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      A fine scale eco-epidemiological study on endemic visceral leishmaniasis in north ethiopian villages

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          Graphical abstract

          Hypothetical illustration of Anthroponotic Transmission Cycle of L. donovani in VL Endemic Villages in Northern Ethiopia. Transmission of L. donovani occurs anthroponotically in or close to households near to vertisols. Sand flies breeding in vertisols, are attracted into villages to feed blood on domestic animals, plant communities my serve as resting places for sand fly vectors.

          Highlights

          • We conducted fine-scale eco-epidemiological analyses of factors associated with visceral leishmaniasis transmission.
          • The population densities of Phlebotomus orientalis, the vector, were negatively correlated with distance from vertisols.
          • Sero-positivity to Ph. orientalis saliva, was found in people living close to vertisol areas.
          • Apparent clustering of infections indicates that transmission occurs around houses located close to vertisols.
          • Our data suggest that asymptomatic individuals serve as reservoir hosts for anthroponotic transmission inside villages.

          Abstract

          Visceral Leishmaniasis (VL) is a disseminated protozoan infection caused by Leishmania donovani that affects almost half a million people annually. In Northern Ethiopia, VL is common in migrant agricultural laborers returning from the lowland sesame fields of Metema and Humera. Recent VL foci have emerged in resident rural populations near the town. In the current study, we evaluate multilevel entomological, epidemiological and ecological factors associated with infection and disease through fine-scale eco-epidemiological analyses in three villages. Satellite images showed that villages constructed in or close to vertisols, were likely to become endemic for VL. Vertisols or black-cotton soil, are characterized by high contents of smectitic clay minerals, which swell when hydrated and shrink upon desiccation, causing extensive deep cracking during the dry season. The population densities of Phlebotomus orientalis, the vector, were negatively correlated with distance from vertisols and persons living close to vertisols were more likely to be bitten by sand flies, as evidenced by sero-positivity to Ph. orientalis saliva. Apparent (albeit non-significant) clustering of VL cases and abundant asymptomatic infections close to vertisols, suggest anthroponotic transmission around houses located close to vertisols. Comparable rates of male and female volunteers, mostly under 15 years of age, were infected with L. donovani but a significantly higher proportion of males succumbed to VL indicating a physiological gender-linked male susceptibility. Our data suggest that the abundant infected persons with high parasitemias who remain asymptomatic, may serve as reservoir hosts for anthroponotic transmission inside villages. Only limited insights on the transmission dynamics of L. donovani were gained by the study of environmental factors such as presence of animals, house structure and vegetation cover.

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          Most cited references 36

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          Visceral leishmaniasis: what are the needs for diagnosis, treatment and control?

          Visceral leishmaniasis (VL) is a systemic protozoan disease that is transmitted by phlebotomine sandflies. Poor and neglected populations in East Africa and the Indian sub-continent are particularly affected. Early and accurate diagnosis and treatment remain key components of VL control. In addition to improved diagnostic tests, accurate and simple tests are needed to identify treatment failures. Miltefosine, paromomycin and liposomal amphotericin B are gradually replacing pentavalent antimonials and conventional amphotericin B as the preferred treatments in some regions, but in other areas these drugs are still being evaluated in both mono- and combination therapies. New diagnostic tools and new treatment strategies will only have an impact if they are made widely available to patients.
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            Landscape epidemiology of vector-borne diseases.

            Landscape epidemiology describes how the temporal dynamics of host, vector, and pathogen populations interact spatially within a permissive environment to enable transmission. The spatially defined focus, or nidus, of transmission may be characterized by vegetation as well as by climate, latitude, elevation, and geology. The ecological complexity, dimensions, and temporal stability of the nidus are determined largely by pathogen natural history and vector bionomics. Host populations, transmission efficiency, and therefore pathogen amplification vary spatially, thereby creating a heterogeneous surface that may be defined by remote sensing and statistical tools. The current review describes the evolution of landscape epidemiology as a science and exemplifies selected aspects by contrasting the ecology of two different recent disease outbreaks in North America caused by West Nile virus, an explosive, highly virulent mosquito-borne virus producing ephemeral nidi, and Borrelia burgdorferi, a slowly amplifying chronic pathogen producing semipermanent nidi.
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              Landscape ecology and epidemiology of vector-borne diseases: tools for spatial analysis.

               U Kitron (1998)
              Geographic information systems (GIS), global positioning systems (GPS), remote sensing, and spatial statistics are tools to analyze and integrate the spatial component in epidemiology of vector-borne disease into research, surveillance, and control programs based on a landscape ecology approach. Landscape ecology, which deals with the mosaic structure of landscapes and ecosystems, considers the spatial heterogeneity of biotic and abiotic components as the underlying mechanism which determines the structure of ecosystems. The methodologies of GIS, GPS, satellite imagery, and spatial statistics, and the landscape ecology--epidemiology approach are described, and applications of these methodologies to vector-borne diseases are reviewed. Collaborative studies by the author and colleagues on malaria in Israel and tsetse flies in Kenya, and Lyme disease, LaCrosse encephalitis, and eastern equine encephalitis in the north-central United States are presented as examples for application of these tools to research and disease surveillance. Relevance of spatial tools and landscape ecology to emerging infectious diseases and to studies of global change effects on vector-borne diseases are discussed.
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                Author and article information

                Contributors
                Journal
                Acta Trop
                Acta Trop
                Acta Tropica
                Elsevier
                0001-706X
                1873-6254
                1 July 2018
                July 2018
                : 183
                : 64-77
                Affiliations
                [a ]Department of Microbiology and Molecular Genetics, The Institute of Medical Research, Israel-Canada [IMRIC], The Kuvin Centre for the Study of Infectious and Tropical Diseases, Faculty of Medicine, The Hebrew University of Jerusalem, Israel, Israel
                [b ]Department of Biostatistics, School of Public Health, Yale University,60 College street, New Haven, CT, 06520, USA, USA
                [c ]Aklilu Lemma Institute of Pathobiology, Addis Ababa University, Addis Ababa, Ethiopia, Ethiopia
                [d ]Dept. of Microbiology, Immunology and Parasitology, Faculty of Medicine, Addis Ababa University, Addis Ababa, Ethiopia, Ethiopia
                [e ]Department of Parasitology, Faculty of Science, Charles University, Vinicna 7, 128 44, Prague 2, Czech Republic, Czech Republic
                [f ]Department of Geography and Environmental Studies, Haifa University, Haifa, Israel, Israel
                Author notes
                [* ]Corresponding author. odkirstein@ 123456gmail.com
                [1]

                Deceased

                Article
                S0001-706X(18)30146-3
                10.1016/j.actatropica.2018.04.005
                5956276
                29621537
                © 2018 The Authors

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

                Categories
                Article

                Ecology

                visceral leishmaniasis, ethiopia, cohort study, ecoepidemiology, phlebotomine sand flies, vertisols

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