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Widely spaced tidal gravity records have been used to determine the spatial and temporal variation of the ocean tide beneath the Ross Ice Shelf. Cotidal-coamplitude maps have been drawn for the six greatest harmonic constituents of the tide. These are K₁, P₁, O₁, M₂, S₂, and N₂. The tide is principally diurnal, the diurnal amplitudes being roughly 3 times longer than the semidiurnals. The range of the tropic tide is about 1 m at the northern extremity of the ice shelf, and can be as great as 2 m in the southeastern part of the region. The diurnal constituents can each be viewed as a wave that propagates towards the southwest across the sea, having an amplitude that is closely related to the thickness of the water-layer beneath the ice. For each of the semidiurnal constituents there is an amphidromic region located within the Ross 5ea near 80° S latitude, 1900 W longitude, and having a clockwise sense of rotation. Theoretical calculations of the tidal current indicate that the semidiurnal and diurnal current constituents have roughly the same amplitude. The semidiurnal current is magnified by near resonance with the inertia current due to the high latitude of the sea. Because of the resonance, calculations of the semidiurnal components of the tidal current are sensitive to the treatment of the retarding effects of the ice shelf and sea floor. Waves having periods shorter than 20 min were observed in the ice shelf. These have been identified as flexural waves that are generated by the action of the ocean swell on the northern edge of the shelf. The observed speed of these waves was predicted within the uncertainty of the measurement by the classical flexural wave theory. / Ph. D.

[Truncated abstract] Ross River virus (RRV) causes the most common arboviral disease in Australia, with approximately 5000 new cases reported each year, making this virus a major public health concern. The aim of this thesis was to link results from virological, pathogenesis and epidemiological studies to further define RRV disease in the south-west (SW) of Western Australia (WA), a region of endemic and epizootic RRV activity. A crosssectional seroprevalence study was used to show that 7.8 percent of SW communities were seropositive to RRV, comparable to other regions of Australia with similar temperate climates to the SW . . . RRV-specific IgM antibodies were found to persist for at least two years following RRV infection. A murine model was used to conclusively show differences in pathogenesis between RRV genotypes, the SW and northern-eastern (NE) genotypes, which are known to circulate throughout Australia. The SW genotype, unique to the SW of WA induced only poor neutralising antibody production and nonneutralising antibodies after the acute phase of infection. In comparison, the NE genotype which currently predominates in mosquito populations in the SW of WA, induced the most efficient neutralising antibody response and consequently produced the mildest disease in the mouse. These data in the mouse suggest that the infecting genotype will mostly likely influence disease outcome in humans and could at least partially explain why more severe and persistent disease has been reported from the SW of WA. Collectively, results from this thesis provide an important benchmark against which future investigations into BFV and RRV diseases can be measured.

[Truncated abstract] A functional ecosystem is increasingly being recognised as a requirement for health and well being of resident human populations. Clearing of native vegetation for agriculture has left 1.047 million hectares of south-west Western Australia affected by a severe form of environmental degradation, dryland salinity, characterised by secondary soil salinisation and waterlogging. This area may expand by a further 1.7-3.4 million hectares if current trends continue. Ecosystems in saline affected regions display many of the classic characteristics of Ecosystem Distress Syndrome (EDS). One outcome of EDS that has not yet been investigated in relation to dryland salinity is adverse human health implications. This thesis focuses on one such potential adverse health outcome: increased incidence of Ross River virus (RRV), the most common mosquito-borne disease in Australia. Spatial analysis of RRV notifications did not reveal a significant association with dryland salinity. To overcome inherent limitations with notification data, serological RRV antibody prevalence was also investigated, and again no significant association with dryland salinity was detected. However, the spatial scale imposed limited the sensitivity of both studies. ... This thesis represents the first attempt to prospectively investigate the influence of secondary soil salinity on mosquito-borne disease by combining entomological, environmental and epidemiological data. The evidence collected indicates that RRV disease incidence is not currently a significant population health priority in areas affected by dryland salinity despite the dominant presence of Ae. camptorhynchus. Potential limiting factors include; local climatic impact on the seasonal mosquito population dynamics; vertebrate host distribution and feeding behaviour of Ae. camptorhynchus; and the scarce and uneven human population distribution across the region. However, the potential for increased disease risk in dryland salinity affected areas to become apparent in the future cannot be discounted, particularly in light of the increasing extent predicted to develop over coming decades before any benefits of amelioration strategies are observed. Finally, it is important to note that both dryland salinity and salinity induced by irrigation are important forms of environmental degradation in arid and semi-arid worldwide, with a total population of over 400 million people. Potential health risks will of course vary widely across different regions depending on a range of factors specific to the local region and the complex interactions between them. It is therefore not possible to make broad generalisations. The need is highlighted for similar research in other regions and it is contended that an ecosystem health framework provides the necessary basis for such investigations.

Thesis (Ph.D.)--University of Alberta, 2001. / Includes bibliographical references.

Les huiles essentielles de citronnelle (Cymbopogon citratus), de géranium (Pelargonium graveolens) et de vétiver (Vetiveria zizanioides) sont utilisées partout dans le monde pour leur activité répulsive contre les principaux vecteurs (moustiques, tiques) de maladies infectieuses chez l'Homme (paludisme, chikungunya, …). L'application cutanée de ces produits naturels pour éviter le contact avec un vecteur n'avait pas été encore envisagée comme moyen de limiter les premiers stades de l’infection par l'agent pathogène transmis par le vecteur. Pour vérifier cette hypothèse, les travaux ont été consacrés à la mise en place d'un cadre structuré pour la réévaluation chimique et biologique des trois huiles essentielles sur le modèle du virus du Ross River (alphavirus) de la même famille que le virus du Chikungunya. La caractérisation chimique des huiles essentielles avec une technique de haute résolution (GC×GC/TOF-MS) a permis d'établir leur profil chémotypique précis. L'utilisation de marqueurs spécifiques (clones moléculaires du virus) a permis d'établir l'inhibition de la réplication virale en fonction des conditions d'application des huiles essentielles de géranium et citronnelle. Ces résultats suggèrent l'intérêt d’une huile essentielle répulsive dans les premiers stades d'une infection par un vecteur. À ce titre, l'étude comparative établit la haute valeur ajoutée de l'huile essentielle de géranium et oriente la recherche de nouveaux anti-infectieux naturels vers des complexes riches en monoterpènes. / Essential oils of citronella (Cymbopogon citratus), geranium (Pelargonium graveolens) and vetiver (Vetiveria zizanioides) are used worldwide as topical repellent against the main vectors (mosquitoes, ticks) of human infectious diseases (Malaria, chikungunya, …). Skin treatment with these natural products, initially to avoid contact with the vector had not yet been considered as a way to disrupt the early stages of infection when the repelling action fails. To check this hypothesis, a structured framework has been performed for the chemical and biological re-evaluation of the three essential oils. The latter was tested against Ross River virus (alphavirus) that belongs to the same family of Chikungunya virus. Analysis of essential oils using a high-resolution technique (GC × GC / TOF-MS) resulted in a more accurate chemotypical profile of the local production. The use of specific markers (molecular clones of the virus, Saclay CEA) allowed to establish the inhibition of viral replication depending of the conditions of geranium and citronella essential oils application. These results suggest the great interest of an essential oil topical repellent in the early stages of a vector infection. The comparative study established the high value of geranium essential oil and gave future direction to the discovery of new anti-infectious solutions from monoterpenes-rich natural complexes.