Isolation of Japanese encephalitis virus from mosquitoes collected in Karnataka state, India from 1985 to 1987

Detection and isolation of Japanese encephalitis (JE) virus using mosquito inoculation and immunofluorescence techniques were attempted from female mosquitoes collected in JE endemic areas of Kolar and Mandya districts of Karnataka state, India, from 1985 to 1987. 65,388 mosquitoes consisting of 19 species in 1541 pools were processed. Of these, 18 pools showed the presence of JE virus antigen. JE virus was isolated from 9 pools, 3 of Culex gelidus, 2 of C. tritaeniorhynchus, and one each of C. quinquefasciatus, C. fuscocephala, C. vishnui and Anopheles peditaeniatus. Isolation of JE virus from C. gelidus, C. fuscocephala, C. quinquefasciatus and An. peditaeniatus is reported for the first time in India.     

Flavivirus isolations from mosquitoes collected from western Cape York Peninsula, Australia, 1999-2000

After the 1st appearance of Japanese encephalitis virus (JE) on mainland Australia in 1998, a study was undertaken to investigate whether JE had become established in enzootic transmission cycles on western Cape York Peninsula. Adult mosquitoes were collected during the late wet season from Kowanyama and Pormpuraaw in April 1999, and Pormpuraaw and Barr's Yard in April 2000. Despite processing 269,270 mosquitoes for virus isolation, no isolates of JE were obtained. However, other flaviviruses comprising Murray Valley encephalitis virus, Kunjin virus, Alfuy virus, and Kokobera virus (KOK) were isolated. Isolates of the alphaviruses Ross River virus, Barmah Forest virus (BF), and Sindbis virus (SIN) also were obtained. The majority (88%) of isolates were from members of the Culex sitiens subgroup. Single isolates of KOK, BF, and SIN were obtained from Ochlerotatus vigilax, Oc. normanensis, and Anopheles bancroftii, respectively. The isolations of flaviviruses during the late wet season indicate that conditions were suitable for flavivirus activity in the area. No evidence was found to suggest that JE has become established in enzootic transmission cycles on western Cape York, although study sites and field trips were limited.     

Heterogeneity in the host preference of Japanese encephalitis vectors in Chiang Mai, northern Thailand

Experiments, using the capture-mark-release-recapture technique inside large nets, were carried out in Chiang Mai, northern Thailand, to examine heterogeneity in the host preference of Japanese encephalitis (JE) vectors. A significantly higher proportion of the vector species that were initially attracted to a cow fed when released into a net with a cow than when released into a net containing a pig. However, Culex vishnui individuals that had been attracted to a pig had a higher feeding rate in a net containing a pig rather than a cow. When mosquitoes were given a choice by being released into a net containing both animals, they exhibited a tendency to feed on the host to which they had originally been attracted. This feeding preference was, however, not shown by the offspring of pig-fed individuals. We have therefore shown evidence of physiological/behavioural conditioning in the host preference of JE vectors rather than genetic variability. Our results suggest that effective control of JE might be achieved by increasing the availability of cows (the dead-end hosts of JE virus) to deflect the vectors from pigs (the amplifying host). The behavioural imprinting which we have found would tend to re-inforce the initial tendency of the vectors to bite cows.     

Bunyavirus isolations from mosquitoes in the western Canadian Arctic.

Strains of California encephalitis virus (snowshoe hare subtype) were isolated from 8 of 475 pools comprising 23 747 unengorged female mosquitoes of five species collected at three of six locations throughout the Mackenzie Valley of the Northwest Territories, Canada, from latitudes 60 to 69 degrees N between 10 and 24 July 1976. Minimum field infection rates included 1:2734 for Aedes communis, 1:256 to 1:3662 for A. hexodontus and 1:911 to 1:1611 for A. punctor. Northway virus was also isolated from 1 of 3662 A. hexodontus mosquitoes collected at Inuvik (69 degrees N, 135 degrees W). Transmission of CE virus by A. communis infected by feeding on virus in defibrinated blood and incubation at 0, 13 and 23 degrees C for 13-20 days clearly demonstrates the importance of this species as a natural vector, and transmission of CE virus by Culiseta inornata after incubation at 0 and 13 degrees C following intrathoracic injection strengthens evidence of its role as a natural vector. Immunofluorescence was less reliable than imunoperoxidase for detection of CE viral antigen in mosquito salivary glands.     

Japanese encephalitis virus from pigs and mosquitoes in Jakarta, Indonesia.

Japanese encephalitis virus was isolated from 11 pools of Culex tritaeniorhynchus and a single pool of C. gelidus mosquitoes at a pig-raising area near Jakarta, West Java, Indonesia, during 1972-74. Ten sentinel pigs placed in the area all developed haemagglutination-inhibition antibodies against Japanese encephalitis and the virus was isolated from the blood of 3.     

浙江省蚊虫中乙型脑炎病毒的分离及鉴定

目的 对2007年浙江省采集的蚊虫标本进行病毒分离与鉴定.方法 2007年在浙江省采集蚊虫标本,用金黄地鼠肾细胞(BHK-21)分离病毒,对新分离的病毒进行血清学和分子生物学鉴定.结果 采集到4735只蚊虫,分离到2株致BHK-21细胞病变的病毒,经免疫荧光和RT-PCR试验鉴定为乙型脑炎病毒(JEV),利用病毒PrM区段进行基因分型分析,新分离的2株病毒属于基因Ⅰ型JEV.对这2株病毒的E基因区段进行分析,核苷酸和氨基酸的同源性分别为99.0%和98.8%.与疫苗株SA14-14-2相比,核苷酸同源性在87.7%,氨基酸同源性在96.4%以上,共有14个共同的氨基酸位点差异.结论 在浙江省采集的蚊虫标本中分离到2株病毒,经鉴定为基因Ⅰ型JEV,是浙江省近年来首次分离.     

Change in Japanese encephalitis virus distribution, Thailand

Japanese encephalitis virus (JEV) genotypes in Thailand were studied in pigs and mosquitoes collected near houses of confirmed human JEV cases in 2003-2005. Twelve JEV strains isolated belonged to genotype I, which shows a switch from genotype III incidence that started during the 1980s.     

The pathogenesis of Japanese encephalitis virus in Culex tritaeniorhynchus mosquitoes

Culex tritaeniorhynchus were inoculated intrathoracically with mosquito and human strains of Japanese encephalitis virus and maintained at 26 degrees C or 32 degrees C. Virus titration and localization of viral antigen by avidin-biotin immunoperoxidase staining were done at intervals up to 21 days. Marked differences were noted in the tempo of organ involvement at the 2 temperatures; at both there was initial infection of fat body cells followed by selective infection of the central nervous system (CNS), with consistent infection of cells of the compound eye, patchy involvement of cephalic, thoracic and abdominal ganglia and no infection of Johnston's organ. CNS infection was always present 4 days after infection, when salivary gland involvement was first seen at 32 degrees C; at 26 degrees C CNS infection preceded salivary gland infection by 2 weeks. Late involvement of gut cells, pericardial cells and oviducts was also found, with no involvement of muscle.     

实时荧光RT—PCR快速检测蚊体内乙型脑炎病毒及福建省基因Ⅰ型乙型脑炎病毒的发现

目的:应用实时荧光RT-PCR方法快速检测蚊体内乙型脑炎病毒,并对蚊体内携带的乙型脑炎病毒进行基因分型。方法:从蚊媒监测点采集蚊标本,研磨后提取RNA,用新型的LNA探针实时荧光RT-PCR方法进行高通量快速筛查蚊体携带的乙型脑炎病毒,对核酸阳性的标本进一步用乙型脑炎病毒E基因特异引物进行RT-PCR扩增和序列测定,根据所测序列与GenBank中不同地理来源乙型脑炎病毒株E基因核苷酸序列分析的结果进行基因型别的判定。结果:12575只蚊子分成254份,用实时荧光RT-PCR方法从来源于福州的2份三带喙库蚊标本中检出乙型脑炎病毒核酸阳性,经RT-PCR及核苷酸序列测定,得到一段长1500nt的E基因核苷酸序列,序列分析结果显示,其核苷酸同源性最大的是来源于上海(DQ404100)和浙江(EU258742)的毒株,分别是99.1%和99.0%,均属于基因Ⅰ型病毒。结论:实时荧光RT-PCR方法是快速检测蚊体内乙型脑炎病毒的理想方法,此次调查发现的乙型脑炎病毒是以往福建省内未见报道的基因Ⅰ型病毒。     

Analysis of Japanese encephalitis epidemic in Western Nepal in 1997

We conducted an epidemiological study of a Japanese encephalitis (JE) outbreak in the southwestern part of Nepal in 1997. A high density of JE infections was found and it was estimated that 27.9% the total population were infected with JE virus in the study area. The fatality rate was 13.2% and there was no difference in the fatality rate between males and females over 5 years old. However, the case fatality rate was 2.1 times higher in females than in males (14.6% vs. 6.9%) among children under 5 years of age. Fifty-three blood samples were collected from suspected JE cases during the epidemic period in 1998. Findings for JE specific IgM revealed that clinical diagnoses of JE were serologically confirmed in an average 78% (70-93%) of patients in three collaborating hospitals. These studies demonstrated that JE was highly prevalent in the area and clinical diagnoses were reliable. Effective preventive measures should be taken against this vaccine-preventable disease.     

灵山县乙型脑炎媒介蚊虫的调查及控制方法

调查灵山县乙型脑炎流行村庄的人房、猪栏和牛舍,共捕获成蚊１３４３ 只,其中库蚊属２ 种、按蚊属２ 种、伊蚊属１ 种、阿蚊属１ 种,三带喙库蚊种群构成比占７５ ．３５ ％ 。同时调查乙脑病例村庄内及居民房外５００ｍ 以内的各种水体１３７ 处,蚊幼和蛹孳生地阳性率为４９ ．６ ％ 。蚊幼和蛹有５ 种,水体孳生阳性率三带喙库蚊最高,为３７ ．２ ％ ,其幼虫主要孳生地为稻田、莲藕田和田边沟渠。三带喙库蚊是灵山县的优势蚊种,也是这次乙脑流行的主要传播媒介。为控制乙脑疫情, 在人房和猪栏喷洒杀虫剂杀灭三带喙库蚊为防制的首选措施。     

Japanese encephalitis in a U.S. traveler returning from Thailand, 2004

Japanese encephalitis (JE) virus is a mosquito-borne flavivirus that is closely related to the West Nile and St. Louis encephalitis viruses endemic to North America. JE virus is a leading cause of viral encephalitis in Asia but is rarely reported among travelers to countries where JE is endemic. This report describes a case of an unvaccinated Washington resident who had JE after traveling to northern Thailand. The Advisory Committee on Immunization Practices (ACIP) recommends JE vaccine for travelers to JE-endemic areas of Asia during the transmission season, especially those spending > or =1 month in those areas and whose travel itineraries include rural settings. JE vaccine should also be considered for travelers visiting areas with epidemic transmission or those engaging in extensive outdoor activity in rural settings in areas where JE is endemic, regardless of the duration of their visit. In addition, health-care providers and organized international travel programs should ensure that travelers obtain appropriate preventive health guidance before travel.     

Antibodies to Japanese encephalitis virus in human sera collected from Irian Jaya. Follow-up of a previously reported case of Japanese encephalitis in that region

Japanese encephalitis virus (JEV) and other arboviruses are demonstrating an emergence in the southern part of New Guinea Island. JE was previously unknown in this part of the world until 1995 when it was found in the Torres Strait, northern Australia. In this study 96 sera collected from residents of the Timika region of Irian Jaya were tested for antibodies to JEV and related arboviruses by epitope-specific blocking ELISA. Of the 9 sera deemed to be positive for JEV antibodies by ELISA, 5 were collected from persons indigenous to Timika, and who had not travelled to regions where JE is known to be active. This indicates that these individuals were infected with JEV in the Timika area and supports a recent report of a clinical case of JE in this region. Non-immune expatriates visiting or working in the Lowland areas of Irian Jaya and/or Papua New Guinea should consider immunization against JE. Precautions should always be taken to avoid being bitten by any mosquito both in the daytime and at night.     

2005-2008年浙江省仙居县流行性乙型脑炎监测结果分析

目的了解流行性乙型脑炎（乙脑）流行规律,及时发现和控制疫情。方法按《全国流行性乙型脑炎监测方案》进行乙脑病例、疑似病例、宿主动物、蚊虫媒介及健康人群监测。结果仙居县2005-2008年监测疑似病例137例,实验室确诊乙脑10例,发病率为0.52/10万,无死亡病例;发病年龄均在7岁以下,发病时间集中在7月,有完整乙脑免疫史的1例;6月开始蚊密度进入高峰季节,三带喙库蚊是仙居县的主要蚊种之一,占捕获蚊虫总数的43.5%,2007年从捕获的蚊虫中分离到2株乙脑病毒,人群发病时间与蚊虫媒介密度升高相一致;宿主动物猪的乙脑总感染率为67.4%,猪乙脑感染率进入高峰季节比人群发病早1个月。结论仙居县广泛存在乙脑流行的自然因素,是乙脑的流行区,消灭乙脑免疫空白是防止和减少乙脑发生的最有效措施,开展乙脑监测能及时发现和控制疫情。