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Forest disturbance, mosquito vector ecology and La Crosse virus dynamics in southwestern VirginiaHarris, Maria-Richetta Camille 22 September 2014 (has links)
The influence of forest canopy disturbance (FCD) on La Crosse virus (LACV), leading cause of US pediatric arboviral encephalitis, is critical to understand in landscapes where forests are periodically harvested. Southwestern Virginia is part of an emerging focus of this interior forest bunyavirus. I investigated how the temperate forest mosquito community, LACV vectors, and the LACV amplifying vertebrate host (chipmunks) were impacted by logging. This research was conducted across an experimental FCD gradient (from least to most disturbed: contiguous control, fragmented control, clearcut, and high-leave shelterwood (SW)). Using gravid traps, I found that the mosquito community was resilient to logging with no significant difference in diversity or community composition across treatments. Mean number of female mosquitoes caught per trap-night declined with disturbance. FCD significantly affected the abundance of vector species in different ways. The primary LACV vector, Aedes triseriatus, and the recent invasive Ae. japonicus declined with logging. Other vectors (Ae. albopictus, Ae. canadensis, and Ae. vexans) thrived with logging. Culex pipiens/restuans was affected by disturbance but had no treatment preference. A mark-recapture study revealed that chipmunk abundance and LACV seroprevalence were greatest on the SW. In sync with Ae. triseriatus abundance but in contrast to the chipmunk results, mosquito LACV detection was significantly greater on unlogged sites. Surprisingly, LACV was detected in Ae. japonicus and Cx. pipiens/restuans. In a follow-up study, I isolated LACV from field-collected Ae. japonicus. Although LACV was previously isolated from Cx. pipiens, the vector competence was unknown. Therefore, I examined the vector competence of Cx. pipiens and Cx. restuans. Although poor vectors, I did detect LACV in the saliva of both species. An additional experiment found that nutritionally-stressed Cx. restuans were better vectors than those in the control group, indicating that environmental stressors (e.g., FCD) may alter the ability of accessory vectors to spread LACV. The influence of FCD on LACV is complex. Because logging decreases Ae. triseriatus abundance, human LACV risk is likely lowered by decreased transovarial vertical transmission. However, high chipmunk seroprevalence on disturbed sites suggest horizontal transmission with accessory vectors plays a larger role in LACV risk on recently logged sites. / Ph. D.
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Factors influencing arbovirus transmission: vector competence and the effects of virus infection on repellent response, oxidative stress, and glutathione-S-transferase activityChan, Kevin Ki Fai 31 January 2020 (has links)
Zika (ZIKV), La Crosse (LACV), and Cache Valley (CVV) viruses are mosquito-vectored diseases that cause significant morbidity and mortality in humans and animals. Transmission of these viruses are dependent on numerous factors including vector competence and the effects of mosquito-virus interactions. We conducted vector competence studies of local Aedes and Culex mosquitoes for ZIKV and CVV, and found that all Aedes mosquitoes were competent for CVV and only Aedes albopictus and Aedes japonicus were competent for ZIKV. Vector competence for CVV was dose-dependent, where mosquitoes orally infected with high titers developed higher transmission rates. We also found that vector competence for ZIKV was limited by midgut and salivary gland barriers. Second, we looked at the effects of LACV and ZIKV infection on repellent response in Aedes mosquitoes and found that infected mosquitoes were refractory to low concentrations of DEET, picaridin, and PMD. Increasing concentrations of the repellents to ≥10% was able to increase percent protection (%p) against infected and uninfected mosquitoes. Lastly, we determined the effects of ZIKV and LACV infection on oxidative stress and glutathione-S-transferase (GST) activity in Aedes albopictus. Virus infection had no effect on oxidative stress, but GST activity was significantly different for mosquitoes 3-days post-exposure. We found that oxidative stress levels and GST activity had an inverse relationship for infected and uninfected mosquitoes, where oxidative stress decreased and GST activity increased over the 10-day test period. This indicates that GSTs may aid in controlling byproducts of oxidative stress. The results from this entire study identified competent vectors for emerging arboviruses and demonstrated the behavioral and physiological effects of virus infection in the mosquito vector. / Doctor of Philosophy / Zika (ZIKV), La Crosse (LACV), and Cache Valley (CVV) viruses are transmitted by mosquitoes and can make humans and animals very sick. There are many biological factors that determine if a mosquito can transmit a virus and these viruses can change the biology of a mosquito. We conducted laboratory studies to see if Aedes and Culex mosquitoes can transmit ZIKV and CVV. We found that all Aedes mosquitoes were able to transmit CVV and only the Asian tiger mosquito and Asian rock pool mosquito were able to transmit ZIKV. Mosquitoes infected with high amounts of CVV developed higher transmission rates. We also found that transmission of ZIKV was limited by barriers in the mosquito midgut and salivary glands. Second, we looked at the effects of LACV and ZIKV infection on how Aedes mosquitoes respond to repellents and found that infected mosquitoes were less sensitive to low concentrations of DEET, picaridin, and PMD. Increasing concentrations of the repellents to 10% or higher was able to provide adequate protection against infected and uninfected mosquitoes. Lastly, we determined the effects of ZIKV and LACV infection on oxidative stress and glutathione-S-transferase (GST) activity in the Asian tiger mosquito. Virus infection did not change oxidative stress, but GST activity was higher in infected mosquitoes tested after 3 days after infection. We found that oxidative stress decreased and GST activity increased over the 10-day test period. This indicates that GSTs may help control damaging products from oxidative stress. The results from this entire study identified what mosquitoes were able to transmit emerging mosquito-borne viruses and demonstrated the biological effects of virus infection in the mosquitoes.
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La microarchitecture dans l'orfèvrerie religieuse florentine (1400-1570) : objectum, aediculum, imago / Microarchitecture in Florentine religious goldsmithery (1400-1570) : objectum, aediculum, imagoDelage, Alice 19 February 2018 (has links)
Depuis une vingtaine d’années, les historiens de l’art s’intéressent de près à la microarchitecture, c’est-à-dire la miniaturisation d’édifices dans les oeuvres d’art, en particulier dans l’orfèvrerie. Les études sur le sujet se concentrent toutefois essentiellement sur la période médiévale et s’attachent à définir dans quelle mesure ces oeuvres imitent des édifices existants. Elles sont rarement étendues à d’autres périodes. Or, la Renaissance florentine, marquée par une mutation profonde de l’art d’édifier et de concevoir l’architecture, constitue une fenêtre d’observation privilégiée, que nous mettons à profit pour explorer les liens que les édifices miniaturisés en orfèvrerie entretiennent avec leurs homologues monumentaux architecturés. Pour ce faire, nous identifions trois fonctions de la microarchitecture : celle d’objet ou de partie d’un objet (Objectum), celle d’assemblage d’éléments architecturaux (Ædiculum), celle d’image offerte au regard du spectateur (Imago). Dans Objectum, la microarchitecture est envisagée à travers la pièce d’orfèvrerie qu’elle contribue à orner, son contexte de fabrication et sa matérialité. Cet examen est aussi l’occasion de présenter les matériaux et les techniques utilisées en orfèvrerie. Ædiculum est consacré à l’étude des éléments architecturaux qui composent les petits édifices. Ces éléments mettent au jour des correspondances entre l’orfèvrerie et d’autres arts, tels que la sculpture ou la peinture. Dans Imago, nous montrons que les petites dimensions de la microarchitecture, qui la rendent propre à être embrassée du regard, en font une image qui engage un dialogue privilégié avec le spectateur grâce à un ensemble de dispositifs, qui vont de ses qualités esthétiques à sa capacité évocatrice en passant par les significations religieuses et politiques dont elle est chargée. Au total, cette étude montre que la microarchitecture ne se définit pas nécessairement dans son rapport avec la grande architecture mais consiste plutôt en un phénomène artistique indépendant et universel. / For the last twenty years art historians have developed an interest in microarchitecture: the miniaturization of architecture in works of art, especially in goldsmithery. Studies dedicated to the topic mostly focus on medieval period, trying to define which large-scale buildings these works might imitate. However, these studies are rarely extended to other periods of time. Renaissance Florence, characterized by a deep transformation of the art of architecture, is a significant period we chose in order to observe the connections between miniaturized and monumental buildings. This requires the identification of three aspects of microarchitecture: being an object or part of an object (Objectum), combining different architectural motives (Ædiculum) and presenting itself as an image to be seen by a viewer (Imago). With Objectum, we examine the microarchitecture in relation to the work it contributes to ornate as well as within its context of production. This inspection is also a relevant opportunity to present the materials and the techniques used by the goldsmiths. With Ædicula, we study the architectural motives that compose the miniaturized buildings. The motives show the similarities between goldsmithery and other arts like sculpture and painting. With Imago, we consider the dialog that microarchitecture establishes with the viewer thanks to several dispositives such as the æsthetic qualities of the pieces, their ability to evocated something familiar (a building) and, sometimes, their religious and political meanings. In total, this study argues that micorarchitecture does not necessarily define itself within its relationship to large-scale architecture but should rather be understood as an independent, universal artistic phenomenon.
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