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.

Aklilu Lemma Institute of Pathobiology Addis Ababa University Addis Ababa Ethiopia Ethiopia

Department of Biostatistics School of Public Health Yale University 60 College street New Haven CT 06520 USA USA

Department of Geography and Environmental Studies Haifa University Haifa Israel Israel

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

Department of Parasitology Faculty of Science Charles University Vinicna 7 128 44 Prague 2 Czech Republic Czech Republic

Dept of Microbiology Immunology and Parasitology Faculty of Medicine Addis Ababa University Addis Ababa Ethiopia Ethiopia

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