Effects of temperature on virogenesis of bluetongue virus serotype 11 in Culicoides variipennis sonorensis

Abstract. Culicoides variipennis sonorensis females were fed bluetongue virus serotype 11 mixed in sheep blood and were held at constant temperatures of 32, 27, 21 and 15^oC. Virogenesis, as measured by enzyme-linked immunosorbent assay (ELISA), proceeded significantly faster at higher temperatures. Based on ELISA absorbance ≥0.2, some flies first were categorized as infected after 1 day, 2 days and 4 days at 32, 27 and 21^oC, respectively. Peak levels of virus antigen were seen after 5–7, 7–13 and 18–22 days for flies held at 32, 27 and 21^oC, respectively. There was no significant virus replication in flies held at 15^oC for 22 days, but latent virus replicated and was detected easily (44% infection) 4–10 days after these flies were transferred to 27^oC. The implications for temperature effects on bluetongue epizootiology are discussed.     

Exposure to chikungunya virus and adult longevity in Aedes aegypti (L.) and Aedes albopictus (Skuse)

Chikungunya virus (CHIKV) recently emerged as a global threat to public health through its adaptation to the cosmopolitan mosquito Aedes albopictus Skuse. Aedes albopictus is highly susceptible to the emergent strain of CHIKV, relative to the historical vector of CHIKV, Aedes aegypti (L.). We hypothesized that the high susceptibility of Ae. albopictus to CHIKV may have a cost in terms of longevity and fecundity among infected vs non‐infected mosquitoes, relative to Ae. aegypti. We performed a longevity experiment comparing Ae. aegypti and Ae. albopictus exposed to the emergent strain of CHIKV (LR‐2006OPY1). We found a small but significant decrease in longevity of Ae. albopictus, but not Ae. aegypti, in response to exposure to CHIKV. We did not observe significant differences in numbers of eggs laid by either species in response to exposure. Longevity and body titer of infected Ae. albopictus were significantly negatively correlated, such that individuals that lived longer had lower viral body titers when they died. The cost of exposure, while not high, suggests there may be physiological constraints in the evolution of viral infectiousness in its insect vector.     

Mosquito‐borne West Nile virus (WNV) surveillance in the Upper Rhine Valley,Germany

West Nile virus (WNV) could be introduced into Germany via migratory birds originating from Africa or southern Europe and subsequently transmitted to indigenous birds, humans, or horses by mosquitoes. Neither the virus itself nor antibodies against WNV have yet to be found in mosquitoes and horses, whereas antibodies have been detected in migrating birds and in humans that were in close contact with birds. At present, the West Nile virus itself has yet to be detected in Germany. This investigation was conducted primarily in major bird breeding, resting, and roosting habitats (hotspots) in the Upper Rhine Valley. Adult mosquitoes were trapped using CO₂‐baited Encephalitis Vector Surveillance (EVS)‐traps and were tested for WNV by the VecTest WNV Antigen Assay. In 2007 and 2008, a total of 11,073 host‐seeking adult female mosquitoes (13 species) were tested, and all tests were negative for WNV. Statistical calculations could be performed only where sufficient numbers of mosquitoes were trapped. For these sites, WNV infection among mosquitoes could be ruled out with 80% certainty. For the evaluation of the WNV situation in Germany, the results of this investigation are a further indication that the virus has not yet arrived.     

First report of the oriental mosquito Aedes albopictus on the West African island of Bioko,Equatorial Guinea

The invasive oriental mosquito Aedes (Stegomyia) albopictus (Skuse) (Diptera: Culicidae) was detected on Bioko Island for the first time in November 2001. It was found to be well established breeding in artificial containers at Planta, near Malabo, the capital of Equatorial Guinea. Associated species of mosquito larvae were Aedes aegypti (L.), Ae. africanus (Theobald), Culex near decens Theobald, Cx. duttoni Theobald, Cx. quinquefasciatus Say, Cx. tigripes De Grandpré & De Charmoy, Eretmapodites quinquevittatus Theobald and Mansonia africana (Theobald). This is the third tropical African country to be invaded by Ae. albopictus, which has recently spread to many parts of the Americas and Europe--with vector competence for dengue, yellow fever and other arboviruses. In the Afrotropical environment, it will be interesting to monitor the ecological balance and/or displacement between introduced Ae. albopictus and indigenous Ae. aegpyti (domestic, peri-domestic and sylvatic populations).     

Antigenic relationships between adult and larval Anopheles tessellatus midgut glycoproteins and the midguts of other vector mosquitoes

Glycoproteins expressed on the surface of midgut (MG) epithelium and the peritrophic matrix (PM) of vector mosquitoes (Diptera: Culicidae) are candidate molecules for interacting with pathogens. Antisera produced against Anopheles tessellatus Theobald female MG lectin-binding proteins (concanavalin A and wheat germ agglutinin) were used in Western blots to investigate MG/PM antigenic relationships between adult and larval An. tessellatus and with the MG glycoproteins of other vector mosquitoes: Anopheles culicifacies Giles, An. subpictus Grassi, An. varuna Iyengar, Aedes aegypti (L.) and Culex quinquefasciatus Say. Within An. tessellatus, strong antigenic cross-reactions were observed between adult and larval MG proteins, and between adult MG and PM proteins. Anopheles tessellatus adult MG antisera reacted with MG antigens from adult females of the other five mosquito species, with interspecific contrasts of relative molecular mass (Mr) of nearly all reacting antigens, except the strong 36 kDa band shared by An. tessellatus and Cx. quinquefasciatus. Cross-reactivity within female An. tessellatus may be due to the MG containing precursors to the PM glycoproteins and/or some common fully processed proteins, or perhaps carbohydrate epitopes that are shared between related or unrelated MG and PM glycoproteins. Cross-reactions between adult MG proteins from different mosquito species, mostly with differential Mr, reflect the presence of homologous proteins that may be relevant to specific vector competence.     

Quantitative Risk Assessment of the Pathways by Which West Nile Virus Could Reach Hawaii

The introduction of West Nile virus (WNV) to Hawaii could have severe impacts on human health, wildlife health and, as a result, Hawaiis tourism-based economy. To provide guidance for management agencies seeking to prevent the introduction of WNV, we performed a quantitative assessment of the pathways by which WNV could reach Hawaii from North America. We estimated the rate of infectious individuals reaching Hawaii by the following means (1) humans on aircraft, (2) wind-transported mosquitoes, (3) human-transported mosquitoes, (4) human-transported birds or other vertebrates, and (5) migratory birds. We found that pathways 3 and 4 represented the highest risk. We estimated that each year, 7–70 WNV infectious mosquitoes will reach Hawaii by airplane when WNV becomes well established in the Western U.S. Exemptions in current quarantine regulations will also result in the import of birds that will be infectious with WNV for 0.3–2.2 bird-days each year. We propose actions that would substantially reduce the risk of WNV reaching Hawaii by these means, including reinstating aircraft disinsection in cargo holds and altering bird quarantine rules. Finally, research is urgently needed to determine whether a migratory bird can survive the migration from North America to Hawaii with a viremic WNV infection.     

Dicer-2-Dependent Generation of Viral DNA from Defective Genomes of RNA Viruses Modulates Antiviral Immunity in Insects

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Analysis of trapped mosquito excreta as a noninvasive method to reveal biodiversity and arbovirus circulation

Emerging and endemic mosquito-borne viruses can be difficult to detect and monitor because they often cause asymptomatic infections in human or vertebrate animals or cause nonspecific febrile illness with a short recovery waiting period. Some of these pathogens circulate into complex cryptic cycles involving several animal species as reservoir or amplifying hosts. Detection of cases in vertebrate hosts can be complemented by entomological surveillance, but this method is not adapted to low infection rates in mosquito populations that typically occur in low or nonendemic areas. We identified West Nile virus circulation in Camargue, a wetland area in South of France, using a cost-effective xenomonitoring method based on the molecular detection of virus in excreta from trapped mosquitoes. We also succeeded at identifying the mosquito species community on several sampling sites, together with the vertebrate hosts on which they fed prior to being captured using amplicon-based metabarcoding on mosquito excreta without processing any mosquitoes. Mosquito excreta-based virus surveillance can complement standard surveillance methods because it is cost-effective and does not require personnel with a strong background in entomology. This strategy can also be used to noninvasively explore the ecological network underlying arbovirus circulation.     

2014年甘肃省部分地区蚊虫及蚊媒病毒调查

为调查甘肃省部分地区蚊虫及蚊媒病毒的种类及分布,本课题组2014年在甘肃省酒泉市和陇南市地区共采集蚊虫4 412只.酒泉市共采集蚊虫2属3种2 833只,其中背点伊蚊(Aedes dorsalis)2 665只(94.1％)、刺扰伊蚊(Aedes vexans)150只(5.3％)、淡色库蚊(Culex pipiens pallens)18只(0.6％);陇南市共采集2属2种1 579只蚊虫,其中淡色库蚊1 451只(91.9％)、中华按蚊(Anopheles sinensis)128只(8.1％).经实验室常规处理后,将蚊虫标本分为96批,接种于C6/36、BHK和Vero细胞,进行病毒分离和多种病毒基因特异性扩增检测.结果显示,96批蚊虫标本在3种细胞中均未出现细胞病变效应(cytopathic effect,CPE),在18批蚊虫标本研磨液中检测到辽宁病毒(Liaoning virus,LNV)基因阳性.病毒核苷酸序列的遗传进化分析显示,在甘肃省检测到的辽宁病毒与此前在我国新疆维吾尔自治区发现的辽宁病毒亲缘关系最近.