highest sero⁃prevalence of S. japonicum was detected among mobile populations in Ziyang City (1.09%), and in other four years, the highest sero⁃prevalence was seen in Liangshan Yi Autonomous Prefecture, ranging from 1.43% to 3.18%, with significant differences seen in the sero⁃prevalence among regions from 2020 to 2024 ([χ2] = 4.913 to 129.440, all P values < 0.05). The sero⁃prevalence of anti⁃S. japonicum antibody was higher among male mobile populations than among females in Sichuan Province in 2024 ([χ2] = 5.663, P < 0.05), and there was no gender⁃specific sero⁃prevalence in other four years ([χ2] = 0.028 to 1.207, all P values > 0.05). There were occupation⁃specific sero⁃prevalence rates of anti⁃S. japonicum antibody in four years ([χ2] = 11.711 to 45.920, all P values < 0.05), except in 2023 ([χ2] = 2.044, P > 0.05), with higher sero⁃prevalence among government staff, construction workers, fishermen and boatmen, and students (all P values < 0.05). There were age group⁃specific sero⁃prevalence rates of anti⁃S. japonicum antibody among mobile populations each year from 2020 to 2024 ([χ2] = 16.523 to 35.616, all P values < 0.05), with the highest sero⁃prevalence among mobile populations at ages of 46 to 55 years in 2023 and at ages of 6 to 15 years in 2020, 2021, 2022 and 2024 (all P values < 0.05). A total of 8 316 livestock were tested for S. japonicum infections in national schistosomiasis surveillance sites in Sichuan Province from 2020 to 2024, and no infections were identified in livestock. O. hupensis snail survey was conducted covering an area of 14 703.90 hm2 in national schistosomiasis surveillance sites in Sichuan Province from 2020 to 2024, with 1 815.92 hm2 areas detected with snails, accounting for 12.35%            (1 815.92/14 703.90) of total survey areas. A total of 502 854 snails were captured, and no S. japonicum infection was identified in snails. The mean occurrence rate of frames with snails was 6.91% (247 844/3 587 122), and there was a significant difference in the occurrence of frames with snails among years ([χ2] = 289 707.440, P < 0.001, Cramer's V = 0.284). The mean density of living snails appeared a spatial autocorrelation and a spatial cluster pattern in Sichuan Province from 2021 to 2023 (Moran's I = 0.078 to 0.128, Z = 2.378 to 3.642, all P values < 0.05) and showed a random distribution pattern in 2024 (Moran's I = 0.049, Z = 1.622, P > 0.05). There were high⁃high clusters in the mean density of living snails in Yucheng District, Lushan County and Yingjing County of Ya'an City, Hongya County and Renshou County of Meishan City, Shizhong District of Leshan City, and Dayi County and Chongzhou City of Chengdu City (Z = 1.982 to 3.223, all P values < 0.05). A total of 2 599.89 hm2 areas of settings were surveyed for O. hupensis snails during the surveillance of schistosomiasis transmission risk in Sichuan Province from 2020 to 2024, with 409.27 hm2 areas found with snails, and a total of 97 877 snails were captured, with no S. japonicum infection identified in snails using microscopy. Conclusions　From 2020 to 2024, the epidemic situation of schistosomiasis in Sichuan Province showed an overall downward trend, the schistosomiasis control achievements were continuously consolidated; however, the sensitive and highly efficient schistosomiasis surveillance and early warning system requires to be improved in the future.

Key words: Schistosomiasis, Surveillance, Endemic situation, Elimination, Sichuan Province 

摘要： 目的　了解2020—2024年四川省血吸虫病监测点疫情变化趋势，为进一步推进山丘型血吸虫病流行区消除血吸虫病提供科学依据。方法　2020—2024年，选取四川省63个血吸虫病流行县（市、区）作为国家级血吸虫病监测点，将达到传播阻断或消除标准的有螺县（市、区）和无螺县（市、区）分别分为Ⅱ类监测县（市、区）组和Ⅲ类监测县（市、区）组。每个监测县（市、区）每年随机抽取2 ~ 3个行政村开展流动人群、家畜血吸虫病监测，以及螺情监测和风险监测。流动人群采用间接血凝试验（indirect hemagglutination assay，IHA）开展筛查，阳性者进一步通过尼龙绢袋集卵孵化法和改良加藤厚涂片法进行病原学检测，每个监测县（市、区）调查人数≥ 200人。在Ⅱ类监测县（市、区）全域范围内，调查≥ 100头从外地引进的家畜，采用粪便毛蚴孵化法检测家畜血吸虫感染情况。从Ⅱ类监测县（市、区）选择3个螺情较重的行政村，并从Ⅲ类监测县（市、区）随机选择3个历史螺情较重、钉螺引入风险较大或适宜钉螺孳生环境较多的行政村开展钉螺调查。选取≥ 20%的Ⅱ类监测县（市、区），每个县（市、区）随机选择2个历史螺情较重或钉螺引入风险较大或适宜钉螺孳生环境较多的行政村，每村至少选取5处环境开展钉螺和野粪调查，以监测血吸虫病传播风险。对捡获钉螺采用压碎镜检法鉴定死活，采用压碎镜检法和环介导等温扩增技术（loop⁃mediated isothermal amplification，LAMP）检测血吸虫感染情况。采用毛蚴孵化法检测野粪血吸虫虫卵污染情况。采用ArcGIS 10.4.1软件绘制活螺平均密度空间分布地图，并进行活螺平均密度的区域聚集性分析；采用热点分析法进行局部空间自相关分析。结果　2020—2024年，四川省累计对73 241名流动人群开展血吸虫病血清学筛查，检出血清抗血吸虫抗体阳性355例，累计阳性率为0.48%（355/73 241）；逐年阳性率分别为0.69%（97/14 009）、0.68%（101/14 845）、0.46%（67/14 607）、0.34%（51/14 923）和0.26%（39/14 857），2024年较2020年下降了62.32%，不同年份间血检阳性率差异有统计学意义（[χ2] = 43.530，P < 0.001）。血检阳性者粪检结果均为阴性。各年份不同地区流动人群血清抗血吸虫抗体阳性率差异均有统计学意义（[χ2] = 4.913 ~ 129.440，P均< 0.05）；2023年资阳市最高，为1.09%；其余年份均为凉山彝族自治州最高，为1.43% ~ 3.18%。2024年男性流动人群血清抗血吸虫抗体阳性率高于女性（[χ2] = 5.663，P < 0.05），其余年份不同性别阳性率差异均无统计学意义（[χ2] = 0.028 ~ 1.207，P均> 0.05）。除2023年外（[χ2] = 2.044，P > 0.05），其余年份不同职业人群血清抗血吸虫抗体阳性率差异均有统计学意义（[χ2] = 11.711 ~ 45.920，P均< 0.05），以干部职员、建筑工人、渔船民、学生阳性率较高（P均< 0.05）。各年份不同年龄组血清抗血吸虫抗体阳性率差异均有统计学意义（[χ2] = 16.523 ~ 35.616，P均< 0.05）；2023年46 ~ 55岁年龄组人群阳性率最高，其余年份均为6 ~ 15岁年龄组人群阳性率最高（P均< 0.05）。2020—2024年，四川省累计监测家畜8 316头，未发现血吸虫感染阳性家畜。2020—2024年，四川省累计查螺14 703.90 hm2，查出有螺面积1 815.92 hm2，查出有螺面积占比为12.35%（1 815.92/14 703.90）。累计捕获钉螺502 854只，未发现血吸虫感染阳性钉螺；平均有螺框出现率为6.91%（247 844/3 587 122），不同年份有螺框出现率差异有统计学意义（[χ2] = 289 707.440，P < 0.001，Cramer’s V = 0.284）。2021—2023年四川省活螺平均密度存在空间自相关，呈空间聚集模式（Moran’s I = 0.078 ~ 0.128，Z = 2.378 ~ 3.642，P均< 0.05）；2024年则呈现随机分布模式（Moran’s I = 0.049, Z = 1.622，P > 0.05）。雅安市雨城区、芦山县、荥经县，眉山市洪雅县、仁寿县，乐山市市中区，成都市大邑县、崇州市（Z = 1.982 ~ 3.223，P均< 0.05）等多个地区持续出现活螺平均密度高值聚集。2020—2024年，四川省血吸虫病风险监测工作累计查螺2 599.89 hm2，查出有螺面积409.27 hm2，共捕获钉螺97 877只，经检测均未发现血吸虫感染阳性钉螺。结论　2020—2024年四川省血吸虫病疫情总体呈下降趋势，防控成果得到持续巩固，未来仍需进一步完善敏感高效的监测预警体系。

关键词: 血吸虫病, 监测, 疫情, 消除, 四川省