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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We are grateful to Mr. Haile Gebremariam, Mr. Wahalabi and Mr. Gebremaskel for his invaluable assistance, to Miss. Hadas Gebreyesus (nurse), for their help and coordination of the collection of the samples, to Mr. Kibrom Tafere and Mr. Shiwangzaw Sime (field drivers), and to all the study participants from Tahtay Adiyabo villages in Ethiopia. We are also grateful to Mr. Omer Bloch and Miss. Or'el Frenkel for their assistance with sand fly dissection and taxonomical classification and to Mrs. Tali Bdolah-Abram for the statistical advice and guidance. We also appreciate the help of Dr. Dan Malkinson for his support with GIS and spatial analysis . Lastly, we want to say thanks to Mrs. Ruthie Harari-Kerem for her helpful contribution with remote sensing analysis. This work was supported by the Bill and Melinda Gates Foundation Global Health Program (grant number OPPGH5336 ). The authors declare no conflicts of interest.
© 2018 The Authors
- Cohort study
- Phlebotomine sand flies
- Visceral leishmaniasis