2020年长江中下游地区洪涝灾害后血吸虫病传播风险评估

Risk assessment of schistosomiasis transmission along the middle and lower reaches of Yangtze River after flooding in 2020

目的评估2020年长江中下游地区洪涝灾害对血吸虫病传播的影响。方法于2020年10月对湖南、湖北、江西、安徽和江苏等5省开展钉螺血吸虫感染情况和钉螺孳生环境污染情况调查。根据历史疫情和受灾情况,每省抽取2个县(市、区)开展调查,分别为湖南省南县、华容县,湖北省汉川市、黄石市阳新县,江西省庐山市、九江市濂溪区,安徽省池州市贵池区、枞阳县,江苏省南京市六合区、扬州市邗江区。每县(市、区)抽取2个乡(镇),每个乡(镇)抽取1个行政村作为调查村。采用系统抽样结合环境抽查法对2017—2019年查出人、畜活动频繁的有螺环境及本次受洪灾波及的历史无螺环境或达到无螺状态20年以上的环境开展钉螺调查。采用环介导等温扩增技术(LAMP)对捕获的钉螺进行血吸虫感染情况检测。在开展钉螺调查的环境中同时开展野外粪便(简称野粪)的调查,采集全部野粪并用毛蚴孵化法进行检测(一粪三检)。对钉螺和野粪的分布情况进行描述性分析,计算活螺框出现率(活螺框数/调查框数)、活螺平均密度(系统抽样活螺数/系统抽样调查框数)。采用卡方检验比较现有钉螺孳生环境中环境抽查和系统抽样法之间以及不同地区之间活螺框出现率的差异。结果共调查64处现有钉螺孳生环境,捕获钉螺8904只,其中活螺7918只。总活螺框出现率为11.7%(1813/15464),其中环境抽查活螺框出现率为10.5%(679/6441),系统抽样活螺框出现率为12.6%(1134/9023),二者差异有统计学意义(χ^(2)=14.91,P<0.01)。安徽枞阳县和贵池区系统抽样活螺框出现率分别为60.2%(607/1008)和28.4%(251/882),均较其他县高(P<0.01)。安徽省枞阳县和贵池区的活螺平均密度分别为2.177只/0.1 m^(2)和3.323只/0.1 m^(2),约为其他调查点10倍以上。LAMP法检测到1份采自安徽省贵池区钉螺的血吸虫阳性样品。在47处钉螺孳生环境中共检获野粪100份,其中血吸虫毛蚴孵化阳性野粪3份,均为牛粪,分布于江西省庐山市的2个环境和安徽省贵池区的1个环境。共调查44处本次洪灾波及的历史无螺环境或达到无螺状态20年以上的环境,采集钉螺572只,其中活螺550只。安徽贵池区(1处环境)和江西庐山市(2处环境)在潜在扩散区中发现钉螺,系统抽样活螺框出现率分别为21.2%和4.5%,活螺平均密度分别为1.254只/0.1 m^(2)和0.081只/0.1 m^(2)。LAMP法检测到2份采自江西省庐山市的钉螺血吸虫阳性样品。结论2020年洪涝灾害可能增大长江中下游地区血吸虫病的传播范围,安徽省及江西省的血吸虫病传播风险较前一年有所升高。

Objective This study aimed to assess the transmission risk of schistosomiasis along the middle and lower reaches of Yangtze River after flooding in 2020.Methods Snail survey and survey for contamination with wild feces in snail breeding environment were conducted in Hunan,Hubei,Jiangxi,Anhui,and Jiangsu Provinces in October,2020.According to the historical epidemic of schistosomiasis and the flooding record,two counties of each province were selected for this study,including Nanxian,Huarong,Hanchuan,Yangxin,Lushan,Lianxi,Guichi,Zongyang,Luhe,and Hanjiang.Two townships(town)were selected from each county,and then one administrative village was selected from each township(town)for the survey.Using systematic sampling and environmental sampling method,snail survey was performed in two categories of environment in the current flood-affected area,including snail-infested environment bearing frequent human and animal activities in 2017—2019,and in environment of historically snail-free or snail-free over 20 years.All the collected snails were examined for schistosome infection by loop-mediated isothermal amplification(LAMP)method.During collecting snails from environments,wild feces were collected as well and tested by miracidia hatching method(one sample,triple detection).Chi-square test is used to compare the difference of occurrence rate of frames with living snails surveyed using systematic and environmental sampling methods.Results A total of 64 snail breeding environment sites were surveyed,from where 8904 snails were collected,of them 7918 were alive.The overall occurrence rate of living snail frames was 11.7%(1813/15464),and the rates were 10.5%(679/6441)using environmental sampling method and 12.6%(1134/9023)using systematic sampling method.The difference between the two rates was statistically significantly(χ^(2)=14.91,P<0.01).The occurrence rates of living snail frames by systematic sampling in Zongyang and Guichi of Anhui Province were 60.2%(607/1008)and 28.4%(251/882),respectively,which were both significantly higher than the rates in other counties(P<0.01).The average density of live snails in Zongyang(2.177/0.1 m^(2))and Guichi(3.323/0.1 m^(2))were over ten folds higher than those in other counties.One sample collected from in Guichi was found schistosome positive detected by LAMP method.A total of 100 wild feces samples were collected from 47 snail breeding environment,three of them were found schistosome positive,which belong to cattle,located in two environments in Lushan,Jiangxi and one environment in Guichi,Anhui.A total of572 snails were collected from 44 sites of historically snail-free environment and the environment of snail-free for over 20 years,and 550 living snails were detected.These snails were found in the potential spreading areas in one environment in Guichi,Anhui,and two environments in Lushan,Jiangxi,with the average occurrence rates of living snail frames by systematic sampling being 21.2%and 4.5%respectively,showing the average densities of living snails being 1.254/0.1 m^(2) and 0.081/0.1 m^(2) respectively.Two samples collected from Lushan,Jiangxi were detected as schistosome positive by LAMP.Conclusion The flooding in 2020 may expand the schistosomiasis transmission areas in middle and lower reaches of Yangtze River,among them the transmission risk in Anhui and Jiangxi Provinces rose,compared to the previous year.