Browsing by Subject "Agent-based modeling"
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Item Avian influenza in suphanburi province, Thailand: assessment of transmission dynamics and interventions in the local poultry sector.(2012-06) Beaudoin, Amanda LeighThis dissertation provides a review of avian influenza, with specific regard to highly pathogenic avian influenza (HPAI) H5N1, a description of the Thai poultry system and the country's experiences with influenza outbreaks, and discussions of both poultry and human exposure to and infection with HPAI H5N1. In addition, four research manuscripts provide insight into the relationship between influenza A, including HPAI H5N1, and poultry and human health in rural Suphanburi Province, Thailand. A major goal of this work was to learn more about the management of free-grazing duck (FGD) flocks in Thailand and their role in avian influenza virus maintenance and transmission. FGD have been associated with highly pathogenic avian influenza (HPAI) H5N1 outbreaks and may be a viral reservoir. In July-August 2010, the influenza exposure of Thai FGD and risk factors thereof were assessed. Sera from over 6000 FGDs were analyzed to detect antibodies to influenza A nucleoprotein (NP) and hemagglutinin H5 protein. Eighty-five percent were seropositive for influenza A. Of the NP-seropositive sera tested with H5 assays 39% were H5 ELISA-positive and 4% suspect. Twelve per cent of H5 ELISA-positive or suspect ducks had H5 titers ≥1:20. Risk factors for influenza A seropositivity include older age, poultry contact, flock visitors and older purchase age. Flocks had H5 virus exposure as recently as March 2010, but the last HPAI H5N1 outbreak in Thailand was in 2008, highlighting a need for FGD surveillance. This dissertation also includes an investigation of the seroprevalence of and risk factors for antibodies to HPAI H5N1 in poultry owners. Seroprevalence was 6.3%, and single persons and those working with farmed chickens were at increased risk of seropositivity. Poultry owners reported limited use of personal protective equipment during all activities and inconsistent hand washing practices after carrying poultry and gathering eggs. Lastly, this dissertation includes the description and results of an agent-based model (ABM) of the local Thai poultry sector which was built to simulate contacts among FGD flocks and persons that own poultry and conduct poultry-related activities. Using this model, opportunities for the transmission and control of HPAI H5N1 in this setting were identified.Item Intraurban migration in the Twin Cities of Minnesota.(2009-10) Sun, ShipengThis dissertation combines longstanding conceptual approaches--behavioral and economic--with aspects of complexity theory to analyze and model intraurban migration patterns in the Twin Cities Metropolitan Area (TCMA). It utilizes detailed parcel data records gathered for property tax purposes available for the seven-county TCMA. This parcel dataset has about six million parcel records covering six years from 2002 to 2007 describing attributes of land parcels, their owners, and the structures constructed on them. Using spatial data mining and modeling techniques, this research extracts spatially accurate information on individual household relocations, constructs vacancy chains, and examines their patterns and relation to residential structure and urban growth.Item Understanding transmission of Leptospira at the household level through an examination of human behaviors, environmental water contamination, and animal carriers(2016-10) Mason, MeghanObjective. Leptospirosis is a zoonotic disease that contributes to human morbidity and mortality worldwide, and is the result of contact between mucous membranes or broken skin and the urine of infected animals either directly, or through contaminated soil or water. Rodents, livestock, and dogs are all able to shed the Leptospira bacteria in their urine. This research seeks to contribute to the understanding of transmission dynamics of the pathogen through an examination of human behaviors, pathogen diversity, and interactions between animal hosts and the environment. Methods. The data for the studies presented in this thesis come primarily from the Eco-epidemiology of Leptospirosis study conducted in the Los Rios Region, Chile from 2010-2012. The study collected survey data from 422 households in twelve different communities representing rural farm areas (4 communities), rural villages (4 communities), and urban slums (4 communities). At each household, survey data, environmental water samples, and blood samples from humans and animals were obtained. Rodents were also trapped and euthanized. Polymerase Chain Reaction (PCR) methods were used to detect Leptospira in rodents and water samples, while Microscopic Agglutination Testing (MAT) identified humans and animals with evidence of prior leptospirosis infection. The secY region of PCR-positive water samples was amplified and sequenced for phylogenetic analysis. Additional observational data was collected in 2013 from dogs in urban slums and was used to create an agent-based model for leptospirosis transmission in NetLogo version 5.0.3. Results. There were no discernable patterns of Leptospira diversity across the three community types studied (rural farm areas, rural villages, and urban slums), but the diversity of the pathogen did vary across the twelve individual communities. L. interrogans, L. kirschneri, and L. weilli were found in all community types (rural farms, rural villages, and urban slums), in descending order of frequency. There was no evidence that community-level prevalence of Leptospira in dogs, rodents, or livestock influenced diversity of the pathogen in the environment. According to agent-based modeling, both rodents and dogs contribute to environmental contamination and subsequent human infection in urban slum areas, but dog-based interventions (culling of stray dogs, and vaccination and restricting movement of owned dogs) are not expected to reduce human incidence of the disease. Addressing indirect transmission of Leptospira from the environment to humans was identified through the agent-based model as a better approach to reducing incidence. Most households in the study (95%) reported participating in some form of rodent control, but practices such as wearing boots or gloves when working with livestock or in the garden were less common. The proportion of households that participated in protective practices against zoonotic infection was heavily dependent on the community in which the households existed. Conclusions. The transmission and diversity of leptospirosis in endemic areas is driven by community-level factors. Efforts to reduce transmission through human engagement in protective practices should address the needs and norms of the individual communities. These studies have provided the framework for systematic surveillance and modeling strategies that can help to inform communities about potential contaminated environments, identify changes in the ecology of the bacteria that may signal an uptick in human infection, and suggest targeted interventions. As future research improves diagnostic tools, understanding of the survival of the pathogen in the environment, and shedding patterns by animal hosts, these proposed methods can be refined to better serve the needs of communities where this neglected tropical disease is endemic.