三带喙库蚊胸腔接种乙型脑炎减毒活疫苗病毒的感染动态及致病力观察

目的通过蚊虫胸腔接种乙脑病毒减毒活疫苗SA14-14-2株,了解该疫苗病毒在蚊虫体内的繁殖情况及其毒力稳定性,进一步评价该疫苗的安全性。方法建立三带喙库蚊的实验室种群,用SA14-14-2、SA14和中山株胸腔接种三带喙库蚊,感染后不同时间取一定数量的蚊虫,研磨制成悬液,用空斑试验检测蚊虫体内的病毒滴度。用感染蚊悬液接种乳鼠和感染蚊虫直接叮咬乳鼠的方法,观察对乳鼠的致病性。结果SA14-14-2、SA14和中山株病毒感染蚊虫后,第2~20d蚊虫体内均能检测到病毒,其中SA14-14-2株的滴度为2~3.72 logPFU/ml,SA14株为3~4.85 logPFU/ml,中山株为3~5.40 log-PFU/ml。中山株的感染滴度最高,其次是SA14株,SA14-14-2株的感染滴度最低,表明蚊虫对野毒株(中山株和SA14株)更为敏感。感染SA14-14-2病毒的三带喙库蚊悬液接种乳鼠,未能引起乳鼠发病或死亡。感染SA14-14-2病毒的三带喙库蚊叮咬乳鼠,未见乳鼠发病或死亡,也未从小白鼠血清中检测到乙脑病毒抗体。结论经胸腔接种,SA14-14-2病毒能在三带喙库蚊体内稳定繁殖。动物接种和蚊虫叮咬试验表明,经蚊体内繁殖的SA14-14-2病毒毒力仍保持原有的弱毒特性,表明该减毒活疫苗通过蚊虫体内繁殖后不会造成传播。     

乙脑病毒经三带喙库蚊卵传递的实验研究

本文用乙脑病毒-蔗糖-人红细胞混合物摄食法感染雌性三带喙库蚊,共感染18组(1166只),其中13组感染成功,并从2组子代蚊检出乙脑病毒。传递到子代蚊的乙脑病毒仍保持毒力。     

乙型脑炎病毒SA14-14-2株E基因的克隆、测序与表达

目的　克隆乙型脑炎病毒E基因并在大肠杆菌中进行表达 ,为今后研制乙脑分子诊断试剂盒和基因工程疫苗奠定基础。方法　根据乙型脑炎病毒株SA14 - 14 - 2E基因的序列设计一对引物 ,采用RT -PCR技术扩增其E基因全长cD NA ,将扩增产物克隆到pBlusecriptIISK(+)载体中 ,然后亚克隆到原核表达载体PGEX -KG中 ,筛选重组质粒 ,转化大肠杆菌BL2 1(DE3)表达重组蛋白。结果与结论　获得了含全长乙型脑炎病毒E基因的重组质粒 ,经酶切和测序证实构建正确。表达的目的蛋白经SDS -PAGE和Westernblot分析证实确为乙型脑炎病毒E蛋白且有生物学活性。     

Characteristics of Chimeric West Nile Virus Based on the Japanese Encephalitis Virus SA14-14-2 Backbone

West Nile virus disease (WND) is an arthropod-borne zoonosis responsible for nonspecific fever or severe encephalitis. The pathogen is West Nile virus belonging to the genus Flavivirus, family Flaviviridae. Every year, thousands of cases were reported, which poses significant public health risk. Here, we constructed a West Nile virus chimera, ChiVax-WN01, by replacing the prMΔE gene of JEV SA14-14-2 with that of the West Nile virus NY99. The ChiVax-WN01 chimera showed clear, different characters compared with that of JEV SA14-14-2 and WNV NY99 strain. An animal study indicated that the ChiVax-WN01 chimera presented moderate safety and immunogenicity for 4-week female BALB/c mice.     

流行性乙型脑炎病毒SA14-14-2株E蛋白基因在原核细胞中的高效表达及其表达产物的抗原性分析

目的　获得JEVE蛋白基因并使其在E coli中高效表达 ,以研究其抗原活性 ,为进一步研制ELISA早期诊断试剂盒奠定基础。方法　根据已发表的JEVSA - 14 - 14 - 2减毒株序列 ,设计一对特异性引物 ,通过RT -PCR扩增出E蛋白基因的cDNA片段 ,并将其克隆入 pET - 32a(+)表达载体中 ,构建重组融合表达载体pET -E ,转化大肠杆菌BL2 1(DE3)后 ,利用IPTG诱导获得高效表达。结果　扩增的E蛋白基因片段长 1113bp ,编码 371个氨基酸残基 ,该基因片段与国内发表的减毒株SA14 - 14 - 2碱基序列同源性为 10 0 %。表达产物分子量约为 6 2kD ,经Westernblotting分析表明表达产物具有较好的抗原性。结论　通过序列分析表明 ,我国的JEVSA - 14 - 14 - 2减毒株未发生基因突变。表达产物的稳定高效表达及其抗原特异性分析为今后ELISA早期诊断试剂盒的研制提供了依据。     

Longitudinal studies in South Indian villages on Japanese encephalitis virus infection in mosquitoes and seroconversion in goats

Japanese encephalitis (JE) is endemic in Cuddalore district, Tamil Nadu, where Culex tritaeniorhynchus Giles was the major vector. We screened 45 100 adult female Cx. tritaeniorhynchus (902 pools) by enzyme-linked immunosorbent assay and isolated and confirmed JE virus (JEV) by using an insect bioassay system. We had 69 isolates of which 62 (90%) were identified as JEV. The average vector abundance per man hour for Cx. tritaeniorhynchus was 324.5 per month for the period June 1998-May 2000. The average minimum infection rate (MIR) per month in Cx. tritaeniorhynchus was 1.4 (range 0.0-5.6). Every year, a new batch of goats, 20 in the first year and 31 in the second year, born during the non-JE transmission period (January-June), aged <6 months and negative for haemagglutination inhibition (HI) antibodies were procured and placed in the villages as sentinels. Fortnightly, blood specimens were collected from these goats and tested for JE antibodies by HI test. Seroconversions (SCs) were recorded in 14 goats (70%) in the first year and 23 goats (74%) in the second year. JE HI antibody titres in goats were low (1:10-1:80) and these levels declined to undetectable levels in about 4 weeks following SCs. The time sequence of events indicated that four of five peaks of MIR in mosquitoes were followed 1-3 months later by peaks in the proportion of seroconverted goats. We suggest the screening of goats and cattle as a more feasible tool to stratify areas according to JE infection risk to the human population through the regular health system rather than screening mosquitoes using monoclonal antibodies, which is possible only in specialized laboratories.     

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.