Objective. 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.
University of Minnesota Ph.D. dissertation. October 2016. Major: Epidemiology. Advisors: Claudia Munoz-Zanzi, James Pankow. 1 computer file (PDF); viii, 186 pages.
Understanding transmission of Leptospira at the household level through an examination of human behaviors, environmental water contamination, and animal carriers.
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