A longitudinal study of Japanese encephalitis in suburban Bangkok, Thailand

A one-year study of Japanese encephalitis (JE) in a small focus of transmission was conducted in suburban Bangkok in 1985. Monthly data were collected on weather, vector density, sentinel pig and chick JE antibody seroconversions, and epidemiology as related to human JE cases. The primary vector species were found to be Culex gelidus and Culex tritaeniorhynchus; from which one isolate each was obtained in March and June, respectively. Pig JE antibody seroconversion peaked in April (the hottest month), with secondary peaks following in July and December. Chick seroconversions were found only in June and July. Human cases (7) in the primary focus occurred from May-July, and started 2 months following the finding of the first JEV isolate in mosquitoes and 1 month following mass JEV seroconversion in pigs. Overall, the attack rate in the focus (0.83/10(5] was greater than 4 times that of the rest of Bangkok (0.19/10(5]. Attack rates were highest in 0-9 and 10-19 year-old groups, respectively. Indications are that JEV is transmitted to humans in Bangkok at least 10 out of 12 months per year, but that cases are concentrated in the May to July period.     

Short report: observations on the multiple feeding behavior of Culex tritaeniorhynchus (Diptera: culicidae), the vector of Japanese encephalitis in Kerala in southern India

A study was undertaken in villages endemic for Japanese encephalitis (JE) in Kerala in southern India during the period 1998-2001 to determine the host-feeding pattern of Culex tritaeniorhynchus, the major vector of JE in southeast Asia. A total of 3,067 blood-engorged Cx. tritaeniorhynchus were tested and 2,553 (82.2%) of the samples could be identified. Culex tritaeniorhynchus had fed mainly (56.6%) on cattle. Pig feeding accounted 6.3% of the total samples. Some samples (n = 980, 38.3%) were of serologic mixed origin. Of 980 mixed blood-fed mosquitoes, 975 (99.5%) had imbibed blood from two distinct hosts and 5 (0.5%) imbibed blood from three distinct hosts. Mixed blood meals were mostly (96.7%) from cattle and goats. The epidemiologic implications of multiple feeding of Cx. tritaeniorhynchus on dampening (dead-end) hosts such as cattle and goats in the transmission of JE virus is discussed.     

Impact of weather variables on mosquitoes infected with Japanese encephalitis virus in Kurnool district, Andhra Pradesh

ObjectiveTo assess the virus infection in mosquitoes during different seasons and correlated with various climatic factors.MethodsThe field collected vectors were screened for Japanese encephalitis (JE) virus after dessication using ELISA method. Most of the positive pools were recorded from Culex tritaeniorhynchus (Cx. tritaeniorhynchus) and Culex. gelidus (Cx. gelidus) during JE transmission season (winter) and some positive pools were also reported during non JE transmission periods (i.e. summer and rainy seasons).ResultsThe minimum infection rates (MIR) of 1.75 from Cx. tritaeniorhynchus and 0.17 from Cx. gelidus has been reported in the year 2002 at the beginning of the study and the values were found nil at the end of the study (2006) from the study areas of Kurnool district.ConclusionsFrom this study it is noted that MIR of Cx. gelidus and Cx. tritaeniorhynchus were modulated by various meteorological parameters. The mosquito vector abundance increases after the monsoon period (winter) and lowest in dry season (summer). Similarly, MIR fluctuated between seasons with higher MIR recorded after monsoon period and lower in the rest of season. Impact of these metrological parameters in JE virus infected mosquitoes is discussed in this paper.     

Correlation of population indices of female Culex tritaeniorhynchus with Japanese encephalitis viral activity in Kapuk, Indonesia

Nineteen consecutive monthly light trap collections of mosquitoes were made between October 1978 and April 1980 in Kapuk, Indonesia. Kapuk is a small suburb of Jakarta where pigs are raised in close proximity to rice paddies which are breeding sites for Culex tritaeniorhynchus. Japanese encephalitis (JE) virus is believed to be endemic and has been recovered from mosquitoes and pigs in the area on several occasions. A total of 18,435 female Cx. tritaeniorhynchus were allocated to 359 pools of approximately 50 per pool. Virus isolations were attempted in both Vero and BHK-21 cells and agents producing cytopathic effect were identified in a micro-neutralization test. Nineteen strains of JE were recovered from the 359 pools of Cx. tritaeniorhynchus tested. The light trap index of female Cx. tritaeniorhynchus (X) and the relative frequency of pools positive for JE (Y) for each month of the study were plotted and correlation coefficients (r) calculated after transforming the mosquito population data logarithmically and the relative frequencies of isolation by arcsine square root. The close fit of the data (p less than 0.001) to an inverse linear model (1/y = a + b log10X) suggests a close dependence of JE viral activity on the population dynamics of Cx. tritaeniorhynchus. Three additional strains of JE were recovered from other Culex spp. at the same study site. One strain each was isolated from individual pools of Cx. gelidus, Cx. vishnui and Cx. fuscocephala. Cx. tritaeniorhynchus was more frequently infected with JE than the other species tested.     

云南省乙型脑炎几个重要流行区的传播媒介调查

目的了解云南省乙型脑炎重要流行区传播媒介种群密度和地区分布。方法现场CDC诱蚊灯诱捕成蚊;吸蚊管人工捕蚊2种方法调查。结果CDC诱蚊灯诱捕成蚊法调查了5个县,捕获蚊虫6属37种8023只,其中思茅6属34种6786只,三带喙库蚊占49.01%;麻栗坡、马关、砚山、邱北、捕获蚊虫6属21种1237只,其中三带喙库蚊占71.06%;人工捕成蚊法调查了7个地区,捕获蚊虫5属21种11301只,其中思茅翠云区调查4个乡(镇)捕获蚊虫5属21种10482只,三带喙库蚊占64.44%,其它6个地区捕获蚊虫4属16种819只,乙型脑炎主要传播媒介三带喙库蚊景谷占49.13%,孟连占46.15%,陇川占35.59%;结论调查结果显示:这些地区乙型脑炎疾病传播媒介品种较多,特别是三带喙库蚊在乙型脑炎流行区种群大密度较高,地区分布较广,大量危险因素存在。     

云南景东县乙型脑炎流行状况调查

目的调查云南省景东县流行性乙型脑炎的流行现状。方法媒介蚊虫调查采用诱蚊灯通宵捕蚊方法,蚊虫乙脑病毒检测采取RT-PCR方法,健康人群血清乙脑病毒抗体检测采用ELISA。结果共采集到蚊虫4属15种6653只,其中三带喙库蚊和中华按蚊属于当地的优势种群,分别占总捕获蚊数的82.07%和10.46%。RT-PCR检测三带喙库蚊和中华按蚊共16批1310只,各有1株感染乙脑病毒;ELISA检测当地健康人群血清乙脑病毒抗体阳性率为72.96%,不同年龄组人群乙脑病毒抗体水平差异有统计学意义(χ2=51.589,P0.01)。结论云南景东县蚊虫种类较多,三带喙库蚊和中华按蚊有传播乙型脑炎的作用。     

First isolation of Japanese encephalitis from Culex quinquefasciatus in Thailand

Isolation of Japanese encephalitis (JE) virus using C6/36 cell and immunofluorescence virus antigen detection techniques was attempted from female mosquitoes collected with CDC gravid traps in Samut Songkhram Province in the central region and in Phuket Province in southern Thailand, in 2003. One thousand and eighty female mosquitoes including 6 species of the Culicidae family (Culex quinquefasciatus, Cx. gelidus, Cx. tritaeniorhynchus, Cx. whitmorei, Cx. vishnui complex, Cx. s.g. culiciomyia) (pooled by specific specimen), were processed for virus isolation. Two pools of Cx. quinquefasciatus yielded a JE virus isolation. This represents the first report of JE virus isolation from Cx. quinquefasciatus in Thailand.     

Distribution of mosquitoes and mosquito-borne viruses along the China-Myanmar border in Yunnan Province

A total of 54,673 mosquitoes were collected at 11 sites located near the China-Myanmar border in the western part of Yunnan Province during July and August 2007. There were 29 species in 4 genera identified from the collections, including 12 species of Culex, 12 species of Anopheles, 3 species of Aedes, and 2 species of Armigeres. Culex tritaeniorhynchus Giles (67.9%, 37,119/54,673) and Anopheles sinensis Wiedemann (25.9%, 14,170/54,673) were the most abundant species in this investigation. Virus was isolated using BHK-21 and C6/36 cells from 22 of 510 mosquito pools. Isolates included Japanese encephalitis virus (JEV) and Getah virus (GETV), which were identified by serological and molecular methods. Twenty JEV strains were isolated from Cx. tritaeniorhynchus (15 isolates), An. sinensis (3 isolates), and Armigeres subalbatus Coquillett (2 isolates), and 2 GETV strains were isolated from Culex pseudovishnui Colless and Cx. tritaeniorhynchus. This study suggests that Ar. subalbatus is a potentially important local vector because of the high JEV infection ratio found in this species. Enzootic JEV transmission persists in this area and therefore, surveillance for human disease caused by JEV and GETV should be conducted in the region.     

Outdoor resting preference of Culex tritaeniorhynchus, the vector of Japanese encephalitis in Warangal and Karim Nagar districts, Andhra Pradesh

BACKGROUND & OBJECTIVES: Entomological investigations were carried out in Warangal and Karim Nagar districts of Andhra Pradesh during viral encephalitis outbreak in July 2003. METHODS: Adult mosquito collections in outdoor were done using sweep cage method and in indoor with the help of aspirator tube and flash light. Larval collections were done by dipping method. JE virus positivity was tested by IgM capture ELISA test. RESULTS: Outdoor collections revealed presence of Culex tritaeniorhynchus, Cx. bitaeniorhynchus and Cx. gelidus and in indoor collections--Cx. quinquefasciatus, Cx. tritaeniorhynchus, An. vagus and An. subpictus. In the outdoor collections Cx. tritaeniorhynchus was predominant (96.3% of total collection). Three samples out of 55 serum samples from human cases and five from contacts showed the presence of antibodies against JE virus. INTERPRETATION & CONCLUSION: Cx. tritaeniorhynchus, a known vector of JE is predominant in outdoors and playing a main role in JE transmission in this area. Vector control aimed at the outdoor resting population might limit virus circulation in the mosquito vertebrate host cycle and prevent human infection.     

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。     

中国云南湄公河上游乙型脑炎传播媒介生物学及行为的研究

目的　探讨乙型脑炎病毒媒介在人房的季节消长、嗜血习性和叮人行为,以及其幼虫相关的生物学习性, 从而制定出有效的媒介控制措施。　方法　2001 年 6~12 月,在云南南部湄公河上游,选取一个种植场,采用 CDC 诱蚊灯和人工诱捕的方法捕蚊;蚊胃血源环状沉淀法鉴定其嗜血习性以及孳生地调查幼虫孳生习性。　结果　共捕获乙脑病毒媒介蚊虫5属、11种、5 726只。无论是诱蚊灯还是人工诱蚊法,三带喙库蚊、伪杂鳞库蚊、棕头库蚊和中华按蚊的季节密度高峰都出现于 6~8 月的雨季;3 种库蚊在村内和村外有整夜叮咬活动,但中华按蚊的叮人高峰出现在 21:00 之前。人房室内诱蚊灯捕蚊与室外人诱观察发现,室内捕捉乙脑病媒数量远高于室外。蚊胃血检测结果发现它们的人血指数都比较高;幼虫具有明显的特征性分布。　结论　湄公河上游地区人房优势蚊种三带喙库蚊、伪杂鳞库蚊、棕头库蚊和中华按蚊的生物学及行为与以往畜圈调查的结果存在着差异。     

Growth characteristics of the chimeric Japanese encephalitis virus vaccine candidate, ChimeriVax-JE (YF/JE SA14--14--2), in Culex tritaeniorhynchus, Aedes albopictus, and Aedes aegypti mosquitoes

The Japanese encephalitis (JE) virus vaccine candidate, ChimeriVax-JE, which consists of a yellow fever (YF) 17D virus backbone containing the prM and E genes from the JE vaccine strain JE SA14--14--2, exhibits restricted replication in non-human primates, producing only a low-level viremia following peripheral inoculation. Although this reduces the likelihood that hematophagous insects could become infected by feeding on a vaccinated host, it is prudent to investigate the replication kinetics of the vaccine virus in mosquito species that are known to vector the viruses from which the chimera is derived. In this study ChimeriVax-JE virus was compared to its parent viruses, as well as to wild-type JE virus, for its ability to replicate in Culex tritaeniorhynchus, Aedes albopictus, and Aedes aegypti mosquitoes. Individual mosquitoes were exposed to the viruses by oral ingestion of a virus-laden blood meal or by intrathoracic (IT) virus inoculation. ChimeriVax-JE virus did not replicate following ingestion by any of the three mosquito species. Additionally, replication was not detected after IT inoculation of ChimeriVax-JE in the primary JE virus vector, Cx. tritaeniorhynchus. ChimeriVax-JE exhibited moderate growth following IT inoculation into Ae. aegypti and Ae. albopictus, reaching titers of 3.6-5.0 log(10) PFU/mosquito. There was no change in the virus genotype associated with replication in mosquitoes. Similar results were observed in mosquitoes of all three species that were IT inoculated or had orally ingested the YF 17D vaccine virus. In contrast, all mosquitoes either IT inoculated with or orally fed wild-type and vaccine JE viruses became infected, reaching maximum titers of 5.4-7.3 log(10) PFU/mosquito. These results indicate that ChimeriVax-JE virus is restricted in its ability to infect and replicate in these mosquito vectors. The low viremia caused by ChimeriVax-JE in primates and poor infectivity for mosquitoes are safeguards against secondary spread of the vaccine virus.     

云南省景洪市虫媒病毒调查分析

近１０多年来，先后从云南省景洪市各乡镇的当地病人、猪、蝙蝠和蚊虫体内分离出乙型脑炎病毒２２株，从白纹伊蚊中分离到登革４型病毒１株，从蝙蝠和蚊体内分离到基孔肯雅病毒５株，从患急性期血液中分离到辛德毕斯病毒１株，从发热病人血液、脑炎病人脑脊液、猪血清和牛血清中分离到新环状病毒４７株，从黄胸鼠肺脏中检查出流行性出血热病毒抗原阳性６份；人群、猪恒河猴或鼠类血清中亦检出上述６种病毒的抗体，表明景洪市存在乙     

Proposal for Japanese encephalitis surveillance using captured invasive mongooses under an eradication project on Okinawa Island, Japan

A project to eradicate invasive small Asian mongooses (Herpestes javanicus) is underway to conserve the unique ecosystem of Okinawa Island, Japan. In the present study, we tried to elucidate whether the mongoose is a host of Japanese encephalitis virus (JEV) and to evaluate the reliability of surveillance of Japanese encephalitis (JE) using this species. Culex tritaeniorhynchus, the main vector mosquito of JEV, feeds on the mongoose. Eighty-five (35.4%) of 240 wild small Asian mongooses captured between 2001 and 2005 had neutralizing antibodies against more than one of four JEV strains. Prevalence rates of JEV antibodies tended to increase with body weight and length of the animals. One of three sentinel mongooses showed a temporal change in antibody titer. These results indicate that the small Asian mongooses on Okinawa Island are sensitive to JEV. From the antibody titers and the locations of capture, the JEV active area was clarified. We propose that surveillance of JE using mongooses captured under the eradication program is reliable.     

Vectors of Japanese encephalitis virus (JEV): species complexes of the vectors

The vectors of JEV are Cx. tritaeniorhynchus, Cx. vishnui, Cx. pseudovishnui, Cx. gelidus, Cx. fuscocephala, Cx. quinquefasciatus, Cx. pipiens pallens, Cx. bitaeniorhynchus, Cx. annulirostris, Aedes togoi, Ae. japonicus, Ae. vexans nipponii, Anopheles annularis and An. vagus. Cx. tritaeniorhynchus is in the tritaeniorhynchus complex, breeds in rice fields, ground pools in vast areas. Two types of mating behavior, eurygamy and moderate stenogamy were detected. In the case of the eurygamy type, the mosquitoes were from Southern Thailand and hilly areas near Kanchanaburi, Thailand. Female mosquitoes are usually dark in color, the cibarial armature has rod teeth and the posterior end of the cibarial armature is bowl shaped with a typical rim. The rim of the bowl is everted. The moderate stenogamy type were mosquitoes from the plain areas such as Bangkok, Ayutthaya, Suphan Buri and Saraburi. The posterior end of the cibarial armature is bowl shaped with a stout rim. The larvae were characteristic in their siphon index, antennal index, hair O of prothoracic segment, and comb scale number and arrangement. Cx. tritaeniorhynchus summorosus from Japan, Los Banos and Luzon, Philippines, differed from Cx. tritaeniorhynchus in that on the lateral plate of the phallosome tritaeniorhynchus teeth are somewhat weakly developed and only gently curved whereas in tritaeniorhynchus summorosus they are strongly developed, considerably longer, and sharply recurved. The siphons of larvae are short, the sides parallel and the apex truncate in tritaeniorhynchus whereas in tritaeniorhynchus summorosus they are long and slender. Cx. tritaeniorhynchus var. siamensis is possibly present. Colonies have been maintained in the Department of Medical Entomology for 31 generations. The characteristics are in hair O (short, less than 20 branches, and without secondary branching and the larval siphon (short and broad where the others are long). Cx. vishnui and Cx. pseudovishnui are in the vishnui complex. Cx. quinquefasciatus and Cx. pipiens pallens are in the Cx. pipiens complex comprising: (1) Cx. pipiens; (2) Cx. quinquefasciatus Say; (3) Cx. molestus Forskal; (4) Cx. pipiens pallens; (5) Cx. australicus; (6) Cx. globocoxitus. Anopheles annularis is a species complex evidenced by two types of polytene chromosomes.     

云南省德宏州蚊虫分布特点及乙型脑炎病毒分离

１９８３年５月以及１９８４年和１９８９年７￣８月，在云南省德宠州路西，瑞丽和盈江三县，市捕获成年雌性蚊虫９属４４种１９０８３只。三带喙库蚊，霜背库蚊，棕头库蚊和中华按蚊是农村畜圈的主要蚊种。伪白纹伊蚊和白纹伊蚊是野外竹林区的优势蚊种。对所获蚊虫用Ｃ６／３６细胞和乳鼠方法分离病毒，结果从三带喙库蚊中分离到乙型脑炎病毒２株，从霜背库蚊，白纹伊蚊和窄翅伊蚊中各分离出１株乙型脑炎病毒。分析认为，三带喙库蚊     

Mosquito blood feeding patterns as a factor in the epidemiology of Japanese encephalitis in southern India.

Determinations were made of the source of 16,330 bloodmeals from 10 species of Culex mosquitoes, including recognized vectors of Japanese encephalitis (JE) virus, in two epidemiologically distinct areas in southern India. In Madurai, where cases occurred sporadically and pigs were reared only in some villages, Cx. tritaeniorhynchus, Cx. pseudovishnui, and Cx. vishnui had fed predominantly on cattle (89.2-91%), but less frequently on humans (2.1-6.2%) and on pigs and ardeid birds (0-0.1%). In Nallur, which was endemic for JE and had a large pig population, 4.4-5.4% of the feedings were on these hosts. Cattle feedings accounted for 84.6-88% of the total feedings, human feedings for 2.4-6.2%, but there were no ardeid-positive feedings. Culex tritaeniorhynchus and Cx. vishnui showed a marked increase in the proportion of human feedings during the hot season, due to increased availability of humans sleeping outdoors to mainly exophagic mosquitoes. Feeding indices were corrected for spatial and temporal concurrence of hosts in each season, but these factors were found to require further elucidation. Discrepancies in the relative abundance of vectors as monitored by two different methods are discussed in the light of these observations.     

Influence of the distribution of host species on adult abundance of Japanese encephalitis vectors Culex vishnui subgroup and Culex gelidus in a rice-cultivating village in northern Vietnam

A field study was conducted in a village in northern Vietnam to investigate how host distribution influences Japanese encephalitis (JE) vector abundance. Indoor and outdoor collections were conducted from 50 compounds. We collected three JE vector species--Culex tritaeniorhynchus and Culex vishnui that comprised the Culex vishnui group, and Culex gelidus. Spatial autocorrelation was not observed in the mosquito assemblies at any scale larger than the house compounds. Multivariate analyses revealed that the Cx. gelidus density correlated positively with both the host proximity to the breeding sites and cattle density; however, the Cx. vishnui subgroup density correlated positively only with cattle density. These results showed that the number of cattle in a compound influenced the JE vector abundance in that compound, and the abundance of Cx. gelidus, not of the Cx. vishnui subgroup, was affected by the host proximity to the breeding sites in the village.     

First time detection of Japanese encephalitis virus antigen in dry and unpreserved mosquito Culex tritaeniorhynchus Giles, 1901, from Karnal district of Haryana state of India

Japanese encephalitis virus (JEV) antigen has been detected by antigen capture enzyme linked immunosorbentassay (ELISA) in dry specimens of the mosquito Culex tritaeniorhynchus Giles, 1901, collected from Karnal district of Haryana state in northern India. These mosquitoes were stored in dry condition for 20 months, at room temperature, before processing. The procedure of detecting JEV infection in long time stored, dry vector mosquitoes, has important application in the surveillance of Japanese encephalitis.     

云南省西双版纳州蚊虫分布特点及与虫媒病毒的关系

１９８１、１９８２、１９８３、１９８６、１９８７和１９８８年在西双版纳州景洪、勐海和勐腊县（市）捕获成年雌性蚊虫８属３４种３４５０８只。夜晚在农村畜圈及其周围采获蚊虫２１种,优势蚊种为棕头库蚊和三带喙库蚊;白天在野外竹林采获蚊虫２５种,优势蚊种为贺斑伊蚊和白蚊伊蚊。从三带喙库蚊（８株）、霜背库蚊（４株）、伪杂鳞库蚊（３株）、环带库蚊（１株）、棕头库蚊（１株）、中华按蚊（３株）、刺扰伊蚊（２株）、白