马来丝虫微丝蚴定量注射感染中华按蚊和致倦库蚊的实验观察

本文报告采用改进的微量注射技术和较为精细的计数方法,以2—10条微丝蚴/蚊,定量注射感染中华按蚊和致倦库蚊,找出了这两种蚊虫的微丝蚴感染量与感染期幼丝虫阳性率、幼丝虫平均发育成熟率之间的定量关系;比较了在注射感染条件下两种蚊虫对马来丝虫易感性的差异。     

宁波市基本消灭丝虫病后期监测

宁波市辖有11个县(市)、区,总人口507万,以马来丝虫流行为主,兼有班氏和马来两种混合感染,传播媒介马来丝虫为中华按蚊,班氏丝虫为致倦库蚊。本市于1986年达到基本消灭丝虫病标准,随之转入对一周岁以上人群的监测工作。 (一)纵向监测 1.人群血检:1985～1989年共血检13119人,于1985年发现微丝蚴阳性者1例,密度为8mf/60μl,其余均为阴性。 2.蚊媒解剖:在蚊虫生长高峰季节,捕检帐内吸血中华按蚊8228只,解剖淡色库蚊、致倦库蚊5040只,均未发现阳性蚊虫。 3.血清学监测:采用IFAT检测,以≥1∶20以     

嗜人按蚊对班氏丝虫易感性的实验观察

本文报告嗜人按蚊对班氏丝虫人工感染的易感性,并和中华按蚊、致倦库蚊和东乡伊蚊的易感性进行比较。在用一名微丝蚴密度为190条/20cmm的班氏微丝蚴血症者血液感染的188只嗜人按蚊、202只中华按蚊、280只致倦库蚊和129只东乡伊蚊中,L_3阳性率分别为35.64％、9.41％、30.0％和65.89％;而在用另一名微丝蚴密度为83条/20cmm的班氏微丝蚴血症者血液感染的188只嗜人按蚊、134只中华按蚊、289只致倦库蚊和176只东乡伊蚊中,L_3阳性率分别为18.09％、3.73％、13.84％和39.77％。结论认为,嗜人按蚊对班氏丝虫人工感染的易感性明显高于中华按蚊,明显低于东乡伊蚊,而与致倦库蚊的易感性处在同一水平上。     

非丝虫病流行区的致乏库蚊对城市型班氏丝虫的敏感性研究

作者以采自无班氏丝虫流行的印尼雅加达东郊贝卡西和西郊唐格朗两地的致乏库蚊蛹期及来自曼谷、台北、西贡的蚊卵和幼虫,分别在实验室内饲养,给羽化后3～4天的雌蚊饲以班氏微丝蚴血症(8～32条/20立方毫米)者的血液。吸血后将未感染雌蚊的子代,如上法饲以同一供血者的血液进行累代选育。弃去吸血后4天内死亡的蚊虫,对以后死亡的蚊虫作解剖检查有无发育中的幼丝虫。至吸血后7～9天杀死存活的蚊虫,解剖观察幼丝虫的发育情况,该时蚊体内的幼丝虫为易于识别的Ⅱ期幼丝虫。凡有发育的幼丝虫存在的为敏感的蚊虫。     

广东省基本消灭丝虫病后媒介传播作用的研究

1988～1992年连续5年对蚊媒进行纵向监测观察，各年致倦库蚊的自然感染率分别为0．11％、0．03％、0．03％、0．01％和0．01％，呈逐年下降的趋势，且仅在前3年有发现感染期幼虫；而中华按蚊则未发现自然感染蚊只。每年计算致倦库蚊的年传播潜势分别为350．48、186．92、186．92、0和0，均未达到起传播作用的量。横向监测，1992～1996年在原流行区40个县市119个乡镇的225个管理区共解剖致倦库蚊117404只，中华按蚊1256只，均未发现人体丝虫感染。结果表明广东省丝虫病的传播已完全被阻断。     

不同日龄致倦库蚊对马来丝虫易感性的比较研究

不同日龄致倦库蚊分别经胸内接种马来丝虫微丝蚴后,比较观察了蚊虫体内微丝蚴的黑化率、(?)虫率以及感染性蚊虫的比率。接种后第3、4、5、9d解剖接种蚊虫,结果表明,1～2日龄蚊虫体内微丝蚴黑化率显著高于15～16日龄蚊虫,分别为84.1％和57.5％。三期幼虫率则相反,分别为1.5％和3.7％。黑化的微丝蚴主要分布在蚊虫腹部,占72.3％和69.1％。     

广东基本消灭丝虫病后的远期监测

广东基本消灭丝虫病后，于１９８８～１９９３年进行丝虫病的纵向监测和横向监测，结果，９个纵向监测县１９８８，１９９０和１９９２年人群微丝蚴率分别为０．１２％，０．１０％和０．０６％，５年致倦库蚊自然感染率分别为０．０７％，０．０２％，０．０３％，０．０１％和０．０１％，１９９１年和１９９２年未发现感染期幼虫，中华按蚊均未发现幼丝虫感染，人群微丝蚴率及致倦库蚊自然感染率均呈下降趋势，１９９０年和１９９     

班氏丝虫微丝蚴周期性与致倦库蚊吸血和传播的观察

我国流行的班氏丝虫为夜现周期型,致倦库蚊和淡色库蚊为主要传播媒介,微丝蚴(mf)在外周血液中周期性出现的机理虽然有不少学说,至今未完全阐明。我们在贵州省思南县华溪沟村对12例班氏mf血症者的mf在人体外周血液中出现的时间与当地传播媒介致倦库蚊叮人吸血活动规律,以及不同mf密度患者对致倦库蚊幼丝虫的感染情况等有关参数进行观察,结果如下。     

致倦库蚊(海地株)感染班氏丝虫的媒介能力

致倦库蚊是班氏吴策线虫的重要媒介之一,但其媒介能量因地理区域而有差异。这种差异究竟是由蚊株还是丝虫株的不同所造成,目前尚不清楚。为测定海地株致倦库蚊和班氏丝虫株组合的媒介能量,作者进行了以下试验:(1)在实验室控制条件下蚊对班氏微丝蚴(mf)的摄入量。(2)mf移行到胸肌的时间和在胸肌滞留的时间.(3)摄入mf发育为第3期幼虫(L_3)的比例。实验用蚊为海地Leogane株致倦库蚊第40～44代。含mf的虫血采自经常到海地旅行的感染者;按Lowrie(1983)的方法     

云南楚雄2014年蚊媒及其病毒感染调查

目的了解云南楚雄元谋、武定和双柏3县蚊虫及其主要虫媒病毒种类,为制定出有效的虫媒传染病防控对策提供依据。方法2014年6-7月采用诱蚊灯在调查点通宵捕捉蚊虫,对现场采集蚊虫进行形态分类鉴定;采用C6/36细胞培养法和RT-PCR扩增目的基因片段对蚊虫体内病毒进行分离、鉴定。结果共捕获4属15种12 384只蚊虫,三带喙库蚊、中华按蚊、致倦库蚊和微小按蚊分别占捕获蚊虫总数的59.95%、19.31%、10.90%和 4.13%;C6/36细胞培养处理116组蚊虫,其中29组发生细胞病变,经基因鉴定为版纳病毒(BAV)、Totivirus 病毒(TOV)、乙型脑炎病毒(JEV)和Nam Dinh病毒(NDiV)4种,其中,三带喙库蚊的JEV、BAV、TOV和NDiV基因扩增批阳性率分别为1.87%、11.32%、3.77%和9.43%;希氏库蚊的NDiV基因扩增批阳性率为25.00%;致倦库蚊和中华按蚊的BAV、NDiV批阳性率分别为20.00%、33.34% 和5.00%、7.50%。结论楚雄地区蚊虫种类多,且以三带喙库蚊和中华按蚊为优势蚊种,从两种蚊虫标本中能分离到JEV、TOV、BAV和NDiV病毒,表明调查地区发生乙脑及其它虫媒病毒性疾病流行的危险较大。     

注射感染马来丝虫微丝蚴在蚊虫体内早期...

This paper reports the early development and variation of inoculated Brugia malayi microfilariae in 3 groups of mosquitoes, i. e. young Anopheles sinensis, young Culex quinquefasciatus and old Cx. quinquefasciatus. Significant differences were observed among these groups. Sixty hours after inoculation, the percentage of normally developing filarial larvae in young An. sinensis was 72.3%; the percentage of melanized microfilariae in young Cx. quinquefasciatus was 75.4% and the percentage of filarial larvae which developed abnormally or remained in diapause status in old Cx. quinquefasciatus was 67.1%, each being much higher than that in the other groups. It was suggested that the immune competence of the mosquitoes had influence upon the filarial development. The intensity of the immune response not only varied with the species, but also diminished with the aging of mosquitoes.     

Quantitative studies on the development of inoculated Brugia malayi microfilariae in Anopheles sinensis and Culex quinquefasciatus

Definite numbers of B. malayi mf were inoculated into An. sinensis and Cx. quinquefasciatus, and their subsequent development was observed. The relationships between the dosage and the L3 positive rate on the one hand and the average filarial maturity rate on the other were defined. At the same dosages of 4 and 10 mf/mosquito, the L3 positive rates and the average filarial maturity rates in An. sinensis were much higher than those in Cx. quinquefasciatus (p less than 0.01). It was demonstrated that the immune response to filariae of the mosquitos was the main factor resulting in these differences. The intensity of the immune response not only varied with the species, but also declined with the aging of mosquitos. The results of our experiment might be useful to studies on the dynamics of filariasis transmission and the interaction between filariae and their insect hosts.     

马来丝虫微丝蚴定量注射感染中华按蚊和致倦库蚊的...

With an improved technique, quantitative inoculation of Brugia malayi microfilariae (mff) into Anopheles sinensis and Culex quinquefasciatus was carried out in our laboratory in 1988. The development of B. malayi mff in these two species of mosquitoes was observed. In the system of B. malayi and An. sinensis, a well-fitted linear correlation appeared between the number of mff inoculated and the infective larva (L3) positive rate (r = 0.9910; P less than 0.01). The regression equation with the regression coefficient of 8.490 suggested a high susceptibility of this species of mosquito to B. malayi even under the condition of experimental inoculation. The quantitative relationship between the number of mff inoculated and the average filarial maturity rate was also exhibited. At the same dosages of 4 and 10 mff/mosquito, the L3 positive rates and the average filarial maturity rates in An. sinensis were much higher than those in Cx. quinquefasciatus (P less than 0.01), indicating significant difference occurred inside the bodies of these two species of mosquitoes.     

Development of Wuchereria bancrofti in Culex quinquefasciatus that survived the exposure of sub-lethal dose of Bacillus sphaericus as larvae

Development of Wuchereria bancrofti in Culex quinquefasciatus emerged from the larvae that survived the exposure of sub-lethal dose of Bacillus sphaericus was examined in the laboratory. Third instar larvae of Cx. quinquefasciatus were treated with B. sphaericus at a sub-lethal dose of 11.35 microg/250 ml. The female mosquitoes that emerged from the survived larvae were fed on microfilaraemic human blood and parasite development was monitored in the fed mosquitoes. Both treated and untreated mosquitoes could ingest microfilaria (mF) equally as there was no significant difference in mF density between them. But, density of developmental stages of the parasite in treated group was significantly lower. Since, there was no mortality of mosquitoes, the lower density of the developmental stages could be attributed to the loss of parasites in the treated mosquitoes. Consequently, the proportion of mosquitoes with infective larvae (L3) and number of L3 were also significantly lower in treated females. Delay in parasite development was also noticed in treated mosquitoes. The present study indicates that B. sphaericus, when applied at sub-lethal dose kills larvae, and in addition, inhibits development of the filarial parasite and consequently reduces L3 yield in adult mosquitoes that emerged from the survived larvae.     

Transmission of bancroftian filariasis in tea agro-ecosystem of Assam, India

Tea industry is a labor intensive agro-industry and filariasis is mostly localized among the tea garden workers in Assam. The workers live inside the gardens in colonies. Studies conducted in two cosecutive years revealed that among the host seeking Culex quinquefasciatus average infection rate was 4.6% and with 2.1 larvae per mosquito. The overall prevalence of infective mosquitos was 0.8% with average L3 load of 2.0 per mosquito. The probability of infected mosquitos surviving to have complete development of filarial larvae (13 days) was 0.17. The expectation of infective life was 1.416 days for man biting Cx. quinquefasciatus and the estimated adult survival rate of was 87.6%. It has been estimated that a total of 22,569 mosquito bites were received/man/year in tea garden environment out of which 182 bites/man/year were infective (0.806%). The monthly biting rate varied from 310-4,758.5 bites per man (mean 1,846 +/- 1,389.7 SD). Monthly transmission index of W. bancrofti filaria showed two periods of transmission. In both the year no infection was detected during February and March and infection rate remained low up to May (average infection in April 0.72% and in May 0.48%).     

Bancroftian filariasis in a Philippine village: entomological findings.

Bancroftian filariasis in an isolated Philippine village has been intensively investigated; this paper reports the entomological findings. Surveys were carried out six months apart in the driest and wettest months. Significant transmission was demonstrated only during the wet season. Aedes poicillius was the major vector of Wuchereria bancrofti. Ae. poicilius accounted for 58% of larvae found in the axils of banana plants and 31% of those in abaca axils; negligible numbers of larvae of this species were found in pandanus and gabi axils. Mosquitoes were collected from indoor harbourages twice weekly for five weeks during the wet season; 615 mosquitoes were caught of which 80% were Ae. poicilius and 9% were Culex quinquefasciatus. 11% of the former and 13% of the latter contained filariae; whereas all stages of development were seen in Ae. poicilius, no development beyond the first stage was seen in Cx. quinquefasciatus. Human bait trapping was used for 110 manhours; 371 mosquitoes were caught of which 58% were Ae. poicilius and 24% were Culex summorosus. Filarial larvae were seen only in Ae. poicilius; 3.7% of mosquitoes were positive and all stages of filarial development were seen. The mean landing/biting rate between 1900 and 0500 hours was 3.37 mosquitoes per man-hour with a maximum of almost seven mosquitoes per man-hour at midnight. Overall, 2.26% of vectors collected in the human studies were infective. There was an average of 3.38 third-stage larvae per infective mosquito. The efficiency of transmision was estimated as 6.1 x 10-5, or one new case of microfilaraemia for every 16, 400 bites by infective mosquitoes in the village population. In contrast to the human studies, large numbers of mosquitoes were caught by animal bait trapping in both the wet and dry seasons. The distribution of mosquito species was similar in the two seasons. Ae. poicillius represented only 1.0-1.5% of all mosquitoes seen. No filarial larvae were seen. It was concluded that transmission of filariasis in the village was inefficient and postulates were advanced to explain the increased intensity and severity of filariasis inmen as compared to women.     

Experimental vertical transmission of Japanese encephalitis virus by Culex tritaeniorhynchus and other mosquitoes

Vertical transmission of Japanese encephalitis virus to the F1 adult stage was demonstrated in Culex tritaeniorhynchus, Cx. annulus, Cx. quinquefasciatus, and Armigeres subalbatus. Transmission to the F1 larval stage was demonstrated in Cx. pipiens, Aedes vexans, Ae. alcasidi, and A. flavus. In Cx. tritaeniorhynchus, vertical transmission rates (the percentage of parent females transmitting to progeny) varied (12-100%). Filial infection rates (the percentage of progeny infected) for a given mosquito virus combination were markedly affected by the interval of time between parental infection and oviposition, suggesting that vertical infection was not transovarial in nature but occurred at oviposition. Filial infection rates for Cx. tritaeniorhynchus also varied widely by family and, as measured in F1 larvae, rates in excess of 20% were observed in a family. Filial infection rates in Cx. tritaeniorhynchus F1 adults were about 4 times lower than those in larvae. Japanese encephalitis virus was sexually transmitted from male to female Cx. tritaeniorhynchus.     

Field evaluation of biolarvicides in Surat city, India

BACKGROUND & OBJECTIVES: Two bacterial larvicide (bio-larvicide) formulations--Bacticide and VectoBac containing viable endospores and delta endotoxin of Bacillus thuringiensis var israelensis H-14 were evaluated in 2001 for their mosquito larvicidal efficacy under the operational conditions of urban malaria control programme in Surat city, India. METHODS: Larvicides were applied at the recommended dose in selected breeding habitats of Anopheles (An. stephensi), Aedes (Ae. aegypti) and Culex (Cx. quinquefasciatus) and reductions in the densities of III and IV instars were compared with that of untreated matched controls. RESULTS : At the construction sites in cemented tanks/chambers VectoBac produced reduction in the density of III and IV instar larvae of An. stephensi (98-100%) and Ae. aegypti (100%) in the first week of application whereas Bacticide produced 71-100% reduction in An. stephensi and 100% in Ae. aegypti. Re-application of VectoBac on Day 10 caused better control up to Day 20 when compared with Bacticide. In stagnant water pools, VectoBac produced 27.6-85.3% reduction in the larvae of An. subpictus and 18.5-83.8% in those of Cx. quinquefasciatus whereas Bacticide produced 23.3-30.3% and 39-97.2% reduction in An. subpictus and Cx. quinquefasciatus larval densities in the first week post application, respectively. Bacticide application gave better impact on Cx. quinquefasciatus larvae in the second week after re-application as compared to VectoBac. In storm water drains, VectoBac caused respectively 6.2-100% and 6.4-97.6% reduction in An. subpictus and Cx. quinquefasciatus larvae in the first week of application whereas Bacticide produced 100% and 13.3-98.8% reduction in An. subpictus and Cx. quinquefasciatus larval densities, respectively. INTERPRETATION & CONCLUSION: Both the formulations were equally effective on An. subpictus and Cx. quinquefasciatus larvae after a second application. The results showed that application of these biolarvicides would be required at 7-10 day intervals. The health workers engaged in the application of biolarvicides reported a better ease of handling and application of the liquid formulation (VectoBac) than the wettable powder formulation (Bacticide).