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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

The importance of climatic and ecological factors for vector-borne infections: Culex pipiens and West Nile virus

Marini, Giovanni January 2017 (has links)
About three quarters of human emerging infectious diseases are caused by zoonotic pathogens, and many of them are spread by vectors such as mosquitoes. Mathematical models nowadays represent very powerful tools to make investigations and predictions for biological dynamical systems, providing helpful insights that can be extremely valuable for several aims. In this thesis, we will focus on a particular mosquito-borne zoonosis, West Nile virus (WNV), a flavivirus of emerging public health relevance in Europe and North America, and its main European vector, Culex pipiens mosquitoes. As the transmission of mosquito-borne diseases is largely driven by the abundance of the vector, to design appropriate control strategies it is crucial to understand the population dynamics of existing vector populations and evaluate how it depends on biotic and environmental factors. This thesis presents some new mathematical models that provide insights on several aspects of mosquito population dynamics by using different statistical and computational approaches, including for instance Linear Models and Markov chain Monte Carlo technique. Specifically, they aim to study the effect of biotic and abiotic factors on Cx. pipiens dynamics by using adult mosquito trapping data, gathered over several years in Northern Italy, to feed theoretical models. Furthermore, the effects of host competition and vector feeding preferences on the dynamics of a vector-borne infection (such as WNV) are investigated through a more theoretical study.
12

West Nile virus in Italy: beyond the bird routes

Mencattelli, Giulia 09 June 2023 (has links)
Context: West Nile virus (WNV) is an arthropod-borne virus considered a One Health challenge because of its increasing impact on human and animal health. It is one the most widely distributed viruses of the encephalitic Flaviviruses. It may cause severe neurological symptoms in humans and animals and is recognized as a serious public health problem also because of its impact on blood transfusion and organ transplantation. First identified in Africa in 1937, it was later introduced and spread in Italy, where in many regions it is now endemic, due to the increasingly favorable climatic and environmental conditions. Aim: The main objectives of this study, based on an interdisciplinary One Health approach, were: (1) to characterize the geographical distribution within specific host and vector populations in Africa; (2) to describe its phylogeographical patterns between Africa and Europe; (3) to define the genetic structure and epidemiology of Italian WNV strains, giving an insight of the viral circulation dynamics in the Italian territory. Methodology: Ecological and epidemiological studies were combined with molecular and phylogenetic analyses, carrying out field sampling activities, cellular culture, viral infection, immunofluorescent assay, multiplexed RT-PCR, sequencing, data analysis, and novel technique design. These activities were carried out both in Italy and in Senegal. Results: Our study evidences: (i) the circulation of several WNV lineages [Lineage 1 (L1), 2 (L2), 7 (L7), and 8 (L8)] in the African Continent; (ii) the presence of diverse competent mosquito vectors in Africa, mainly belonging to the Culex genus; (iii) the lack of vector competence studies for several other mosquito species found naturally infected with WNV in Africa; (iv) the need of more vector competence studies on ticks; (v) the circulation of WNV among humans, animals and vectors in at least 28 African countries; (vi) the lack of knowledge on the epidemiological situation of WNV for 19 African countries, and (vii) the importance of carrying out specific serological surveys in order to avoid possible bias on WNV circulation in Africa (objective 1). Furthermore, a new set of WNV L1 and L2 genome-specific primers for tiled-amplicon sequencing have been designed and a consistent dataset of 64 WNV L2 and 31 WNV L1 Italian genomes and of 3 WNV L2 and 7 WNV L1 Senegalese genome sequences from samples collected in Italy and Senegal between 2006 and 2022 has been produced. Twenty more WNV L1 and L2 Senegalese sequences obtained from samples collected in Senegal between 1985 and 2018 have been shared by the Institut Pasteur Dakar of Senegal and added to the dataset. This allowed the conduction of phylogenetic and phylogeographic analyses, evidencing: (viii) the presence of a strong viral connection between Africa and Europe, with intercontinental circulation supported by birds crossing international boundaries while migrating through the African-Eurasian flyways; (ix) the WNV L1 Western-Mediterranean cluster probable spread from Senegal, where the virus was first reported in 1979, to Italy, where the lineage first appeared in Europe in 1998, and to France in 2000, and the presence of back re-introductory events from Italy, Spain, and France to North and West Africa from the 2010s; and (x) the first African introduction of WNV L2 in Europe in Hungary in 2004, possibly from South African countries (objective 2). Our study also gives an insight of the dynamics of the viral circulation in Italy, demonstrating: (xi) the endemic presence of WNV L1 and L2 in part of Italy supported by resident wild birds and vector competent mosquitoes mainly belonging to the Culex genus; (xii) the current existence of two diverse WNV L1 strains circulating in Italy, one in the North-East, and one circulating intra-regionally in the Campania region; (xiii) suggested characteristic silent periods observed for WNV L1 in the country, with unnoticed circulation lasting sometimes for more than 10 years; (xiv) the 2022 WNV L1 increasing incidence of neurological disease cases in humans; (xv) the presence of genetically stable WNV L2 strains in Italy with continuous circulation throughout the time; (xvi) the presence of overwintering mechanisms supported by bird-to bird, rodent-to bird, or mosquito-to bird transmission routes; (xvii) the existence of WNV L1 and L2 co-infections in birds and mosquitoes; (xviii) the existence of a continuous transmission of the two strains between Western Mediterranean countries, supported by short distance migratory birds; and (xix) the crucial importance of the surveillance system other than the strategic role of wildlife rescue centers in monitoring both the introduction and circulation of avian emerging zoonotic diseases in Italy (objective 3). Conclusion: Our work points out the existence of high genetic diversity of WNV strains in Africa, the spread of L1 and L2 strains from Africa to Europe, and the existence of continuous transmission episodes among several Western-Mediterranean countries, with few recently suspected back introductory events from Europe to Africa. The progressive increase of the WNV L2 circulation both temporally and spatially in the Mediterranean countries and the WNV L1 re-appearance in Europe, both associated with a significant impact on humans and animal health, other than the strong WNV incidence in Italy and its endemization in part of its territory, evidence a solid WNV epidemic risk for Italy and a persistent threat for WNV spread into new areas. To predict and control future epidemics, it is crucial to constantly monitor the circulation and evolution of WNV in Europe and Africa, and to implement coordinated surveillance plans in both Continents, even in areas which are not currently affected.
13

Studio della storia evoluzionistica e conservazione delle specie zootecniche attraverso analisi di genomica del paesaggio e modelli di nicchia ecologica / EXPLORING LIVESTOCK EVOLUTIONARY HISTORY, DIVERSITY, ADAPTATION AND CONSERVATION THROUGH LANDSCAPE GENOMICS AND ECOLOGICAL MODELLING

VAJANA, ELIA 31 May 2017 (has links)
Attività antropiche e pressioni di mercato stanno rapidamente riducendo la biodiversità. Per questa ragione, conservare il patrimonio ecosistemico, tassonomico e genetico risulta fondamentale al fine di garantire potenziale adattativo alle specie, e, in ultima analisi, un futuro sostenibile per il pianeta. Al fine di minimizzare la perdita di biodiversità, numerosi metodi sono stati proposti per priorizzare ecosistemi, specie e popolazioni. Il presente lavoro di tesi fornisce in primo luogo una revisione di tali approcci, proponendo un albero decisionale volto a favorirne un corretto utilizzo. Secondariamente, la variabilità genomica neutrale del bufalo d’acqua (Bubalus bubalis L.) è investigata per mezzo di un pannello di marcatori SNP a media densità, rivelando due centri di domesticazione (India Nord-occidentale, Cina-Indocina) e possibili rotte di migrazione per gli ecotipi ‘river’ e ‘swamp’. L’adattamento locale ad East Coast Fever, patologia endemica delle popolazioni bovine in Africa Sub-sahariana, è stato inoltre studiato in bovini autoctoni Ugandesi (Bos taurus L.) combinando tecniche di modellizzazione delle nicchie ecologiche e di genomica del paesaggio. L’approccio ha portato ad indentificare PRKG1 e SLA2 come possibili geni di adattamento. I risultati sono discussi alla luce delle possibili implicazioni nella conservazione del bufalo e nella gestione delle risorse genetiche animali Ugandesi. / Biodiversity is quickly disappearing due to human impact on the biosphere, and to market pressure. Consequently, the protection of both wild and domestic species needs to become a priority in order to preserve their evolutionary potential and, ultimately, guarantee a sustainable future for coming human generations. To date, tens of methods have been proposed to prioritize biodiversity for conservation purposes. Here, an ontology for priority setting in conservation biology is provided with the aim of supporting the selection of the most opportune methodologies given specific conservation goals. Further, two case studies are presented characterizing neutral and adaptive genomic diversity in water buffalo (Bubalus bubalis L.) and indigenous Ugandan cattle (Bos taurus L.), respectively. In particular, two independent domestication centres (North-western India and Indochina) and separate migration routes are suggested for the ‘river’ and ‘swamp’ water buffalo types. In the case of indigenous Ugandan cattle, the integration of species distribution modelling and landscape genomics techniques allowed the identification of PRKG1 and SLA2 as candidate genes for local adaptation to East Coast Fever, a vector-borne disease affecting bovine populations of Sub-Saharan Africa. Results are discussed for their implications in water buffalo conservation and Ugandan cattle adaptive management.

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