巢氏PCR判定西藏疟疾流行区传疟媒介

目的确定西藏墨脱县疟疾流行区的疟疾传播媒介。方法根据2005、2006和2007年疟疾发病情况,在墨脱县选择了3个疟疾发病较高的自然村,采用人诱、牛诱、灯诱及清晨人房全捕等方法捕获成蚊,经形态学鉴定后麻醉处死,密封干燥,带回实验室-20℃冻存备用,采用混合样本法随机抽取10只多斑按蚊复合体为一份混合标本,提取蚊虫DNA。根据文献采用巢氏PCR扩增疟原虫小亚单位核糖体脱氧核糖核酸(SSUrDNA),并对阳性结果克隆测序,比对证实。结果共捕获按蚊5345只,其中多斑按蚊复合体5190只,带足按蚊155只,提取的360份多斑按蚊复合体混合样本DNA中发现子孢子阳性扩增样品2份,种型鉴定2份阳性混合样本均为伪威氏按蚊,PCR产物经克隆测序,NCBIBLAST同源性比对证实为疟原虫SSurDNA基因片段。结论多斑按蚊复合体中的伪威氏按蚊为西藏林芝疟疾流行区的传疟媒介。     

西藏林芝地区墨脱县传疟媒介调查研究

目的 调查西藏林芝地区墨脱县传疟媒介,为制定针对性防制措施提供依据。 方法 2007年7～8月在墨脱县选择3个疟疾发病率较高的自然村,采用通宵/半通宵室内、外人/牛饵帐诱捕法、通宵人/牛房诱蚊灯诱捕法和清晨人房搜捕法捕蚊,对捕获的按蚊进行形态学鉴定,并进行种群组成、密度、叮人率、吸血习性、栖息习性和经产蚊比率等观察;在不同的水体捞取按蚊幼虫,进行蚊种鉴定,调查按蚊幼虫孳生环境。 结果 共捕获按蚊5 345只,经形态鉴定,只发现伪威氏按蚊、威氏按蚊和带足按蚊等3种,其中伪威氏按蚊占94.71%（5 062/5 345）,威氏按蚊与带足按蚊分别为2.39%（128/5 345）和2.90%（155/5 345）。伪威氏按蚊室内和室外的半通宵诱捕平均密度分别为17只/人和105只/人;全通宵室内和室外的人饵帐诱平均叮人率分别为15.80只/（人·夜）（79/5）和326.22只/（人·夜）（1 468/4.5）;全通宵室外人、牛饵诱捕及人、牛房诱蚊灯灯诱,伪威氏按蚊趋吸人血与牛血的比率分别为30.51%（714/2 340）和69.49%（1 626/2 340）及32.02%（57/178）和67.98%（121/178）,表明伪威氏按蚊偏吸牛血并兼吸人血;清晨人房搜捕,共捕获伪威氏按蚊7只,均为胃血未消化的饱血蚊;共捞获按蚊幼虫106条,其中伪威氏按蚊和威氏按蚊幼虫62条,带足按蚊幼虫44条,按蚊幼虫孳生的水体类型仅限于稻田。 结论 伪威氏按蚊具备在当地传播疟疾的媒介生物学条件。     

应用多重PCR法分析西藏察隅疟疾流行区按蚊吸血习性

目的用多重PCR法分析西藏疟疾流行区察隅县常见按蚊的吸血习性,为下一步研究传疟媒介提供参考。方法2011年7~8月选择察隅县不同生态环境的3个自然村(日玛村、塔玛村和京都村),每个村在人房和畜舍选择8个点,采用诱蚊灯全通宵(20∶00至次日08∶00)诱捕法捕捉按蚊,次日清晨收集诱捕的蚊虫,经形态学鉴定蚊种,分析按蚊组成。收集饱血按蚊,分别提取单只蚊胃血的DNA,采用基于不同动物mtDNA-cytb序列差异的多重PCR法鉴定各蚊胃血源,计算人血指数,分析按蚊的吸血习性。结果共捕获按蚊1 442只,经形态学鉴定,多斑按蚊种团占99.6%(1 436/1 442),带足按蚊和腹簇按蚊占0.4%(6/1442)。多斑按蚊种团中,伪威氏按蚊占85.5%(1228/1436),威氏按蚊占14.5%(208/1 436)。用多重PCR检测202只多斑按蚊种团(伪威氏按蚊188只和威氏按蚊14只)的饱血蚊胃血,结果显示,伪威氏按蚊兼吸牛/猪血和人血,人血指数为0.35,威氏按蚊吸食猪血和人血,人血指数为0.29。结论西藏察隅县2种常见按蚊(伪威氏按蚊和威氏按蚊)均兼吸人畜血,伪威氏按蚊的人血指数较高。     

西藏墨脱县疟疾暴发自然村伪威氏按蚊与威氏按蚊生态习性比较

目的 目的 调查西藏疟疾流行区墨脱县中、 高海拔地区主要按蚊伪威氏按蚊和威氏按蚊的生态习性及其传播疟疾的 潜能。 方法 方法 采用人诱、 动物诱 （牛、 马、 猪） 和诱蚊灯诱捕方法捕获成蚊, 分析按蚊密度、 夜间活动规律、 室内外吸血习性; 对于捕获的经形态学鉴定为多斑按蚊复合体的蚊虫, 按照捕蚊时间、 地点和捕蚊方式进行标记, 带回实验室后采用PCR方 法鉴定蚊种; 采用晨捕和白天搜捕法判断按蚊栖息习性; 在不同类型水体捕捞幼虫, 饲养羽化以判定孳生地。 结果 结果 共捕 获多斑按蚊复合体蚊虫1 053只, 其中伪威氏按蚊331只, 威氏按蚊722只。室内与室外威氏按蚊的数量均高于伪威氏按 蚊 （P < 0.01, P < 0.05）。室内外两种按蚊构成比差异无统计学意义 （P > 0.05）。伪威氏按蚊和威氏按蚊经产蚊比例分别为 65.90%和69.86%, 差异无统计学意义 （P > 0.05）, 伪威氏按蚊室外吸血蚊数大于室内吸血蚊数 （P < 0.05）, 威氏按蚊室内外 吸血蚊数差异无统计学意义 （P > 0.05）。两种按蚊夜间活动均为单峰分布, 威氏按蚊密度日落后21： 00-22： 00达高峰, 随 后逐步下降, 凌晨4： 00后未捕获威氏按蚊; 伪威氏按蚊密度高峰为24： 00至凌晨1： 00, 几乎整夜都有活动。结论 结论 西藏墨 脱县中、 高海拔地区威氏按蚊构成与密度均高于伪威氏按蚊, 两种按蚊生态习性有差异; 威氏按蚊比伪威氏按蚊更具传播 疟疾的潜能。     

西藏林芝地区察隅县按蚊种群调查

目的确定西藏林芝地区察隅县主要按蚊蚊种。方法2010年7-8月在察隅县选择4个自然村,采用通宵/半通宵室内、外人饵帐诱捕法和通宵诱蚊灯诱捕法捕蚊,对捕获的按蚊进行形态学鉴定。结果共捕获按蚊2 991只,其中带足按蚊2 284只(占76.36%),多斑按蚊种团667只(占22.30%),其他按蚊40只(占1.34%);带足按蚊室内、外半通宵平均密度分别为56.2只/夜和4只/夜,多斑按蚊种团室内、外半通宵平均密度分别为17.8只/夜和17.9只/夜;带足按蚊室内、外全通宵室内叮人率分别为28.1只/(人夜)和2只/(人夜),多斑按蚊种团全通宵室内、外叮人率均为8.9只/(人夜)。结论带足按蚊和多斑按蚊为察隅县优势蚊种,是可能的疟疾传播媒介。     

西藏墨脱县疟疾流行区多斑按蚊复合体种型鉴定

目的 鉴定西藏林芝地区墨脱县疟疾流行区多斑按蚊复合体的种型。 方法 墨脱县捕获的5 190只按蚊经形态学鉴定为多斑按蚊复合体后,随机取575只,酚-氯仿法提取单蚊DNA作为模板,根据伪威氏按蚊、多斑按蚊、威氏按蚊、达罗毗按蚊和塞沃按蚊分别设计5对特异性引物,PCR扩增rDNA第二转录间隔区（ITS2）片段,进行种型鉴别。对目标片段进行测序、同源性比对,并运用MEGA（3.1）软件构建多斑按蚊复合体的系统进化树。 结果 575份DNA样本中有11份扩增出约231 bp的条带,即威氏按蚊（1.9%）;564份扩增出约119 bp的条带,为伪威氏按蚊（98.1%）。 PCR种型鉴定结果与同源性比对及系统进化树的结果一致。 结论 西藏林芝地区墨脱县疟疾流行区多斑按蚊复合体由伪威氏按蚊和威氏按蚊构成,伪威氏按蚊为优势蚊种。     

西藏墨脱县多斑按蚊复合体尚未发生击倒抗性突变

目的探明西藏林芝地区疟疾流行区墨脱县多斑按蚊复合体是否发生击倒抗性突变,并获得我国多斑按蚊复合体5成员种钠离通道蛋白基因（VGSC）IIS4-S6区段基因序列信息。方法采用简并引物扩增我国多斑按蚊复合体5成员种的VGSC基因IIS4-S6区段,扩增产物双向测序拼接;PCR扩增墨脱县背崩乡、德兴乡、墨脱镇和达木乡捕获的共161只多斑按蚊复合体VGSC基因,对PCR产物双向测序,观察L1014位点是否发生突变。结果获得我国多斑按蚊复合体5成员种VGSC基因IIS4-S6区段基因序列,5成员种L1014位点均为TTA,对墨脱县的背崩乡、墨脱镇和达木乡捕获的伪威氏按蚊和威氏按蚊进行VGSC扩增并测序,均未发生击倒抗性突变。结论西藏林芝地区墨脱县多斑按蚊复合体尚未发生击倒抗性突变。     

西藏林芝地区察隅县伪威氏按蚊溴氰菊酯抗性初步调查

目的 了解西藏林芝地区察隅县按蚊优势种伪威氏按蚊对溴氰菊酯的敏感性.方法 选择察隅县下察隅镇的日玛村和塔玛村为调查点,于2011年7月采用牛诱法捕获饱血伪威氏按蚊,带回实验室繁殖至子一代,采用世界卫生组织( WHO)推荐的成蚊接触筒法对溴氰菊酯杀虫剂的敏感性进行测试,同时设立空白对照组,空白对照组和实验组测试试纸均以丙酮为溶剂,实验组为0.05％溴氰菊酯,对照组未添加杀虫剂.将待测蚊虫移入装有0.05％溴氰菊酯药膜滤纸的实验组接触筒和空白对照接触筒中,蚊虫接触供试杀虫剂60 min,计算半数击倒时间(KT50),24h后记录蚊虫死亡数,计算死亡率.结果 察隅县下察隅镇伪威氏按蚊经0.05％溴氰菊酯测试后,击倒率分别为96.4％和97.5％,校正死亡率均为100％.结论 察隅县下察隅镇伪威氏按蚊对溴氰菊酯杀虫剂敏感,可以采用溴氰菊酯对该地伪威氏按蚊进行媒介控制.     

2016-2018年安徽省传疟媒介监测

目的　了解2016-2018年安徽省传疟媒介种群分布、密度、季节消长及夜间活动规律,为消除疟疾后阶段输入性疟疾防控策略的制定提供参考。方法　2016-2018年,在安徽省105个县（市、区）采用诱蚊灯全通宵捕蚊法和室外双帐人饵全通宵诱捕法开展传疟媒介蚊种监测,比较不同时间、不同地区和不同捕蚊场所按蚊密度。结果　2016-2018年,安徽省105个县（市、区）中有103个县（市、区）捕获到按蚊,其中灯诱法捕获32 494只、人诱法捕获36 228只。所有捕获按蚊经形态学鉴定均为中华按蚊,未发现嗜人按蚊。中华按蚊密度高峰为6-8月,夜间活动高峰为19∶00-23∶00。不同捕蚊场所中,以畜禽棚按蚊密度最高（H = 18.835,P < 0.05）。2016和2017年不同地区中华按蚊密度均存在差异（H = 16.655、11.566,P均< 0.01）,淮河以北地区中华按蚊密度较低。结论　中华按蚊在安徽省广泛分布,是当前安徽省最主要的传疟媒介。在消除疟疾后阶段,应加强安徽省媒介监测,在疫点及时采取媒介控制措施,防止出现境外输入性疟疾本地再传播。     

PCRRFLP单酶切法鉴别赫坎按蚊复合体的研究

目的建立一种新的赫坎按蚊复合体近缘种按蚊基因鉴别技术,应用于现场按蚊样本的鉴别。方法用分子生物学软件Vector NTI 9.0,对赫坎按蚊复合体的嗜人按蚊、雷氏按蚊、中华按蚊、八代按蚊4个近缘种按蚊rDNA基因的ITS2区段序列进行限制性内切酶酶切位点预测分析,选择特异性内切酶,建立一种能同时鉴别4种近缘种按蚊的聚合酶链反应限制性片段长度多态(PCR RFLP)单酶切法鉴别技术,并对现场捕获的452只按蚊样本进行基因鉴别。结果软件预测赫坎按蚊复合体近缘种4种按蚊的rDNA基因的ITS2区段可被限制性内切酶Dde I切成大小易于区分的不同片段,PCR RFLP单酶切实验结果和软件预测结果完全吻合。4个疟疾流行区捕获的452只按蚊样本经PCR RFLP Dde I单酶切法鉴定有20只嗜人按蚊、6只雷氏按蚊、391只中华按蚊、35只八代按蚊,与形态学鉴别结果符合率为93.4%,与PCR RFLP双酶切法结果符合率为100%。结论新建立的PCR RFLP Dde I单酶切法基因鉴别技术可准确鉴别赫坎按蚊复合体,比传统的形态学鉴别更为简便、可靠,适合用于复合媒介地区的媒介监测。     

Efficacy of diurnal BG-Sentinel traps to capture nocturnal adult Armigeres subalbatus mosquitoes and impact of altitudinal variations in forests

Objective: To establish an efficacious and efficient surveillance method of Armigeres(Ar.) subalbatus, a known filarial vector, surviving in forest habitats to estimate realistic population density and assess the impact of altitudinal variations on the efficacy of the trap. Methods: In the study, 12 locations in areas with an altitudinal range from 82 m to 920 m were selected in three reserve forests for night sampling of adult Ar. subalbatus mosquito using standard chemical lure based BG-Sentinel traps and CDC-light traps in pairs. Effects of locations and time were estimated on the efficacy of traps as mosquito density using multifactor analysis of variance for significant differences. Impact of altitudinal variations on the efficacy of traps was assessed using multiple regression with slope comparison.Results: BG-Sentinel trap collected significantly more adult Ar. subalbatus, 4.43 folds in Gorumara NP, 5.19 folds in Neora Valley NP and 12.10 folds in Mahananda WLS than the CDC-light trap irrespective to locations. BG-Sentinel traps were tolerant of altitudinal variations(80 m-170 m) and showed no significant relationship between density and altitudes in contrast to CDC-light traps which showed a significant negative impact on capturing efficacy with increase in altitudes(P0.001).Conclusions: The study suggests that BG-Sentinel traps can be used effectively and efficiently to collect more Ar. subalbatus mosquitoes during night time in comparison to CDC-light trap under complex climatic conditions of forest and variable altitudes.     

中华按蚊吸血趋性和吸血前后活动情况的观察

目的观察中华按蚊吸血趋性和吸血前后活动情况,为改进灭蚊措施,提高防制效果提供依据。方法利用室外人、牛饵帐诱捕法进行中华按蚊吸血趋性观察,采用实验小屋法观察蚊虫吸血前后活动情况。结果室内人饵帐捕获中华按蚊约是室外捕蚊数的2.99倍,差异有统计学意义(χ2=15.12,P<0.01);室内外牛饵帐诱捕蚊数相近,差异无统计学意义(χ2=0.69,P>0.05)。牛房傍晚3h的捕蚊数为白天栖息该室内蚊虫数的12.59倍,在室内吸血前后停息1~10min者约占50%,停息30min以内者占80%以上,差异均有统计学意义(P<0.05);停息60min以上者仅占10%,差异无统计学意义(P>0.05)。结论中华按蚊具有偏外栖性,这是滞留喷洒杀灭效果不理想的重要原因。基于其吸血前后室内短暂停留的行为习性,应选用无驱避性且具有熏杀作用的速效高效杀虫剂杀灭室内中华按蚊。     

嗜血习性同域分化的中华按蚊种群rDNA-ITS2序列分析

目的 目的 探讨同域分布而嗜血习性不同的中华按蚊种群是否存在基于rDNA?ITS2序列差异的遗传分化。方法 方法 在中华按蚊密度高的自然村和按蚊孳生地之间, 同时设人饵和牛饵帐通宵诱捕大量野外按蚊种群; 经过形态鉴定分离两 组中华按蚊, 并带回实验室常规饲养。选择一温湿度适宜的大型封闭温室作为雌蚊标记?释放?重捕技术的场所, 将以上 人饵组和牛饵组中华按蚊分别经红色和黄色荧光粉标记后在温室的中间一起释放, 同时在温室两端分别设人饵帐和牛 饵帐再次诱捕 （重捕） 中华按蚊。将两次均被人饵帐和牛饵帐诱捕的中华按蚊雌蚊分成嗜人血组和嗜牛血组, 带回实验 室饲养传代, 并分别饲以其蚊虫人血和牛血。两组中华按蚊的子1代雌蚊再次使用上述标记?释放?重捕技术, 筛选嗜人 血和嗜牛血的中华按蚊品系; 并对该两品系的中华按蚊rDNA?ITS2基因进行PCR扩增测序比对。结果 结果 野外亲代嗜人 血组中华按蚊人饵帐和牛饵帐的重诱捕比例分别为54.07% （339/627） 和45.93% （288/627）, 嗜牛血组牛饵帐和人饵帐的 重捕比例分别为58.01% （409/705） 和41.99% （296/705）, 两组亲代嗜血习性均趋向选择原吸血宿主 （χ2 =19.42, P < 0.01）。子1代嗜人血组中华按蚊人饵帐和牛饵帐的重捕比例分别为63.43% （765/1 206） 和36.57% （441/1 206）, 嗜牛血组 牛饵帐和人饵帐的重捕比例分别为68.22% （1 039/1 523） 和31.78% （484/1 523）, 两组蚊虫群体嗜血习性有更显著的选择 原吸血宿主的特性 （χ2 =271.69, P < 0.01）, 表现出遗传分化现象。但PCR扩增测序比对结果显示, 两品系蚊虫的rDNA? ITS2基因碱基序列无差异, 均为469 bp。结论 结论 嗜血习性不同的中华按蚊同域种群未发生基于rDNA?ITS2序列的遗传 分化。     

How does an Ethiopian dam increase malaria? Entomological determinants around the Koka reservoir

Objectives To identify entomological determinants of increased malaria transmission in the vicinity of the Koka reservoir in Central Ethiopia. Methods Larval and adult mosquitoes were collected between August 2006 and December 2007 in villages close to (<1 km) and farther away from (>6 km) the Koka reservoir. Adult mosquitoes were tested for the source of blood meal and sporozoites. Results In reservoir villages, shoreline puddles and seepage at the base of the dam were the most productive Anopheles‐breeding habitats. In villages farther from the dam (control villages), rain pools were important breeding habitats. About five times more mature anopheline larvae and six times more adult anophelines were found in the villages near the reservoir. Anopheles arabiensis and Anopheles pharoensis were the most abundant species in the reservoir villages throughout the study period. The majority of adult and larval anophelines were collected during the peak malaria transmission season (September–October). Blood meal tests suggested that A. arabiensis fed on humans more commonly (74.6%) than A. pharoensis (62.3%). Plasmodium falciparum‐infected A. arabiensis (0.97–1.32%) and A. pharoensis (0.47–0.70%) were present in the reservoir villages. No P. falciparum‐infected anophelines were present in the control villages. Conclusions The Koka reservoir contributes to increased numbers of productive Anopheles‐breeding sites. This is the likely the cause for the greater abundance of malaria vectors and higher number of malaria cases evidenced in the reservoir villages. Complementing current malaria control strategies with source reduction interventions should be considered to reduce malaria in the vicinity of the reservoir.     

2020—2021年焦作市传疟媒介种群及密度监测结果分析

目的 了解焦作市消除疟疾后传疟媒介种群及密度情况,为消除疟疾后传疟媒介的控制和输入性疟疾再传播风险评估提供科学依据。方法 2020—2021年选择焦作市共7个县（市、区）作为传疟媒介监测点,使用诱蚊灯法及人帐诱法开展种群及密度监测,挑选大中型水体环境共20处,采用勺捕法开展蚊虫孳生地调查。结果 7个县（市、区）中除解放区外均捕获有中华按蚊。2020年媒介种群监测共捕获蚊虫8 116只,其中中华按蚊构成比为21.76%,修武县捕获中华按蚊数量最多（1 262只）,沁阳市捕获中华按蚊构成比最高（40.39%）;室内环境中中华按蚊数量多,而室外环境中中华按蚊构成比高;密度监测共捕捉蚊虫802只,平均密度为30.55只/人·小时,其中中华按蚊136只,平均密度为5.18只/人·小时;在稻田环境中捕获按蚊孑孓126条,其余水体未发现。2021年种群监测捕捉蚊虫10 852只,中华按蚊构成比为1.67%,修武县捕获中华按蚊数量最多（179只）,构成比最高（1.99%）;室内环境捕获中华按蚊数量及构成比均高于室外环境;密度监测共捕获蚊虫3 662只,平均密度为130.79只/人·小时,其中中华按蚊1...     

Changing scenario of malaria in central India, the replacement of Plasmodium vivax by Plasmodium falciparum (1986-2000)

OBJECTIVES: Since 1986, we have been studying the changing epidemiology of malaria in a forest belt of Mandla, which has the highest number of malaria cases in central India (Madhya Pradesh) to define the epidemiological characteristics of the infection with each Plasmodium species in different seasons of the year. Our long-term objective was to determine the dynamics of Plasmodium vivax vs.P. falciparum infections. METHODS: Five villages underwent fortnightly surveillance of fever cases. Drugs were distributed within 24 h after results of blood smears became available as per Indian National Anti-Malaria Programme. Indoor resting mosquitoes were also collected fortnightly. RESULTS: The only two Plasmodium species encountered were P. vivax and P. falciparum in both children and adults. Relatively more malaria infections were recorded in children (< or =14 years) than adults (>14 years) (chi2=89.94, P<0.00001). However, there were significant falling trends in P. vivax from 1986 to 2000 in both age groups (< or =14 years from 63 to 13, P<0.0001 and >14 years from 84 to 7, P<0.0001). The indoor resting density of Anopheles culicifacies, an efficient vector resistant to both dichlorodiphenyltrichloroethane (DDT) (4%) and hexachlorocyclohexane (HCH) (0.4%), was very high throughout this period in all villages (52.35 +/- 31.8, range 5-200 per man hour). Anopheles fluviatilis was present in small numbers 0.78 +/- 1.24 (range 0-7 per man hour). CONCLUSION: Major contributors of the changing epidemiology of malaria in this area are changing drug sensitivity along with insecticide sensitivity.     

Wash-resistance and field evaluation of alphacypermethrin treated long-lasting insecticidal net (Interceptor) against malaria vectors Anopheles culicifacies and Anopheles fluviatilis in a tribal area of Orissa, India

A field trial was conducted on the efficacy of Interceptor nets—a long-lasting insecticidal net (LLN) factory treated with alphacypermethrin 0.667% (w/w) corresponding to 200 mg/m², against malaria vectors Anopheles culicifacies and Anopheles fluviatilis in one of the highly endemic areas of Orissa. The study area comprised 19 villages which were randomized into three clusters and designated as Interceptor net cluster, untreated net cluster, and no net cluster. Baseline studies showed that both the vector species An. culicifacies and An. fluviatilis were 100% susceptible to alphacypermethrin. Results of wash-resistance and bio-efficacy of Interceptor nets showed 100% mortality in An. culicifacies and An. fluviatilis even after 20 washings. Bioassays on the Interceptor nets while in use in the field conditions showed a knockdown effect on 70-90% mosquitoes during different months of intervention after 3 min of exposure and 100% mortality was recorded after 24 h of recovery period. The median knockdown time for these species ranged between 4.10-5.25 min and 4.00-5.00 min respectively during intervention period. In Interceptor net study area, there was a significant reduction of 88.9, 96.3 and 90.6% in the entry rate of An. culicifacies, An. fluviatilis and other anopheline species respectively with an over all reduction of 87.5% in total mosquitoes. The overall feeding success rate of mosquitoes in the trial villages was only 12.8% in comparison to 35.0 and 78.8% in villages with untreated nets and no nets respectively. A significant reduction was also recorded in parity rate and human blood index of vector species in Interceptor net area. The results of the study showed that Interceptor nets are effective against the malaria vectors and may be used as a suitable intervention strategy in high-risk areas.